"""A collection of GDAL dataset and raster utilities."""

import threading
import Queue
import logging
import os
import tempfile
import shutil
import atexit
import functools
import csv
import math
import errno
import collections
import exceptions
import heapq
import time
from types import StringType

from osgeo import gdal
from osgeo import osr
from osgeo import ogr
import numpy
import numpy.ma
import scipy.interpolate
import scipy.sparse
import scipy.signal
import scipy.ndimage
import scipy.signal.signaltools
import shapely.wkt
import shapely.ops
from shapely import speedups
import shapely.prepared

import geoprocessing_core
import fileio

AggregatedValues = collections.namedtuple(
    'AggregatedValues',
    'total pixel_mean hectare_mean n_pixels pixel_min pixel_max')

LOGGER = logging.getLogger('pygeoprocessing.geoprocessing')
_LOGGING_PERIOD = 5.0  # min 5.0 seconds per update log message for the module


class SpatialExtentOverlapException(Exception):
    """An exeception class for cases when datasets or datasources don't overlap
        in space.

    Used to raise an exception if rasters, shapefiles, or both don't overlap
        in regions that should.
    """
    pass


def _gdal_to_numpy_type(band):
    """Calculate the equivalent numpy datatype from a GDAL raster band type.

    Args:
        band (gdal.Band): GDAL band

    Returns:
        numpy_datatype (numpy.dtype): equivalent of band.DataType
    """

    gdal_type_to_numpy_lookup = {
        gdal.GDT_Int16: numpy.int16,
        gdal.GDT_Int32: numpy.int32,
        gdal.GDT_UInt16: numpy.uint16,
        gdal.GDT_UInt32: numpy.uint32,
        gdal.GDT_Float32: numpy.float32,
        gdal.GDT_Float64: numpy.float64
    }

    if band.DataType in gdal_type_to_numpy_lookup:
        return gdal_type_to_numpy_lookup[band.DataType]

    # only class not in the lookup is a Byte but double check.
    if band.DataType != gdal.GDT_Byte:
        raise ValueError("Unknown DataType: %s" % str(band.DataType))

    metadata = band.GetMetadata('IMAGE_STRUCTURE')
    if 'PIXELTYPE' in metadata and metadata['PIXELTYPE'] == 'SIGNEDBYTE':
        return numpy.int8
    return numpy.uint8



def get_nodata_from_uri(dataset_uri):
    """Return nodata value from first band in gdal dataset cast as numpy datatype.

    Args:
        dataset_uri (string): a uri to a gdal dataset

    Returns:
        nodata: nodata value for dataset band 1
    """
    dataset = gdal.Open(dataset_uri)
    band = dataset.GetRasterBand(1)
    nodata = band.GetNoDataValue()
    if nodata is not None:
        nodata = _gdal_to_numpy_type(band)(nodata)
    else:
        LOGGER.warn(
            "Warning the nodata value in %s is not set", dataset_uri)

    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None
    return nodata


def get_datatype_from_uri(dataset_uri):
    """Return datatype for first band in gdal dataset.

    Args:
        dataset_uri (string): a uri to a gdal dataset

    Returns:
        datatype: datatype for dataset band 1"""
    dataset = gdal.Open(dataset_uri)
    band = dataset.GetRasterBand(1)
    datatype = band.DataType

    # Close and clean up dataset
    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return datatype


def get_row_col_from_uri(dataset_uri):
    """Return number of rows and columns of given dataset uri as tuple.

    Args:
        dataset_uri (string): a uri to a gdal dataset

    Returns:
        rows_cols (tuple): 2-tuple (n_row, n_col) from dataset_uri
    """
    dataset = gdal.Open(dataset_uri)
    n_rows = dataset.RasterYSize
    n_cols = dataset.RasterXSize

    # Close and clean up dataset
    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return (n_rows, n_cols)


def calculate_raster_stats_uri(dataset_uri):
    """Calculate min, max, stdev, and mean for all bands in dataset.

    Args:
        dataset_uri (string): a uri to a GDAL raster dataset that will be
            modified by having its band statistics set

    Returns:
        None
    """

    dataset = gdal.Open(dataset_uri, gdal.GA_Update)

    for band_number in range(dataset.RasterCount):
        band = dataset.GetRasterBand(band_number + 1)
        band.ComputeStatistics(False)

    # Close and clean up dataset
    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None


def get_statistics_from_uri(dataset_uri):
    """Get the min, max, mean, stdev from first band in a GDAL Dataset.

    Args:
        dataset_uri (string): a uri to a gdal dataset

    Returns:
        statistics (tuple): min, max, mean, stddev

    """

    dataset = gdal.Open(dataset_uri)
    band = dataset.GetRasterBand(1)
    statistics = band.GetStatistics(0, 1)

    # Close and clean up dataset
    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return statistics


def get_cell_size_from_uri(dataset_uri):
    """Get the cell size of a dataset in units of meters.

    Raises an exception if the raster is not square since this'll break most of
    the pygeoprocessing algorithms.

    Args:
        dataset_uri (string): uri to a gdal dataset

    Returns:
        size_meters: cell size of the dataset in meters
    """

    srs = osr.SpatialReference()
    dataset = gdal.Open(dataset_uri)
    if dataset is None:
        raise IOError(
            'File not found or not valid dataset type at: %s' % dataset_uri)
    srs.SetProjection(dataset.GetProjection())
    linear_units = srs.GetLinearUnits()
    geotransform = dataset.GetGeoTransform()
    # take absolute value since sometimes negative widths/heights
    try:
        numpy.testing.assert_approx_equal(
            abs(geotransform[1]), abs(geotransform[5]))
        size_meters = abs(geotransform[1]) * linear_units
    except AssertionError as e:
        LOGGER.warn(e)
        size_meters = (
            abs(geotransform[1]) + abs(geotransform[5])) / 2.0 * linear_units

    # Close and clean up dataset
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return size_meters


def pixel_size_based_on_coordinate_transform_uri(dataset_uri, *args, **kwargs):
    """Get width and height of cell in meters.

    A wrapper for pixel_size_based_on_coordinate_transform that takes a dataset
    uri as an input and opens it before sending it along.

    Args:
        dataset_uri (string): a URI to a gdal dataset

        All other parameters pass along

    Returns:
        result (tuple): (pixel_width_meters, pixel_height_meters)
    """
    dataset = gdal.Open(dataset_uri)
    result = pixel_size_based_on_coordinate_transform(dataset, *args, **kwargs)

    # Close and clean up dataset
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return result


def pixel_size_based_on_coordinate_transform(dataset, coord_trans, point):
    """Get width and height of cell in meters.

    Calculates the pixel width and height in meters given a coordinate
    transform and reference point on the dataset that's close to the
    transform's projected coordinate sytem.  This is only necessary
    if dataset is not already in a meter coordinate system, for example
    dataset may be in lat/long (WGS84).

    Args:
        dataset (gdal.Dataset): a projected GDAL dataset in the form of
            lat/long decimal degrees
        coord_trans (osr.CoordinateTransformation): an OSR coordinate
            transformation from dataset coordinate system to meters
        point (tuple): a reference point close to the coordinate transform
            coordinate system.  must be in the same coordinate system as
            dataset.

    Returns:
        pixel_diff (tuple): a 2-tuple containing (pixel width in meters, pixel
            height in meters)
    """
    # Get the first points (x, y) from geoTransform
    geo_tran = dataset.GetGeoTransform()
    pixel_size_x = geo_tran[1]
    pixel_size_y = geo_tran[5]
    top_left_x = point[0]
    top_left_y = point[1]
    # Create the second point by adding the pixel width/height
    new_x = top_left_x + pixel_size_x
    new_y = top_left_y + pixel_size_y
    # Transform two points into meters
    point_1 = coord_trans.TransformPoint(top_left_x, top_left_y)
    point_2 = coord_trans.TransformPoint(new_x, new_y)
    # Calculate the x/y difference between two points
    # taking the absolue value because the direction doesn't matter for pixel
    # size in the case of most coordinate systems where y increases up and x
    # increases to the right (right handed coordinate system).
    pixel_diff_x = abs(point_2[0] - point_1[0])
    pixel_diff_y = abs(point_2[1] - point_1[1])
    return (pixel_diff_x, pixel_diff_y)


def new_raster_from_base_uri(
        base_uri, output_uri, gdal_format, nodata, datatype, fill_value=None,
        n_rows=None, n_cols=None, dataset_options=None):
    """Create a new, empty GDAL raster dataset with the spatial references,
    geotranforms of the base GDAL raster dataset.

    A wrapper for the function new_raster_from_base that opens up
    the base_uri before passing it to new_raster_from_base.

    Args:
        base_uri (string): a URI to a GDAL dataset on disk.
        output_uri (string): a string URI to the new output raster dataset.
        gdal_format (string): a string representing the GDAL file format of the
            output raster.  See http://gdal.org/formats_list.html for a list
            of available formats.  This parameter expects the format code, such
            as 'GTiff' or 'MEM'
        nodata: a value that will be set as the nodata value for the
            output raster.  Should be the same type as 'datatype'
        datatype: the pixel datatype of the output raster, for example
            gdal.GDT_Float32.  See the following header file for supported
            pixel types:
            http://www.gdal.org/gdal_8h.html#22e22ce0a55036a96f652765793fb7a4

    Keyword Args:
        fill_value: the value to fill in the raster on creation
        n_rows: if set makes the resulting raster have n_rows in it
            if not, the number of rows of the outgoing dataset are equal to
            the base.
        n_cols: similar to n_rows, but for the columns.
        dataset_options: a list of dataset options that gets
            passed to the gdal creation driver, overrides defaults

    Returns:
        nothing
    """
    geoprocessing_core.new_raster_from_base_uri(
        base_uri, output_uri, gdal_format, nodata, datatype,
        fill_value=fill_value, n_rows=n_rows, n_cols=n_rows,
        dataset_options=dataset_options)


def new_raster_from_base(
        base, output_uri, gdal_format, nodata, datatype, fill_value=None,
        n_rows=None, n_cols=None, dataset_options=None):
    """Create a new, empty GDAL raster dataset with the spatial references,
    geotranforms of the base GDAL raster dataset.

    Args:
        base: a the GDAL raster dataset to base output size, and transforms
            on
        output_uri (string): a string URI to the new output raster dataset.
        gdal_format (string): a string representing the GDAL file format of the
            output raster.  See http://gdal.org/formats_list.html for a list
            of available formats.  This parameter expects the format code, such
            as 'GTiff' or 'MEM'
        nodata: a value that will be set as the nodata value for the
            output raster.  Should be the same type as 'datatype'
        datatype: the pixel datatype of the output raster, for example
            gdal.GDT_Float32.  See the following header file for supported
            pixel types:
            http://www.gdal.org/gdal_8h.html#22e22ce0a55036a96f652765793fb7a4

    Keyword Args:
        fill_value: the value to fill in the raster on creation
        n_rows: if set makes the resulting raster have n_rows in it
            if not, the number of rows of the outgoing dataset are equal to
            the base.
        n_cols: similar to n_rows, but for the columns.
        dataset_options: a list of dataset options that gets
            passed to the gdal creation driver, overrides defaults

    Returns:
        dataset: a new GDAL raster dataset.
    """
    return geoprocessing_core.new_raster_from_base(
        base, output_uri, gdal_format, nodata, datatype, fill_value,
        n_rows, n_cols, dataset_options)


def new_raster(
        cols, rows, projection, geotransform, format, nodata, datatype,
        bands, outputURI):
    """Create a new raster with the given properties.

    Args:
        cols (int): number of pixel columns
        rows (int): number of pixel rows
        projection: the datum
        geotransform: the coordinate system
        format (string): a string representing the GDAL file format of the
            output raster.  See http://gdal.org/formats_list.html for a list
            of available formats.  This parameter expects the format code, such
            as 'GTiff' or 'MEM'
        nodata: a value that will be set as the nodata value for the
            output raster.  Should be the same type as 'datatype'
        datatype: the pixel datatype of the output raster, for example
            gdal.GDT_Float32.  See the following header file for supported
            pixel types:
            http://www.gdal.org/gdal_8h.html#22e22ce0a55036a96f652765793fb7a4
        bands (int): the number of bands in the raster
        outputURI (string): the file location for the outputed raster.  If
            format is 'MEM' this can be an empty string

    Returns:
        dataset: a new GDAL raster with the parameters as described above
    """
    driver = gdal.GetDriverByName(format)
    new_raster = driver.Create(
        outputURI.encode('utf-8'), cols, rows, bands, datatype,
        options=['BIGTIFF=IF_SAFER'])
    new_raster.SetProjection(projection)
    new_raster.SetGeoTransform(geotransform)
    for i in range(bands):
        new_raster.GetRasterBand(i + 1).SetNoDataValue(nodata)
        new_raster.GetRasterBand(i + 1).Fill(nodata)

    return new_raster


def calculate_intersection_rectangle(dataset_list, aoi=None):
    """Return bounding box of the intersection of all rasters in the list.

    Args:
        dataset_list (list): a list of GDAL datasets in the same projection and
            coordinate system

    Keyword Args:
        aoi: an OGR polygon datasource which may optionally also restrict
            the extents of the intersection rectangle based on its own
            extents.

    Returns:
        bounding_box (list): a 4 element list that bounds the intersection of
            all the rasters in dataset_list.  [left, top, right, bottom]

    Raises:
        SpatialExtentOverlapException: in cases where the dataset list and aoi
            don't overlap.
    """

    def valid_bounding_box(bb):
        """Check to make sure bounding box doesn't collapse on itself.

        Args:
            bb (list): a bounding box of the form [left, top, right, bottom]

        Returns:
            is_valid (boolean): True if bb is valid, false otherwise
        """

        return bb[0] <= bb[2] and bb[3] <= bb[1]

    # Define the initial bounding box
    gt = dataset_list[0].GetGeoTransform()
    # order is left, top, right, bottom of rasterbounds
    bounding_box = [
        gt[0], gt[3], gt[0] + gt[1] * dataset_list[0].RasterXSize,
        gt[3] + gt[5] * dataset_list[0].RasterYSize]

    dataset_files = []
    for dataset in dataset_list:
        dataset_files.append(dataset.GetDescription())
        # intersect the current bounding box with the one just read
        gt = dataset.GetGeoTransform()
        rec = [
            gt[0], gt[3], gt[0] + gt[1] * dataset.RasterXSize,
            gt[3] + gt[5] * dataset.RasterYSize]
        # This intersects rec with the current bounding box
        bounding_box = [
            max(rec[0], bounding_box[0]),
            min(rec[1], bounding_box[1]),
            min(rec[2], bounding_box[2]),
            max(rec[3], bounding_box[3])]

        # Left can't be greater than right or bottom greater than top
        if not valid_bounding_box(bounding_box):
            raise SpatialExtentOverlapException(
                "These rasters %s don't overlap with this one %s" %
                (unicode(dataset_files[0:-1]), dataset_files[-1]))

    if aoi != None:
        aoi_layer = aoi.GetLayer(0)
        aoi_extent = aoi_layer.GetExtent()
        bounding_box = [
            max(aoi_extent[0], bounding_box[0]),
            min(aoi_extent[3], bounding_box[1]),
            min(aoi_extent[1], bounding_box[2]),
            max(aoi_extent[2], bounding_box[3])]
        if not valid_bounding_box(bounding_box):
            raise SpatialExtentOverlapException(
                "The aoi layer %s doesn't overlap with %s" %
                (aoi, unicode(dataset_files)))

    return bounding_box


def create_raster_from_vector_extents_uri(
        shapefile_uri, pixel_size, gdal_format, nodata_out_value, output_uri):
    """Create a blank raster based on a vector file extent.

    A wrapper for create_raster_from_vector_extents

    Args:
        shapefile_uri (string): uri to an OGR datasource to use as the extents
            of the raster
        pixel_size: size of output pixels in the projected units of
            shapefile_uri
        gdal_format: the raster pixel format, something like
            gdal.GDT_Float32
        nodata_out_value: the output nodata value
        output_uri (string): the URI to write the gdal dataset

    Returns:
        dataset (gdal.Dataset): gdal dataset
    """
    datasource = ogr.Open(shapefile_uri)
    create_raster_from_vector_extents(
        pixel_size, pixel_size, gdal_format, nodata_out_value, output_uri,
        datasource)


def create_raster_from_vector_extents(
        xRes, yRes, format, nodata, rasterFile, shp):
    """Create a blank raster based on a vector file extent.

    This code is adapted from http://trac.osgeo.org/gdal/wiki/FAQRaster#HowcanIcreateablankrasterbasedonavectorfilesextentsforusewithgdal_rasterizeGDAL1.8.0

    Args:
        xRes: the x size of a pixel in the output dataset must be a
            positive value
        yRes: the y size of a pixel in the output dataset must be a
            positive value
        format: gdal GDT pixel type
        nodata: the output nodata value
        rasterFile (string): URI to file location for raster
        shp: vector shapefile to base extent of output raster on

    Returns:
        raster: blank raster whose bounds fit within `shp`s bounding box
            and features are equivalent to the passed in data
    """

    # Determine the width and height of the tiff in pixels based on the
    # maximum size of the combined envelope of all the features
    shp_extent = None
    for layer_index in range(shp.GetLayerCount()):
        shp_layer = shp.GetLayer(layer_index)
        for feature_index in range(shp_layer.GetFeatureCount()):
            try:
                feature = shp_layer.GetFeature(feature_index)
                geometry = feature.GetGeometryRef()

                # feature_extent = [xmin, xmax, ymin, ymax]
                feature_extent = geometry.GetEnvelope()
                # This is an array based way of mapping the right function
                # to the right index.
                functions = [min, max, min, max]
                for i in range(len(functions)):
                    try:
                        shp_extent[i] = functions[i](
                            shp_extent[i], feature_extent[i])
                    except TypeError:
                        # need to cast to list because returned as a tuple
                        # and we can't assign to a tuple's index, also need to
                        # define this as the initial state
                        shp_extent = list(feature_extent)
            except AttributeError as e:
                # For some valid OGR objects the geometry can be undefined
                # since it's valid to have a NULL entry in the attribute table
                # this is expressed as a None value in the geometry reference
                # this feature won't contribute
                LOGGER.warn(e)

    tiff_width = int(numpy.ceil(abs(shp_extent[1] - shp_extent[0]) / xRes))
    tiff_height = int(numpy.ceil(abs(shp_extent[3] - shp_extent[2]) / yRes))

    if rasterFile is not None:
        driver = gdal.GetDriverByName('GTiff')
    else:
        rasterFile = ''
        driver = gdal.GetDriverByName('MEM')
    # 1 means only create 1 band
    raster = driver.Create(
        rasterFile, tiff_width, tiff_height, 1, format,
        options=['BIGTIFF=IF_SAFER'])
    raster.GetRasterBand(1).SetNoDataValue(nodata)

    # Set the transform based on the upper left corner and given pixel
    # dimensions
    raster_transform = [shp_extent[0], xRes, 0.0, shp_extent[3], 0.0, -yRes]
    raster.SetGeoTransform(raster_transform)

    # Use the same projection on the raster as the shapefile
    srs = osr.SpatialReference()
    srs.ImportFromWkt(shp.GetLayer(0).GetSpatialRef().__str__())
    raster.SetProjection(srs.ExportToWkt())

    # Initialize everything to nodata
    raster.GetRasterBand(1).Fill(nodata)
    raster.GetRasterBand(1).FlushCache()

    return raster


def vectorize_points_uri(
        shapefile_uri, field, output_uri, interpolation='nearest'):
    """Interpolate values in shapefile onto given raster.

    A wrapper function for pygeoprocessing.vectorize_points, that allows for
    uri passing.

    Args:
        shapefile_uri (string): a uri path to an ogr shapefile
        field (string): a string for the field name
        output_uri (string): a uri path for the output raster
        interpolation (string): interpolation method to use on points, default
            is 'nearest'

    Returns:
        None
    """

    datasource = ogr.Open(shapefile_uri)
    output_raster = gdal.Open(output_uri, 1)
    vectorize_points(
        datasource, field, output_raster, interpolation=interpolation)


def vectorize_points(
        shapefile, datasource_field, dataset, randomize_points=False,
        mask_convex_hull=False, interpolation='nearest'):
    """Interpolate values in shapefile onto given raster.

    Takes a shapefile of points and a field defined in that shapefile
    and interpolate the values in the points onto the given raster

    Args:
        shapefile: ogr datasource of points
        datasource_field: a field in shapefile
        dataset: a gdal dataset must be in the same projection as shapefile

    Keyword Args:
        randomize_points (boolean): (description)
        mask_convex_hull (boolean): (description)
        interpolation (string): the interpolation method to use for
            scipy.interpolate.griddata(). Default is 'nearest'

    Returns:
       None
    """

    # Define the initial bounding box
    gt = dataset.GetGeoTransform()
    # order is left, top, right, bottom of rasterbounds
    bounding_box = [gt[0], gt[3], gt[0] + gt[1] * dataset.RasterXSize,
                    gt[3] + gt[5] * dataset.RasterYSize]

    def in_bounds(point):
        return point[0] <= bounding_box[2] and point[0] >= bounding_box[0] \
            and point[1] <= bounding_box[1] and point[1] >= bounding_box[3]

    layer = shapefile.GetLayer(0)
    point_list = []
    value_list = []

    # Calculate a small amount to perturb points by so that we don't
    # get a linear Delauney triangle, the 1e-6 is larger than eps for
    # floating point, but large enough not to cause errors in interpolation.
    delta_difference = 1e-6 * min(abs(gt[1]), abs(gt[5]))
    if randomize_points:
        random_array = numpy.random.randn(layer.GetFeatureCount(), 2)
        random_offsets = random_array*delta_difference
    else:
        random_offsets = numpy.zeros((layer.GetFeatureCount(), 2))

    for feature_id in range(layer.GetFeatureCount()):
        feature = layer.GetFeature(feature_id)
        geometry = feature.GetGeometryRef()
        # Here the point geometry is in the form x, y (col, row)
        point = geometry.GetPoint()
        if in_bounds(point):
            value = feature.GetField(datasource_field)
            # Add in the numpy notation which is row, col
            point_list.append([point[1]+random_offsets[feature_id, 1],
                               point[0]+random_offsets[feature_id, 0]])
            value_list.append(value)

    point_array = numpy.array(point_list)
    value_array = numpy.array(value_list)

    band = dataset.GetRasterBand(1)

    # Create grid points for interpolation outputs later
    # top-bottom:y_stepsize, left-right:x_stepsize

    # Make as an integer grid then divide subtract by bounding box parts
    # so we don't get a roundoff error and get off by one pixel one way or
    # the other
    grid_y, grid_x = numpy.mgrid[0:band.YSize, 0:band.XSize]
    grid_y = grid_y * gt[5] + bounding_box[1]
    grid_x = grid_x * gt[1] + bounding_box[0]
    nodata = band.GetNoDataValue()

    raster_out_array = scipy.interpolate.griddata(
        point_array, value_array, (grid_y, grid_x), interpolation, nodata)
    band.WriteArray(raster_out_array, 0, 0)

    # Make sure the dataset is closed and cleaned up
    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None


def aggregate_raster_values_uri(
        raster_uri, shapefile_uri, shapefile_field=None, ignore_nodata=True,
        all_touched=False, polygons_might_overlap=True):
    """Collect stats on pixel values which lie within shapefile polygons.

    Args:
        raster_uri (string): a uri to a raster.  In order for hectare
            mean values to be accurate, this raster must be projected in
            meter units.
        shapefile_uri (string): a uri to a OGR datasource that should overlap
            raster; raises an exception if not.

    Keyword Args:
        shapefile_field (string): a string indicating which key in shapefile to
            associate the output dictionary values with whose values are
            associated with ints; if None dictionary returns a value over
            the entire shapefile region that intersects the raster.
        ignore_nodata: if operation == 'mean' then it does not
            account for nodata pixels when determining the pixel_mean,
            otherwise all pixels in the AOI are used for calculation of the
            mean.  This does not affect hectare_mean which is calculated from
            the geometrical area of the feature.
        all_touched (boolean): if true will account for any pixel whose
            geometry passes through the pixel, not just the center point
        polygons_might_overlap (boolean): if True the function calculates
            aggregation coverage close to optimally by rasterizing sets of
            polygons that don't overlap.  However, this step can be
            computationally expensive for cases where there are many polygons.
            Setting this flag to False directs the function rasterize in one
            step.

    Returns:
        result_tuple (tuple): named tuple of the form
           ('aggregate_values', 'total pixel_mean hectare_mean n_pixels
            pixel_min pixel_max')
           Each of [sum pixel_mean hectare_mean] contains a dictionary that
           maps shapefile_field value to the total, pixel mean, hecatare mean,
           pixel max, and pixel min of the values under that feature.
           'n_pixels' contains the total number of valid pixels used in that
           calculation.  hectare_mean is None if raster_uri is unprojected.

    Raises:
        AttributeError
        TypeError
        OSError
    """
    raster_nodata = get_nodata_from_uri(raster_uri)
    out_pixel_size = get_cell_size_from_uri(raster_uri)
    clipped_raster_uri = temporary_filename(suffix='.tif')
    vectorize_datasets(
        [raster_uri], lambda x: x, clipped_raster_uri, gdal.GDT_Float64,
        raster_nodata, out_pixel_size, "union",
        dataset_to_align_index=0, aoi_uri=shapefile_uri,
        assert_datasets_projected=False, vectorize_op=False)
    clipped_raster = gdal.Open(clipped_raster_uri)

    # This should be a value that's not in shapefile[shapefile_field]
    mask_nodata = -1
    mask_uri = temporary_filename(suffix='.tif')
    new_raster_from_base_uri(
        clipped_raster_uri, mask_uri, 'GTiff', mask_nodata,
        gdal.GDT_Int32, fill_value=mask_nodata)

    mask_dataset = gdal.Open(mask_uri, gdal.GA_Update)
    shapefile = ogr.Open(shapefile_uri)
    shapefile_layer = shapefile.GetLayer()
    rasterize_layer_args = {
        'options': [],
    }

    if all_touched:
        rasterize_layer_args['options'].append('ALL_TOUCHED=TRUE')

    if shapefile_field is not None:
        # Make sure that the layer name refers to an integer
        layer_d = shapefile_layer.GetLayerDefn()
        field_index = layer_d.GetFieldIndex(shapefile_field)
        if field_index == -1:  # -1 returned when field does not exist.
            # Raise exception if user provided a field that's not in vector
            raise AttributeError(
                'Vector %s must have a field named %s' %
                (shapefile_uri, shapefile_field))

        field_def = layer_d.GetFieldDefn(field_index)
        if field_def.GetTypeName() != 'Integer':
            raise TypeError(
                'Can only aggregate by integer based fields, requested '
                'field is of type  %s' % field_def.GetTypeName())
        # Adding the rasterize by attribute option
        rasterize_layer_args['options'].append(
            'ATTRIBUTE=%s' % shapefile_field)
    else:
        # 9999 is a classic unknown value
        global_id_value = 9999
        rasterize_layer_args['burn_values'] = [global_id_value]

    # loop over the subset of feature layers and rasterize/aggregate each one
    aggregate_dict_values = {}
    aggregate_dict_counts = {}
    result_tuple = AggregatedValues(
        total={},
        pixel_mean={},
        hectare_mean={},
        n_pixels={},
        pixel_min={},
        pixel_max={})

    # make a shapefile that non-overlapping layers can be added to
    driver = ogr.GetDriverByName('ESRI Shapefile')
    layer_dir = temporary_folder()
    subset_layer_datasouce = driver.CreateDataSource(
        os.path.join(layer_dir, 'subset_layer.shp'))
    spat_ref = get_spatial_ref_uri(shapefile_uri)
    subset_layer = subset_layer_datasouce.CreateLayer(
        'subset_layer', spat_ref, ogr.wkbPolygon)
    defn = shapefile_layer.GetLayerDefn()

    # For every field, create a duplicate field and add it to the new
    # subset_layer layer
    defn.GetFieldCount()
    for fld_index in range(defn.GetFieldCount()):
        original_field = defn.GetFieldDefn(fld_index)
        output_field = ogr.FieldDefn(
            original_field.GetName(), original_field.GetType())
        subset_layer.CreateField(output_field)

    # Initialize these dictionaries to have the shapefile fields in the
    # original datasource even if we don't pick up a value later

    # This will store the sum/count with index of shapefile attribute
    if shapefile_field is not None:
        shapefile_table = extract_datasource_table_by_key(
            shapefile_uri, shapefile_field)
    else:
        shapefile_table = {global_id_value: 0.0}

    current_iteration_shapefiles = dict([
        (shapefile_id, 0.0) for shapefile_id in shapefile_table.iterkeys()])
    aggregate_dict_values = current_iteration_shapefiles.copy()
    aggregate_dict_counts = current_iteration_shapefiles.copy()
    # Populate the means and totals with something in case the underlying
    # raster doesn't exist for those features.  we use -9999 as a recognizable
    # nodata value.
    for shapefile_id in shapefile_table:
        result_tuple.pixel_mean[shapefile_id] = -9999
        result_tuple.total[shapefile_id] = -9999
        result_tuple.hectare_mean[shapefile_id] = -9999

    pixel_min_dict = dict(
        [(shapefile_id, None) for shapefile_id in shapefile_table.iterkeys()])
    pixel_max_dict = pixel_min_dict.copy()

    # Loop over each polygon and aggregate
    if polygons_might_overlap:
        minimal_polygon_sets = calculate_disjoint_polygon_set(
            shapefile_uri)
    else:
        minimal_polygon_sets = [
            set([feat.GetFID() for feat in shapefile_layer])]

    clipped_band = clipped_raster.GetRasterBand(1)

    for polygon_set in minimal_polygon_sets:
        # add polygons to subset_layer
        for poly_fid in polygon_set:
            poly_feat = shapefile_layer.GetFeature(poly_fid)
            subset_layer.CreateFeature(poly_feat)
        subset_layer_datasouce.SyncToDisk()

        # nodata out the mask
        mask_band = mask_dataset.GetRasterBand(1)
        mask_band.Fill(mask_nodata)
        mask_band = None

        gdal.RasterizeLayer(
            mask_dataset, [1], subset_layer, **rasterize_layer_args)
        mask_dataset.FlushCache()

        # get feature areas
        feature_areas = collections.defaultdict(int)
        for feature in subset_layer:
            # feature = subset_layer.GetFeature(index)
            geom = feature.GetGeometryRef()
            if shapefile_field is not None:
                feature_id = feature.GetField(shapefile_field)
                feature_areas[feature_id] = geom.GetArea()
            else:
                feature_areas[global_id_value] += geom.GetArea()
        subset_layer.ResetReading()
        geom = None

        # Need a complicated step to see what the FIDs are in the subset_layer
        # then need to loop through and delete them
        fid_to_delete = set()
        for feature in subset_layer:
            fid_to_delete.add(feature.GetFID())
        subset_layer.ResetReading()
        for fid in fid_to_delete:
            subset_layer.DeleteFeature(fid)
        subset_layer_datasouce.SyncToDisk()

        current_iteration_attribute_ids = set()

        for mask_offsets, mask_block in iterblocks(mask_uri):
            clipped_block = clipped_band.ReadAsArray(**mask_offsets)

            unique_ids = numpy.unique(mask_block)
            current_iteration_attribute_ids = (
                current_iteration_attribute_ids.union(unique_ids))
            for attribute_id in unique_ids:
                # ignore masked values
                if attribute_id == mask_nodata:
                    continue

                # Consider values which lie in the polygon for attribute_id
                masked_values = clipped_block[
                    (mask_block == attribute_id) &
                    (~numpy.isnan(clipped_block))]
                # Remove the nodata and ignore values for later processing
                masked_values_nodata_removed = (
                    masked_values[~numpy.in1d(
                        masked_values, [raster_nodata]).
                                  reshape(masked_values.shape)])

                # Find the min and max which might not yet be calculated
                if masked_values_nodata_removed.size > 0:
                    if pixel_min_dict[attribute_id] is None:
                        pixel_min_dict[attribute_id] = numpy.min(
                            masked_values_nodata_removed)
                        pixel_max_dict[attribute_id] = numpy.max(
                            masked_values_nodata_removed)
                    else:
                        pixel_min_dict[attribute_id] = min(
                            pixel_min_dict[attribute_id],
                            numpy.min(masked_values_nodata_removed))
                        pixel_max_dict[attribute_id] = max(
                            pixel_max_dict[attribute_id],
                            numpy.max(masked_values_nodata_removed))

                if ignore_nodata:
                    # Only consider values which are not nodata values
                    aggregate_dict_counts[attribute_id] += (
                        masked_values_nodata_removed.size)
                else:
                    aggregate_dict_counts[attribute_id] += masked_values.size

                aggregate_dict_values[attribute_id] += numpy.sum(
                    masked_values_nodata_removed)

        # Initialize the dictionary to have an n_pixels field that contains the
        # counts of all the pixels used in the calculation.
        result_tuple.n_pixels.update(aggregate_dict_counts.copy())
        result_tuple.pixel_min.update(pixel_min_dict.copy())
        result_tuple.pixel_max.update(pixel_max_dict.copy())
        # Don't want to calculate stats for the nodata
        current_iteration_attribute_ids.discard(mask_nodata)
        for attribute_id in current_iteration_attribute_ids:
            result_tuple.total[attribute_id] = (
                aggregate_dict_values[attribute_id])

            # intitalize to 0
            result_tuple.pixel_mean[attribute_id] = 0.0
            result_tuple.hectare_mean[attribute_id] = 0.0

            if aggregate_dict_counts[attribute_id] != 0.0:
                n_pixels = aggregate_dict_counts[attribute_id]
                result_tuple.pixel_mean[attribute_id] = (
                    aggregate_dict_values[attribute_id] / n_pixels)

                # To get the total area multiply n pixels by their area then
                # divide by 10000 to get Ha.  Notice that's in the denominator
                # so the * 10000 goes on the top
                if feature_areas[attribute_id] != 0:
                    result_tuple.hectare_mean[attribute_id] = 10000.0 * (
                        aggregate_dict_values[attribute_id] /
                        feature_areas[attribute_id])

    # Make sure the dataset is closed and cleaned up
    mask_band = None
    gdal.Dataset.__swig_destroy__(mask_dataset)
    mask_dataset = None

    clipped_band = None
    gdal.Dataset.__swig_destroy__(clipped_raster)
    clipped_raster = None

    for filename in [mask_uri, clipped_raster_uri]:
        try:
            os.remove(filename)
        except OSError as error:
            LOGGER.warn(
                "couldn't remove file %s. Exception %s", filename, str(error))

    subset_layer = None
    ogr.DataSource.__swig_destroy__(subset_layer_datasouce)
    subset_layer_datasouce = None
    try:
        shutil.rmtree(layer_dir)
    except OSError as error:
        LOGGER.warn(
            "couldn't remove directory %s.  Exception %s", layer_dir,
            str(error))

    return result_tuple


def calculate_slope(
        dem_dataset_uri, slope_uri, aoi_uri=None, process_pool=None):
    """Create slope raster from DEM raster.

    Follows the algorithm described here:
    http://webhelp.esri.com/arcgiSDEsktop/9.3/index.cfm?TopicName=How%20Slope%20works

    Args:
        dem_dataset_uri (string): a URI to a  single band raster of z values.
        slope_uri (string): a path to the output slope uri in percent.

    Keyword Args:
        aoi_uri (string): a uri to an AOI input
        process_pool: a process pool for multiprocessing

    Returns:
        None
    """
    out_pixel_size = get_cell_size_from_uri(dem_dataset_uri)
    dem_nodata = get_nodata_from_uri(dem_dataset_uri)

    dem_small_uri = temporary_filename(suffix='.tif')
    # cast the dem to a floating point one if it's not already
    dem_float_nodata = float(dem_nodata)

    vectorize_datasets(
        [dem_dataset_uri], lambda x: x.astype(numpy.float32), dem_small_uri,
        gdal.GDT_Float32, dem_float_nodata, out_pixel_size, "intersection",
        dataset_to_align_index=0, aoi_uri=aoi_uri, process_pool=process_pool,
        vectorize_op=False)

    slope_nodata = -9999.0
    new_raster_from_base_uri(
        dem_small_uri, slope_uri, 'GTiff', slope_nodata, gdal.GDT_Float32)
    geoprocessing_core._cython_calculate_slope(
        dem_small_uri, slope_uri)
    calculate_raster_stats_uri(slope_uri)

    os.remove(dem_small_uri)


def clip_dataset_uri(
        source_dataset_uri, aoi_datasource_uri, out_dataset_uri,
        assert_projections=True, process_pool=None, all_touched=False):
    """Clip raster dataset to bounding box of provided vector datasource aoi.

    This function will clip source_dataset to the bounding box of the
    polygons in aoi_datasource and mask out the values in source_dataset
    outside of the AOI with the nodata values in source_dataset.

    Args:
        source_dataset_uri (string): uri to single band GDAL dataset to clip
        aoi_datasource_uri (string): uri to ogr datasource
        out_dataset_uri (string): path to disk for the clipped datset

    Keyword Args:
        assert_projections (boolean): a boolean value for whether the dataset
            needs to be projected
        process_pool: a process pool for multiprocessing
        all_touched (boolean): if true the clip uses the option ALL_TOUCHED=TRUE
            when calling RasterizeLayer for AOI masking.

    Returns:
        None
    """
    source_dataset = gdal.Open(source_dataset_uri)

    band = source_dataset.GetRasterBand(1)
    nodata = band.GetNoDataValue()
    datatype = band.DataType

    if nodata is None:
        nodata = -9999

    gdal.Dataset.__swig_destroy__(source_dataset)
    source_dataset = None

    pixel_size = get_cell_size_from_uri(source_dataset_uri)
    vectorize_datasets(
        [source_dataset_uri], lambda x: x, out_dataset_uri, datatype, nodata,
        pixel_size, 'intersection', aoi_uri=aoi_datasource_uri,
        assert_datasets_projected=assert_projections,
        process_pool=process_pool, vectorize_op=False, all_touched=all_touched)


def create_rat_uri(dataset_uri, attr_dict, column_name):
    """Create a raster attribute table.

    URI wrapper for create_rat.

    Args:
        dataset_uri (string): a GDAL raster dataset to create the RAT for (...)
        attr_dict (dict): a dictionary with keys that point to a primitive type
           {integer_id_1: value_1, ... integer_id_n: value_n}
        column_name (string): a string for the column name that maps the values
    """
    dataset = gdal.Open(dataset_uri, gdal.GA_Update)
    create_rat(dataset, attr_dict, column_name)

    # Make sure the dataset is closed and cleaned up
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None


def create_rat(dataset, attr_dict, column_name):
    """Create a raster attribute table.

    Args:
        dataset: a GDAL raster dataset to create the RAT for (...)
        attr_dict (dict): a dictionary with keys that point to a primitive type
           {integer_id_1: value_1, ... integer_id_n: value_n}
        column_name (string): a string for the column name that maps the values

    Returns:
        dataset (gdal.Dataset): a GDAL raster dataset with an updated RAT
    """
    band = dataset.GetRasterBand(1)
    rat = gdal.RasterAttributeTable()
    rat.SetRowCount(len(attr_dict))

    # create columns
    rat.CreateColumn('Value', gdal.GFT_Integer, gdal.GFU_MinMax)
    rat.CreateColumn(column_name, gdal.GFT_String, gdal.GFU_Name)

    row_count = 0
    for key in sorted(attr_dict.keys()):
        rat.SetValueAsInt(row_count, 0, int(key))
        rat.SetValueAsString(row_count, 1, attr_dict[key])
        row_count += 1

    band.SetDefaultRAT(rat)
    return dataset


def get_raster_properties_uri(dataset_uri):
    """Get width, height, X size, and Y size of the dataset as dictionary.

    Wrapper function for get_raster_properties() that passes in the dataset
    URI instead of the datasets itself

    Args:
        dataset_uri (string): a URI to a GDAL raster dataset

    Returns:
        value (dictionary): a dictionary with the properties stored under
            relevant keys. The current list of things returned is:
            width (w-e pixel resolution), height (n-s pixel resolution),
            XSize, YSize
    """
    dataset = gdal.Open(dataset_uri)
    value = get_raster_properties(dataset)

    # Make sure the dataset is closed and cleaned up
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return value


def get_raster_properties(dataset):
    """Get width, height, X size, and Y size of the dataset as dictionary.

    *This function can be expanded to return more properties if needed*

    Args:
       dataset (gdal.Dataset): a GDAL raster dataset to get the properties from

    Returns:
        dataset_dict (dictionary): a dictionary with the properties stored
            under relevant keys. The current list of things returned is:
            width (w-e pixel resolution), height (n-s pixel resolution),
            XSize, YSize
    """
    dataset_dict = {}
    geo_transform = dataset.GetGeoTransform()
    dataset_dict['width'] = float(geo_transform[1])
    dataset_dict['height'] = float(geo_transform[5])
    dataset_dict['x_size'] = dataset.GetRasterBand(1).XSize
    dataset_dict['y_size'] = dataset.GetRasterBand(1).YSize
    return dataset_dict


def reproject_dataset_uri(
        original_dataset_uri, pixel_spacing, output_wkt, resampling_method,
        output_uri):
    """Reproject and resample GDAL dataset.

    A function to reproject and resample a GDAL dataset given an output
    pixel size and output reference. Will use the datatype and nodata value
    from the original dataset.

    Args:
        original_dataset_uri (string): a URI to a gdal Dataset to written to
            disk
        pixel_spacing: output dataset pixel size in projected linear units
        output_wkt: output project in Well Known Text
        resampling_method (string): a string representing the one of the
            following resampling methods:
            "nearest|bilinear|cubic|cubic_spline|lanczos"
        output_uri (string): location on disk to dump the reprojected dataset

    Returns:
        None
    """
    # A dictionary to map the resampling method input string to the gdal type
    resample_dict = {
        "nearest": gdal.GRA_NearestNeighbour,
        "bilinear": gdal.GRA_Bilinear,
        "cubic": gdal.GRA_Cubic,
        "cubic_spline": gdal.GRA_CubicSpline,
        "lanczos": gdal.GRA_Lanczos
        }

    # Get the nodata value and datatype from the original dataset
    output_type = get_datatype_from_uri(original_dataset_uri)
    out_nodata = get_nodata_from_uri(original_dataset_uri)

    original_dataset = gdal.Open(original_dataset_uri)

    original_wkt = original_dataset.GetProjection()

    # Create a virtual raster that is projected based on the output WKT. This
    # vrt does not save to disk and is used to get the proper projected
    # bounding box and size.
    vrt = gdal.AutoCreateWarpedVRT(
        original_dataset, None, output_wkt, gdal.GRA_Bilinear)

    geo_t = vrt.GetGeoTransform()
    x_size = vrt.RasterXSize  # Raster xsize
    y_size = vrt.RasterYSize  # Raster ysize

    # Calculate the extents of the projected dataset. These values will be used
    # to properly set the resampled size for the output dataset
    (ulx, uly) = (geo_t[0], geo_t[3])
    (lrx, lry) = (geo_t[0] + geo_t[1] * x_size, geo_t[3] + geo_t[5] * y_size)

    gdal_driver = gdal.GetDriverByName('GTiff')

    # Create the output dataset to receive the projected output, with the
    # proper resampled arrangement.
    output_dataset = gdal_driver.Create(
        output_uri, int((lrx - ulx)/pixel_spacing),
        int((uly - lry)/pixel_spacing), 1, output_type,
        options=['BIGTIFF=IF_SAFER'])

    # Set the nodata value for the output dataset
    output_dataset.GetRasterBand(1).SetNoDataValue(float(out_nodata))

    # Calculate the new geotransform
    output_geo = (ulx, pixel_spacing, geo_t[2], uly, geo_t[4], -pixel_spacing)

    # Set the geotransform
    output_dataset.SetGeoTransform(output_geo)
    output_dataset.SetProjection(output_wkt)

    # Perform the projection/resampling
    def reproject_callback(df_complete, psz_message, p_progress_arg):
        """The argument names come from the GDAL API for callbacks."""
        try:
            current_time = time.time()
            if ((current_time - reproject_callback.last_time) > 5.0 or
                    (df_complete == 1.0 and reproject_callback.total_time >= 5.0)):
                LOGGER.info(
                    "ReprojectImage %.1f%% complete %s, psz_message %s",
                    df_complete * 100, p_progress_arg[0], psz_message)
                reproject_callback.last_time = current_time
                reproject_callback.total_time += current_time
        except AttributeError:
            reproject_callback.last_time = time.time()
            reproject_callback.total_time = 0.0

    gdal.ReprojectImage(
        original_dataset, output_dataset, original_wkt, output_wkt,
        resample_dict[resampling_method], 0, 0, reproject_callback,
        [output_uri])

    output_dataset.FlushCache()

    #Make sure the dataset is closed and cleaned up
    gdal.Dataset.__swig_destroy__(output_dataset)
    output_dataset = None
    calculate_raster_stats_uri(output_uri)


def reproject_datasource_uri(original_dataset_uri, output_wkt, output_uri):
    """Reproject OGR DataSource file.

    URI wrapper for reproject_datasource that takes in the uri for the
    datasource that is to be projected instead of the datasource itself.
    This function directly calls reproject_datasource.

    Args:
        original_dataset_uri (string): a uri to an ogr datasource
        output_wkt: the desired projection as Well Known Text
            (by layer.GetSpatialRef().ExportToWkt())
        output_uri (string): the path to where the new shapefile should be
            written to disk.

    Return:
        None
    """
    original_dataset = ogr.Open(original_dataset_uri)
    _ = reproject_datasource(original_dataset, output_wkt, output_uri)


def reproject_datasource(original_datasource, output_wkt, output_uri):
    """Reproject OGR DataSource object.

    Changes the projection of an ogr datasource by creating a new
    shapefile based on the output_wkt passed in.  The new shapefile
    then copies all the features and fields of the original_datasource
    as its own.

    Args:
        original_datasource: an ogr datasource
        output_wkt: the desired projection as Well Known Text
            (by layer.GetSpatialRef().ExportToWkt())
        output_uri (string): the filepath to the output shapefile

    Returns:
        output_datasource: the reprojected shapefile.
    """

    # if this file already exists, then remove it
    if os.path.isfile(output_uri):
        os.remove(output_uri)

    output_sr = osr.SpatialReference()
    output_sr.ImportFromWkt(output_wkt)

    # create a new shapefile from the orginal_datasource
    output_driver = ogr.GetDriverByName('ESRI Shapefile')
    output_datasource = output_driver.CreateDataSource(output_uri)

    # loop through all the layers in the orginal_datasource
    for original_layer in original_datasource:

        # Get the original_layer definition which holds needed attribute values
        original_layer_dfn = original_layer.GetLayerDefn()

        # Create the new layer for output_datasource using same name and
        # geometry type from original_datasource, but different projection
        output_layer = output_datasource.CreateLayer(
            original_layer_dfn.GetName(), output_sr,
            original_layer_dfn.GetGeomType())

        # Get the number of fields in original_layer
        original_field_count = original_layer_dfn.GetFieldCount()

        # For every field, create a duplicate field and add it to the new
        # shapefiles layer
        for fld_index in range(original_field_count):
            original_field = original_layer_dfn.GetFieldDefn(fld_index)
            output_field = ogr.FieldDefn(
                original_field.GetName(), original_field.GetType())
            output_layer.CreateField(output_field)

        original_layer.ResetReading()

        # Get the spatial reference of the original_layer to use in transforming
        original_sr = original_layer.GetSpatialRef()

        # Create a coordinate transformation
        coord_trans = osr.CoordinateTransformation(original_sr, output_sr)

        # Copy all of the features in original_layer to the new shapefile
        error_count = 0
        for original_feature in original_layer:
            geom = original_feature.GetGeometryRef()

            # Transform the geometry into format desired for the new projection
            error_code = geom.Transform(coord_trans)
            if error_code != 0: # error
                # this could be caused by an out of range transformation
                # whatever the case, don't put the transformed poly into the
                # output set
                error_count += 1
                continue

            # Copy original_datasource's feature and set as new shapes feature
            output_feature = ogr.Feature(
                feature_def=output_layer.GetLayerDefn())
            output_feature.SetFrom(original_feature)
            output_feature.SetGeometry(geom)

            # For all the fields in the feature set the field values from the
            # source field
            for fld_index2 in range(output_feature.GetFieldCount()):
                original_field_value = original_feature.GetField(fld_index2)
                output_feature.SetField(fld_index2, original_field_value)

            output_layer.CreateFeature(output_feature)
            output_feature = None

            original_feature = None
        if error_count > 0:
            LOGGER.warn(
                '%d features out of %d were unable to be transformed and are'
                ' not in the output dataset at %s', error_count,
                original_layer.GetFeatureCount(), output_uri)
        original_layer = None

    return output_datasource


def unique_raster_values_uri(dataset_uri):
    """Get list of unique integer values within given dataset.

    Args:
        dataset_uri (string): a uri to a gdal dataset of some integer type

    Returns:
        value (list): a list of dataset's unique non-nodata values
    """
    dataset = gdal.Open(dataset_uri)
    value = unique_raster_values(dataset)

    # Close and clean up dataset
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return value


def unique_raster_values(dataset):
    """Get list of unique integer values within given dataset.

    Args:
        dataset: a gdal dataset of some integer type

    Returns:
        unique_list (list): a list of dataset's unique non-nodata values
    """
    band = dataset.GetRasterBand(1)
    nodata = band.GetNoDataValue()
    n_rows = band.YSize
    unique_values = numpy.array([])
    for row_index in xrange(n_rows):
        array = band.ReadAsArray(0, row_index, band.XSize, 1)[0]
        array = numpy.append(array, unique_values)
        unique_values = numpy.unique(array)

    unique_list = list(unique_values)
    if nodata in unique_list:
        unique_list.remove(nodata)
    return unique_list


def get_rat_as_dictionary_uri(dataset_uri):
    """Get Raster Attribute Table of the first band of dataset as a dictionary.

    Args:
        dataset (string): a GDAL dataset that has a RAT associated with the
            first band

    Returns:
        value (dictionary): a 2D dictionary where the first key is the column
            name and second is the row number
    """
    dataset = gdal.Open(dataset_uri)
    value = get_rat_as_dictionary(dataset)

    # Close and clean up dataset
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return value


def get_rat_as_dictionary(dataset):
    """Get Raster Attribute Table of the first band of dataset as a dictionary.

    Args:
        dataset (gdal.Dataset): a GDAL dataset that has a RAT associated with
            the first band

    Returns:
        rat_dictionary (dictionary): a 2D dictionary where the first key is the
            column name and second is the row number
    """
    band = dataset.GetRasterBand(1)
    rat = band.GetDefaultRAT()
    n_columns = rat.GetColumnCount()
    n_rows = rat.GetRowCount()
    rat_dictionary = {}

    for col_index in xrange(n_columns):
        # Initialize an empty list to store row data and figure out the type
        # of data stored in that column.
        col_type = rat.GetTypeOfCol(col_index)
        col_name = rat.GetNameOfCol(col_index)
        rat_dictionary[col_name] = []

        # Now burn through all the rows to populate the column
        for row_index in xrange(n_rows):
            # This bit of python ugliness handles the known 3 types of gdal
            # RAT fields.
            if col_type == gdal.GFT_Integer:
                value = rat.GetValueAsInt(row_index, col_index)
            elif col_type == gdal.GFT_Real:
                value = rat.GetValueAsDouble(row_index, col_index)
            else:
                # If the type is not int or real, default to a string,
                # I think this is better than testing for a string and raising
                # an exception if not
                value = rat.GetValueAsString(row_index, col_index)

            rat_dictionary[col_name].append(value)

    return rat_dictionary


def reclassify_dataset_uri(
        dataset_uri, value_map, raster_out_uri, out_datatype, out_nodata,
        exception_flag='values_required', assert_dataset_projected=True):
    """Reclassify values in a dataset.

    A function to reclassify values in dataset to any output type. By default
    the values except for nodata must be in value_map.

    Args:
        dataset_uri (string): a uri to a gdal dataset
        value_map (dictionary): a dictionary of values of
            {source_value: dest_value, ...}
            where source_value's type is a postive integer type and dest_value
            is of type out_datatype.
        raster_out_uri (string): the uri for the output raster
        out_datatype (gdal type): the type for the output dataset
        out_nodata (numerical type): the nodata value for the output raster.
            Must be the same type as out_datatype

    Keyword Args:
        exception_flag (string): either 'none' or 'values_required'.
            If 'values_required' raise an exception if there is a value in the
            raster that is not found in value_map
        assert_dataset_projected (boolean): if True this operation will
            test if the input dataset is not projected and raise an exception
            if so.

    Returns:
        nothing

    Raises:
        Exception: if exception_flag == 'values_required' and the value from
           'key_raster' is not a key in 'attr_dict'
    """
    if exception_flag not in ['none', 'values_required']:
        raise ValueError('unknown exception_flag %s', exception_flag)
    values_required = exception_flag == 'values_required'

    nodata = get_nodata_from_uri(dataset_uri)
    value_map_copy = value_map.copy()
    # possible that nodata value is not defined, so test for None first
    # otherwise if nodata not predefined, remap it into the dictionary
    if nodata is not None and nodata not in value_map_copy:
        value_map_copy[nodata] = out_nodata
    keys = sorted(numpy.array(value_map_copy.keys()))
    values = numpy.array([value_map_copy[x] for x in keys])

    def map_dataset_to_value(original_values):
        """Convert a block of original values to the lookup values."""
        if values_required:
            unique = numpy.unique(original_values)
            has_map = numpy.in1d(unique, keys)
            if not all(has_map):
                raise ValueError(
                    'There was not a value for at least the following codes '
                    '%s for this file %s.\nNodata value is: %s' % (
                        str(unique[~has_map]), dataset_uri, str(nodata)))
        index = numpy.digitize(original_values.ravel(), keys, right=True)
        return values[index].reshape(original_values.shape)

    out_pixel_size = get_cell_size_from_uri(dataset_uri)
    vectorize_datasets(
        [dataset_uri], map_dataset_to_value,
        raster_out_uri, out_datatype, out_nodata, out_pixel_size,
        "intersection", dataset_to_align_index=0,
        vectorize_op=False, assert_datasets_projected=assert_dataset_projected,
        datasets_are_pre_aligned=True)


def load_memory_mapped_array(dataset_uri, memory_file, array_type=None):
    """Get the first band of a dataset as a memory mapped array.

    Args:
        dataset_uri (string): the GDAL dataset to load into a memory mapped
            array
        memory_uri (string): a path to a file OR a file-like object that will
            be used to hold the memory map. It is up to the caller to create
            and delete this file.

    Keyword Args:
        array_type: the type of the resulting array, if None defaults
            to the type of the raster band in the dataset

    Returns:
        memory_array (memmap numpy array): a memmap numpy array of the data
            contained in the first band of dataset_uri
    """
    dataset = gdal.Open(dataset_uri)
    band = dataset.GetRasterBand(1)
    n_rows = dataset.RasterYSize
    n_cols = dataset.RasterXSize

    if array_type == None:
        try:
            dtype = _gdal_to_numpy_type(band)
        except KeyError:
            raise TypeError('Unknown GDAL type %s' % band.DataType)
    else:
        dtype = array_type

    memory_array = numpy.memmap(
        memory_file, dtype=dtype, mode='w+', shape=(n_rows, n_cols))

    band.ReadAsArray(buf_obj=memory_array)

    #Make sure the dataset is closed and cleaned up
    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return memory_array


def temporary_filename(suffix=''):
    """Get path to new temporary file that will be deleted on program exit.

    Returns a temporary filename using mkstemp. The file is deleted
    on exit using the atexit register.

    Keyword Args:
        suffix (string): the suffix to be appended to the temporary file

    Returns:
        fname: a unique temporary filename
    """
    file_handle, path = tempfile.mkstemp(suffix=suffix)
    os.close(file_handle)

    def remove_file(path):
        """Function to remove a file and handle exceptions to register
            in atexit."""
        try:
            os.remove(path)
        except OSError:
            # This happens if the file didn't exist, which is okay because
            # maybe we deleted it in a method
            pass

    atexit.register(remove_file, path)
    return path


def temporary_folder():
    """Get path to new temporary folder that will be deleted on program exit.

    Returns a temporary folder using mkdtemp.  The folder is deleted on exit
    using the atexit register.

    Returns:
        path (string): an absolute, unique and temporary folder path.
    """
    path = tempfile.mkdtemp()

    def remove_folder(path):
        """Function to remove a folder and handle exceptions encountered.  This
        function will be registered in atexit."""
        shutil.rmtree(path, ignore_errors=True)

    atexit.register(remove_folder, path)
    return path


class DatasetUnprojected(Exception):
    """An exception in case a dataset is unprojected"""
    pass


class DifferentProjections(Exception):
    """An exception in case a set of datasets are not in the same projection"""
    pass


def assert_datasets_in_same_projection(dataset_uri_list):
    """Assert that provided datasets are all in the same projection.

    Tests if datasets represented by their uris are projected and in
    the same projection and raises an exception if not.

    Args:
        dataset_uri_list (list): (description)

    Returns:
        is_true (boolean): True (otherwise exception raised)

    Raises:
        DatasetUnprojected: if one of the datasets is unprojected.
        DifferentProjections: if at least one of the datasets is in
            a different projection
    """
    dataset_list = [gdal.Open(dataset_uri) for dataset_uri in dataset_uri_list]
    dataset_projections = []

    unprojected_datasets = set()

    for dataset in dataset_list:
        projection_as_str = dataset.GetProjection()
        dataset_sr = osr.SpatialReference()
        dataset_sr.ImportFromWkt(projection_as_str)
        if not dataset_sr.IsProjected():
            unprojected_datasets.add(dataset.GetFileList()[0])
        dataset_projections.append((dataset_sr, dataset.GetFileList()[0]))

    if len(unprojected_datasets) > 0:
        raise DatasetUnprojected(
            "These datasets are unprojected %s" % (unprojected_datasets))

    for index in range(len(dataset_projections)-1):
        if not dataset_projections[index][0].IsSame(
                dataset_projections[index+1][0]):
            LOGGER.warn(
                "These two datasets might not be in the same projection."
                " The different projections are:\n\n'filename: %s'\n%s\n\n"
                "and:\n\n'filename:%s'\n%s\n\n",
                dataset_projections[index][1],
                dataset_projections[index][0].ExportToPrettyWkt(),
                dataset_projections[index+1][1],
                dataset_projections[index+1][0].ExportToPrettyWkt())

    for dataset in dataset_list:
        # Close and clean up dataset
        gdal.Dataset.__swig_destroy__(dataset)
    dataset_list = None
    return True


def get_bounding_box(dataset_uri):
    """Get bounding box where coordinates are in projected units.

    Args:
        dataset_uri (string): a uri to a GDAL dataset

    Returns:
        bounding_box (list):
            [upper_left_x, upper_left_y, lower_right_x, lower_right_y] in
            projected coordinates
    """
    dataset = gdal.Open(dataset_uri)

    geotransform = dataset.GetGeoTransform()
    n_cols = dataset.RasterXSize
    n_rows = dataset.RasterYSize

    bounding_box = [geotransform[0],
                    geotransform[3],
                    geotransform[0] + n_cols * geotransform[1],
                    geotransform[3] + n_rows * geotransform[5]]

    # Close and cleanup dataset
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None

    return bounding_box


def get_datasource_bounding_box(datasource_uri):
    """Get datasource bounding box where coordinates are in projected units.

    Args:
        dataset_uri (string): a uri to a GDAL dataset

    Returns:
        bounding_box (list):
            [upper_left_x, upper_left_y, lower_right_x, lower_right_y] in
            projected coordinates
    """
    datasource = ogr.Open(datasource_uri)
    layer = datasource.GetLayer(0)
    extent = layer.GetExtent()
    # Reindex datasource extents into the upper left/lower right coordinates
    bounding_box = [extent[0],
                    extent[3],
                    extent[1],
                    extent[2]]
    return bounding_box


def resize_and_resample_dataset_uri(
        original_dataset_uri, bounding_box, out_pixel_size, output_uri,
        resample_method):
    """Resize and resample the given dataset.

    Args:
        original_dataset_uri (string): a GDAL dataset
        bounding_box (list): [upper_left_x, upper_left_y, lower_right_x,
            lower_right_y]
        out_pixel_size: the pixel size in projected linear units
        output_uri (string): the location of the new resampled GDAL dataset
        resample_method (string): the resampling technique, one of
            "nearest|bilinear|cubic|cubic_spline|lanczos"

    Returns:
        None
    """
    resample_dict = {
        "nearest": gdal.GRA_NearestNeighbour,
        "bilinear": gdal.GRA_Bilinear,
        "cubic": gdal.GRA_Cubic,
        "cubic_spline": gdal.GRA_CubicSpline,
        "lanczos": gdal.GRA_Lanczos
        }

    original_dataset = gdal.Open(original_dataset_uri)
    original_band = original_dataset.GetRasterBand(1)
    original_nodata = original_band.GetNoDataValue()

    if original_nodata is None:
        original_nodata = -9999

    original_sr = osr.SpatialReference()
    original_sr.ImportFromWkt(original_dataset.GetProjection())

    output_geo_transform = [
        bounding_box[0], out_pixel_size, 0.0, bounding_box[1], 0.0,
        -out_pixel_size]
    new_x_size = abs(
        int(numpy.round((bounding_box[2] - bounding_box[0]) / out_pixel_size)))
    new_y_size = abs(
        int(numpy.round((bounding_box[3] - bounding_box[1]) / out_pixel_size)))

    if new_x_size == 0:
        LOGGER.warn(
            "bounding_box is so small that x dimension rounds to 0; "
            "clamping to 1.")
        new_x_size = 1
    if new_y_size == 0:
        LOGGER.warn(
            "bounding_box is so small that y dimension rounds to 0; "
            "clamping to 1.")
        new_y_size = 1

    # create the new x and y size
    block_size = original_band.GetBlockSize()
    # If the original band is tiled, then its x blocksize will be different
    # than the number of columns
    if original_band.XSize > 256 and original_band.YSize > 256:
        # it makes sense for many functions to have 256x256 blocks
        block_size[0] = 256
        block_size[1] = 256
        gtiff_creation_options = [
            'TILED=YES', 'BIGTIFF=IF_SAFER', 'BLOCKXSIZE=%d' % block_size[0],
            'BLOCKYSIZE=%d' % block_size[1]]

        metadata = original_band.GetMetadata('IMAGE_STRUCTURE')
        if 'PIXELTYPE' in metadata:
            gtiff_creation_options.append('PIXELTYPE=' + metadata['PIXELTYPE'])
    else:
        # it is so small or strangely aligned, use the default creation options
        gtiff_creation_options = []

    create_directories([os.path.dirname(output_uri)])
    gdal_driver = gdal.GetDriverByName('GTiff')
    output_dataset = gdal_driver.Create(
        output_uri, new_x_size, new_y_size, 1, original_band.DataType,
        options=gtiff_creation_options)
    output_band = output_dataset.GetRasterBand(1)

    output_band.SetNoDataValue(original_nodata)

    # Set the geotransform
    output_dataset.SetGeoTransform(output_geo_transform)
    output_dataset.SetProjection(original_sr.ExportToWkt())

    # need to make this a closure so we get the current time and we can affect
    # state
    def reproject_callback(df_complete, psz_message, p_progress_arg):
        """The argument names come from the GDAL API for callbacks."""
        try:
            current_time = time.time()
            if ((current_time - reproject_callback.last_time) > 5.0 or
                    (df_complete == 1.0 and reproject_callback.total_time >= 5.0)):
                LOGGER.info(
                    "ReprojectImage %.1f%% complete %s, psz_message %s",
                    df_complete * 100, p_progress_arg[0], psz_message)
                reproject_callback.last_time = current_time
                reproject_callback.total_time += current_time
        except AttributeError:
            reproject_callback.last_time = time.time()
            reproject_callback.total_time = 0.0

    # Perform the projection/resampling
    gdal.ReprojectImage(
        original_dataset, output_dataset, original_sr.ExportToWkt(),
        original_sr.ExportToWkt(), resample_dict[resample_method], 0, 0,
        reproject_callback, [output_uri])

    # Make sure the dataset is closed and cleaned up
    original_band = None
    gdal.Dataset.__swig_destroy__(original_dataset)
    original_dataset = None

    output_dataset.FlushCache()
    gdal.Dataset.__swig_destroy__(output_dataset)
    output_dataset = None
    calculate_raster_stats_uri(output_uri)


def align_dataset_list(
        dataset_uri_list, dataset_out_uri_list, resample_method_list,
        out_pixel_size, mode, dataset_to_align_index,
        dataset_to_bound_index=None, aoi_uri=None,
        assert_datasets_projected=True, all_touched=False):
    """Create a new list of datasets that are aligned based on a list of
        inputted datasets.

    Take a list of dataset uris and generates a new set that is completely
    aligned with identical projections and pixel sizes.

    Args:
        dataset_uri_list (list): a list of input dataset uris
        dataset_out_uri_list (list): a parallel dataset uri list whose
            positions correspond to entries in dataset_uri_list
        resample_method_list (list): a list of resampling methods for each
            output uri in dataset_out_uri list.  Each element must be one of
            "nearest|bilinear|cubic|cubic_spline|lanczos"
        out_pixel_size: the output pixel size
        mode (string): one of "union", "intersection", or "dataset" which
            defines how the output output extents are defined as either the
            union or intersection of the input datasets or to have the same
            bounds as an existing raster.  If mode is "dataset" then
            dataset_to_bound_index must be defined
        dataset_to_align_index (int): an int that corresponds to the position
            in one of the dataset_uri_lists that, if positive aligns the output
            rasters to fix on the upper left hand corner of the output
            datasets.  If negative, the bounding box aligns the intersection/
            union without adjustment.
        all_touched (boolean): if True and an AOI is passed, the
            ALL_TOUCHED=TRUE option is passed to the RasterizeLayer function
            when determining the mask of the AOI.

    Keyword Args:
        dataset_to_bound_index: if mode is "dataset" then this index is
            used to indicate which dataset to define the output bounds of the
            dataset_out_uri_list
        aoi_uri (string): a URI to an OGR datasource to be used for the
            aoi.  Irrespective of the `mode` input, the aoi will be used
            to intersect the final bounding box.

    Returns:
        None
    """
    last_time = time.time()

    # make sure that the input lists are of the same length
    list_lengths = [
        len(dataset_uri_list), len(dataset_out_uri_list),
        len(resample_method_list)]
    if not reduce(lambda x, y: x if x == y else False, list_lengths):
        raise Exception(
            "dataset_uri_list, dataset_out_uri_list, and "
            "resample_method_list must be the same length "
            " current lengths are %s" % (str(list_lengths)))

    if assert_datasets_projected:
        assert_datasets_in_same_projection(dataset_uri_list)
    if mode not in ["union", "intersection", "dataset"]:
        raise Exception("Unknown mode %s" % (str(mode)))

    if dataset_to_align_index >= len(dataset_uri_list):
        raise Exception(
            "Alignment index is out of bounds of the datasets index: %s"
            "n_elements %s" % (dataset_to_align_index, len(dataset_uri_list)))
    if mode == "dataset" and dataset_to_bound_index is None:
        raise Exception(
            "Mode is 'dataset' but dataset_to_bound_index is not defined")
    if mode == "dataset" and (dataset_to_bound_index < 0 or
                              dataset_to_bound_index >= len(dataset_uri_list)):
        raise Exception(
            "dataset_to_bound_index is out of bounds of the datasets index: %s"
            "n_elements %s" % (dataset_to_bound_index, len(dataset_uri_list)))

    def merge_bounding_boxes(bb1, bb2, mode):
        """Helper function to merge two bounding boxes through union or
            intersection"""
        less_than_or_equal = lambda x, y: x if x <= y else y
        greater_than = lambda x, y: x if x > y else y

        if mode == "union":
            comparison_ops = [
                less_than_or_equal, greater_than, greater_than,
                less_than_or_equal]
        if mode == "intersection":
            comparison_ops = [
                greater_than, less_than_or_equal, less_than_or_equal,
                greater_than]

        bb_out = [op(x, y) for op, x, y in zip(comparison_ops, bb1, bb2)]
        return bb_out

    # get the intersecting or unioned bounding box
    if mode == "dataset":
        bounding_box = get_bounding_box(
            dataset_uri_list[dataset_to_bound_index])
    else:
        bounding_box = reduce(
            functools.partial(merge_bounding_boxes, mode=mode),
            [get_bounding_box(dataset_uri) for dataset_uri in dataset_uri_list])

    if aoi_uri is not None:
        bounding_box = merge_bounding_boxes(
            bounding_box, get_datasource_bounding_box(aoi_uri), "intersection")

    if (bounding_box[0] >= bounding_box[2] or
            bounding_box[1] <= bounding_box[3]) and mode == "intersection":
        raise Exception("The datasets' intersection is empty "
                        "(i.e., not all the datasets touch each other).")

    if dataset_to_align_index >= 0:
        # bounding box needs alignment
        align_bounding_box = get_bounding_box(
            dataset_uri_list[dataset_to_align_index])
        align_pixel_size = get_cell_size_from_uri(
            dataset_uri_list[dataset_to_align_index])

        for index in [0, 1]:
            n_pixels = int(
                (bounding_box[index] - align_bounding_box[index]) /
                float(align_pixel_size))
            bounding_box[index] = \
                n_pixels * align_pixel_size + align_bounding_box[index]

    for original_dataset_uri, out_dataset_uri, resample_method, index in zip(
            dataset_uri_list, dataset_out_uri_list, resample_method_list,
            range(len(dataset_uri_list))):
        current_time = time.time()
        if current_time - last_time > 5.0:
            last_time = current_time
            LOGGER.info(
                "align_dataset_list aligning dataset %d of %d",
                index, len(dataset_uri_list))

        resize_and_resample_dataset_uri(
            original_dataset_uri, bounding_box, out_pixel_size,
            out_dataset_uri, resample_method)

    # If there's an AOI, mask it out
    if aoi_uri is not None:
        first_dataset = gdal.Open(dataset_out_uri_list[0])
        n_rows = first_dataset.RasterYSize
        n_cols = first_dataset.RasterXSize
        gdal.Dataset.__swig_destroy__(first_dataset)
        first_dataset = None

        mask_uri = temporary_filename(suffix='.tif')
        new_raster_from_base_uri(
            dataset_out_uri_list[0], mask_uri, 'GTiff', 255, gdal.GDT_Byte,
            fill_value=0)

        mask_dataset = gdal.Open(mask_uri, gdal.GA_Update)
        mask_band = mask_dataset.GetRasterBand(1)
        aoi_datasource = ogr.Open(aoi_uri)
        aoi_layer = aoi_datasource.GetLayer()
        if all_touched:
            option_list = ["ALL_TOUCHED=TRUE"]
        else:
            option_list = []
        gdal.RasterizeLayer(
            mask_dataset, [1], aoi_layer, burn_values=[1], options=option_list)
        mask_row = numpy.zeros((1, n_cols), dtype=numpy.int8)

        out_dataset_list = [
            gdal.Open(uri, gdal.GA_Update) for uri in dataset_out_uri_list]
        out_band_list = [
            dataset.GetRasterBand(1) for dataset in out_dataset_list]
        nodata_out_list = [
            get_nodata_from_uri(uri) for uri in dataset_out_uri_list]

        for row_index in range(n_rows):
            mask_row = (mask_band.ReadAsArray(
                0, row_index, n_cols, 1) == 0)
            for out_band, nodata_out in zip(out_band_list, nodata_out_list):
                dataset_row = out_band.ReadAsArray(
                    0, row_index, n_cols, 1)
                out_band.WriteArray(
                    numpy.where(mask_row, nodata_out, dataset_row),
                    xoff=0, yoff=row_index)

        # Remove the mask aoi if necessary
        mask_band = None
        gdal.Dataset.__swig_destroy__(mask_dataset)
        mask_dataset = None
        os.remove(mask_uri)

        # Close and clean up datasource
        aoi_layer = None
        ogr.DataSource.__swig_destroy__(aoi_datasource)
        aoi_datasource = None

        # Clean up datasets
        out_band_list = None
        for dataset in out_dataset_list:
            dataset.FlushCache()
            gdal.Dataset.__swig_destroy__(dataset)
        out_dataset_list = None


def assert_file_existance(dataset_uri_list):
    """Assert that provided uris exist in filesystem.

    Verify that the uris passed in the argument exist on the filesystem
    if not, raise an exeception indicating which files do not exist

    Args:
        dataset_uri_list (list): a list of relative or absolute file paths to
            validate

    Returns:
        None

    Raises:
        IOError: if any files are not found
    """
    not_found_uris = []
    for uri in dataset_uri_list:
        if not os.path.exists(uri):
            not_found_uris.append(uri)

    if len(not_found_uris) != 0:
        error_message = (
            "The following files do not exist on the filesystem: " +
            str(not_found_uris))
        raise exceptions.IOError(error_message)


def vectorize_datasets(
        dataset_uri_list, dataset_pixel_op, dataset_out_uri, datatype_out,
        nodata_out, pixel_size_out, bounding_box_mode,
        resample_method_list=None, dataset_to_align_index=None,
        dataset_to_bound_index=None, aoi_uri=None,
        assert_datasets_projected=True, process_pool=None, vectorize_op=True,
        datasets_are_pre_aligned=False, dataset_options=None,
        all_touched=False):
    """Apply local raster operation on stack of datasets.

    This function applies a user defined function across a stack of
    datasets.  It has functionality align the output dataset grid
    with one of the input datasets, output a dataset that is the union
    or intersection of the input dataset bounding boxes, and control
    over the interpolation techniques of the input datasets, if
    necessary.  The datasets in dataset_uri_list must be in the same
    projection; the function will raise an exception if not.

    Args:
        dataset_uri_list (list): a list of file uris that point to files that
            can be opened with gdal.Open.
        dataset_pixel_op (function) a function that must take in as many
            arguments as there are elements in dataset_uri_list.  The arguments
            can be treated as interpolated or actual pixel values from the
            input datasets and the function should calculate the output
            value for that pixel stack.  The function is a parallel
            paradigmn and does not know the spatial position of the
            pixels in question at the time of the call.  If the
            `bounding_box_mode` parameter is "union" then the values
            of input dataset pixels that may be outside their original
            range will be the nodata values of those datasets.  Known
            bug: if dataset_pixel_op does not return a value in some cases
            the output dataset values are undefined even if the function
            does not crash or raise an exception.
        dataset_out_uri (string): the uri of the output dataset.  The
            projection will be the same as the datasets in dataset_uri_list.
        datatype_out: the GDAL output type of the output dataset
        nodata_out: the nodata value of the output dataset.
        pixel_size_out: the pixel size of the output dataset in
            projected coordinates.
        bounding_box_mode (string): one of "union" or "intersection",
            "dataset". If union the output dataset bounding box will be the
            union of the input datasets.  Will be the intersection otherwise.
            An exception is raised if the mode is "intersection" and the
            input datasets have an empty intersection. If dataset it will make
            a bounding box as large as the given dataset, if given
            dataset_to_bound_index must be defined.

    Keyword Args:
        resample_method_list (list): a list of resampling methods
            for each output uri in dataset_out_uri list.  Each element
            must be one of "nearest|bilinear|cubic|cubic_spline|lanczos".
            If None, the default is "nearest" for all input datasets.
        dataset_to_align_index (int): an int that corresponds to the position
            in one of the dataset_uri_lists that, if positive aligns the output
            rasters to fix on the upper left hand corner of the output
            datasets.  If negative, the bounding box aligns the intersection/
            union without adjustment.
        dataset_to_bound_index: if mode is "dataset" this indicates which
            dataset should be the output size.
        aoi_uri (string): a URI to an OGR datasource to be used for the
            aoi.  Irrespective of the `mode` input, the aoi will be used
            to intersect the final bounding box.
        assert_datasets_projected (boolean): if True this operation will
            test if any datasets are not projected and raise an exception
            if so.
        process_pool: a process pool for multiprocessing
        vectorize_op (boolean): if true the model will try to numpy.vectorize
            dataset_pixel_op.  If dataset_pixel_op is designed to use maximize
            array broadcasting, set this parameter to False, else it may
            inefficiently invoke the function on individual elements.
        datasets_are_pre_aligned (boolean): If this value is set to False
            this operation will first align and interpolate the input datasets
            based on the rules provided in bounding_box_mode,
            resample_method_list, dataset_to_align_index, and
            dataset_to_bound_index, if set to True the input dataset list must
            be aligned, probably by raster_utils.align_dataset_list
        dataset_options: this is an argument list that will be
            passed to the GTiff driver.  Useful for blocksizes, compression,
            etc.
        all_touched (boolean): if true the clip uses the option
            ALL_TOUCHED=TRUE when calling RasterizeLayer for AOI masking.

    Returns:
        None

    Raises:
        ValueError: invalid input provided
    """
    if not isinstance(dataset_uri_list, list):
        raise ValueError(
            "dataset_uri_list was not passed in as a list, maybe a single "
            "file was passed in?  Here is its value: %s" %
            (str(dataset_uri_list)))

    if aoi_uri is None:
        assert_file_existance(dataset_uri_list)
    else:
        assert_file_existance(dataset_uri_list + [aoi_uri])

    if dataset_out_uri in dataset_uri_list:
        raise ValueError(
            "%s is used as an output file, but it is also an input file "
            "in the input list %s" % (dataset_out_uri, str(dataset_uri_list)))

    valid_bounding_box_modes = ["union", "intersection", "dataset"]
    if bounding_box_mode not in valid_bounding_box_modes:
        raise ValueError(
            "Unknown bounding box mode %s; should be one of %s",
            bounding_box_mode, valid_bounding_box_modes)

    # Create a temporary list of filenames whose files delete on the python
    # interpreter exit
    if not datasets_are_pre_aligned:
        # Handle the cases where optional arguments are passed in
        if resample_method_list is None:
            resample_method_list = ["nearest"] * len(dataset_uri_list)
        if dataset_to_align_index is None:
            dataset_to_align_index = -1
        dataset_out_uri_list = [
            temporary_filename(suffix='.tif') for _ in dataset_uri_list]
        # Align and resample the datasets, then load datasets into a list
        align_dataset_list(
            dataset_uri_list, dataset_out_uri_list, resample_method_list,
            pixel_size_out, bounding_box_mode, dataset_to_align_index,
            dataset_to_bound_index=dataset_to_bound_index,
            aoi_uri=aoi_uri,
            assert_datasets_projected=assert_datasets_projected,
            all_touched=all_touched)
        aligned_datasets = [
            gdal.Open(filename, gdal.GA_ReadOnly) for filename in
            dataset_out_uri_list]
    else:
        # otherwise the input datasets are already aligned
        aligned_datasets = [
            gdal.Open(filename, gdal.GA_ReadOnly) for filename in
            dataset_uri_list]

    aligned_bands = [dataset.GetRasterBand(1) for dataset in aligned_datasets]

    n_rows = aligned_datasets[0].RasterYSize
    n_cols = aligned_datasets[0].RasterXSize

    output_dataset = new_raster_from_base(
        aligned_datasets[0], dataset_out_uri, 'GTiff', nodata_out,
        datatype_out, dataset_options=dataset_options)
    output_band = output_dataset.GetRasterBand(1)
    block_size = output_band.GetBlockSize()
    # makes sense to get the largest block size possible to reduce the number
    # of expensive readasarray calls
    for current_block_size in [band.GetBlockSize() for band in aligned_bands]:
        if (current_block_size[0] * current_block_size[1] >
                block_size[0] * block_size[1]):
            block_size = current_block_size

    cols_per_block, rows_per_block = block_size[0], block_size[1]
    n_col_blocks = int(math.ceil(n_cols / float(cols_per_block)))
    n_row_blocks = int(math.ceil(n_rows / float(rows_per_block)))

    # If there's an AOI, mask it out
    if aoi_uri is not None:
        mask_uri = temporary_filename(suffix='.tif')
        mask_dataset = new_raster_from_base(
            aligned_datasets[0], mask_uri, 'GTiff', 255, gdal.GDT_Byte,
            fill_value=0, dataset_options=dataset_options)
        mask_band = mask_dataset.GetRasterBand(1)
        aoi_datasource = ogr.Open(aoi_uri)
        aoi_layer = aoi_datasource.GetLayer()
        if all_touched:
            option_list = ["ALL_TOUCHED=TRUE"]
        else:
            option_list = []
        gdal.RasterizeLayer(
            mask_dataset, [1], aoi_layer, burn_values=[1], options=option_list)
        aoi_layer = None
        aoi_datasource = None

    # We only want to do this if requested, otherwise we might have a more
    # efficient call if we don't vectorize.
    if vectorize_op:
        LOGGER.warn("this call is vectorizing which is deprecated and slow")
        dataset_pixel_op = numpy.vectorize(
            dataset_pixel_op, otypes=[_gdal_to_numpy_type(output_band)])

    last_time = time.time()

    last_row_block_width = None
    last_col_block_width = None
    for row_block_index in xrange(n_row_blocks):
        row_offset = row_block_index * rows_per_block
        row_block_width = n_rows - row_offset
        if row_block_width > rows_per_block:
            row_block_width = rows_per_block

        for col_block_index in xrange(n_col_blocks):
            col_offset = col_block_index * cols_per_block
            col_block_width = n_cols - col_offset
            if col_block_width > cols_per_block:
                col_block_width = cols_per_block

            current_time = time.time()
            if current_time - last_time > 5.0:
                LOGGER.info(
                    'raster stack calculation approx. %.2f%% complete',
                    ((row_block_index * n_col_blocks + col_block_index) /
                     float(n_row_blocks * n_col_blocks) * 100.0))
                last_time = current_time

            #This is true at least once since last_* initialized with None
            if (last_row_block_width != row_block_width or
                    last_col_block_width != col_block_width):
                dataset_blocks = [
                    numpy.zeros(
                        (row_block_width, col_block_width),
                        dtype=_gdal_to_numpy_type(band)) for band in aligned_bands]

                if aoi_uri != None:
                    mask_array = numpy.zeros(
                        (row_block_width, col_block_width), dtype=numpy.int8)

                last_row_block_width = row_block_width
                last_col_block_width = col_block_width

            for dataset_index in xrange(len(aligned_bands)):
                aligned_bands[dataset_index].ReadAsArray(
                    xoff=col_offset, yoff=row_offset,
                    win_xsize=col_block_width,
                    win_ysize=row_block_width,
                    buf_obj=dataset_blocks[dataset_index])

            out_block = dataset_pixel_op(*dataset_blocks)

            # Mask out the row if there is a mask
            if aoi_uri is not None:
                mask_band.ReadAsArray(
                    xoff=col_offset, yoff=row_offset,
                    win_xsize=col_block_width,
                    win_ysize=row_block_width,
                    buf_obj=mask_array)
                out_block[mask_array == 0] = nodata_out

            output_band.WriteArray(
                out_block[0:row_block_width, 0:col_block_width],
                xoff=col_offset, yoff=row_offset)

    # Making sure the band and dataset is flushed and not in memory before
    # adding stats
    output_band.FlushCache()
    output_band = None
    output_dataset.FlushCache()
    gdal.Dataset.__swig_destroy__(output_dataset)
    output_dataset = None

    # Clean up the files made by temporary file because we had an issue once
    # where I was running the water yield model over 2000 times and it made
    # so many temporary files I ran out of disk space.
    if aoi_uri is not None:
        mask_band = None
        gdal.Dataset.__swig_destroy__(mask_dataset)
        mask_dataset = None
        os.remove(mask_uri)
    aligned_bands = None
    for dataset in aligned_datasets:
        gdal.Dataset.__swig_destroy__(dataset)
    aligned_datasets = None
    if not datasets_are_pre_aligned:
        # if they weren't pre-aligned then we have temporary files to remove
        for temp_dataset_uri in dataset_out_uri_list:
            try:
                os.remove(temp_dataset_uri)
            except OSError:
                LOGGER.warn("couldn't delete file %s", temp_dataset_uri)
    calculate_raster_stats_uri(dataset_out_uri
)

def get_lookup_from_table(table_uri, key_field):
    """Read table file in as dictionary.

    Creates a python dictionary to look up the rest of the fields in a
    table file indexed by the given key_field.  This function is case
    insensitive to field header names and returns a lookup table with lowercase
    keys.

    Args:
        table_uri (string): a URI to a dbf or csv file containing at
            least the header key_field
        key_field: (description)

    Returns:
        lookup_dict (dict): a dictionary of the form {key_field_0:
            {header_1: val_1_0, header_2: val_2_0, etc.}
            where key_field_n is the lowercase version of the column name.
    """
    table_object = fileio.TableHandler(table_uri)
    raw_table_dictionary = table_object.get_table_dictionary(key_field.lower())

    lookup_dict = {}
    for key, sub_dict in raw_table_dictionary.iteritems():
        key_value = _smart_cast(key)
        # Map an entire row to its lookup values
        lookup_dict[key_value] = (dict(
            [(sub_key, _smart_cast(value)) for sub_key, value in
             sub_dict.iteritems()]))
    return lookup_dict


def get_lookup_from_csv(csv_table_uri, key_field):
    """Read CSV table file in as dictionary.

    Creates a python dictionary to look up the rest of the fields in a
    csv table indexed by the given key_field

    Args:
        csv_table_uri (string): a URI to a csv file containing at
            least the header key_field
        key_field: (description)

    Returns:
        lookup_dict (dict): returns a dictionary of the form {key_field_0:
            {header_1: val_1_0, header_2: val_2_0, etc.}
            depending on the values of those fields
    """
    def u(string):
        if type(string) is StringType:
            return unicode(string, 'utf-8')
        return string

    with open(csv_table_uri, 'rU') as csv_file:
        # attempt to detect excel style csvs like the example here
        # https://docs.python.org/2/library/csv.html#csv.Sniffer
        # the 1024 is a large chunk of the file, presumably enough to
        # either figure out the dialect or go home.
        # Sniffer expects whole lines, so we need to take extra care to return
        # a string that consists of whole lines.
        dialect = csv.Sniffer().sniff('\n'.join(csv_file.readlines(1024)),
                                      delimiters=";,")
        csv_file.seek(0)
        csv_reader = csv.reader(csv_file, dialect=dialect)
        header_row = map(lambda s: u(s), csv_reader.next())
        key_index = header_row.index(key_field)
        # This makes a dictionary that maps the headers to the indexes they
        # represent in the soon to be read lines
        index_to_field = dict(zip(range(len(header_row)), header_row))

        lookup_dict = {}
        for line_num, line in enumerate(csv_reader):
            try:
                key_value = _smart_cast(line[key_index])
            except IndexError as error:
                LOGGER.error('CSV line %s (%s) should have index %s',
                             line_num, line, key_index)
                raise error
            # Map an entire row to its lookup values
            lookup_dict[key_value] = (
                dict([(index_to_field[index], _smart_cast(value))
                      for index, value in zip(range(len(line)), line)]))
        return lookup_dict


def extract_datasource_table_by_key(datasource_uri, key_field):
    """Return vector attribute table of first layer as dictionary.

    Create a dictionary lookup table of the features in the attribute table
    of the datasource referenced by datasource_uri.

    Args:
        datasource_uri (string): a uri to an OGR datasource
        key_field: a field in datasource_uri that refers to a key value
            for each row such as a polygon id.

    Returns:
        attribute_dictionary (dict): returns a dictionary of the
            form {key_field_0: {field_0: value0, field_1: value1}...}
    """
    # Pull apart the datasource
    datasource = ogr.Open(datasource_uri)
    layer = datasource.GetLayer()
    layer_def = layer.GetLayerDefn()

    # Build up a list of field names for the datasource table
    field_names = []
    for field_id in xrange(layer_def.GetFieldCount()):
        field_def = layer_def.GetFieldDefn(field_id)
        field_names.append(field_def.GetName())

    # Loop through each feature and build up the dictionary representing the
    # attribute table
    attribute_dictionary = {}
    for feature_index in xrange(layer.GetFeatureCount()):
        feature = layer.GetFeature(feature_index)
        feature_fields = {}
        for field_name in field_names:
            feature_fields[field_name] = feature.GetField(field_name)
        key_value = feature.GetField(key_field)
        attribute_dictionary[key_value] = feature_fields

    # Explictly clean up the layers so the files close
    layer = None
    datasource = None
    return attribute_dictionary


def get_geotransform_uri(dataset_uri):
    """Get the geotransform from a gdal dataset.

    Args:
        dataset_uri (string): a URI for the dataset

    Returns:
        geotransform: a dataset geotransform list
    """
    dataset = gdal.Open(dataset_uri)
    geotransform = dataset.GetGeoTransform()
    gdal.Dataset.__swig_destroy__(dataset)
    return geotransform


def get_spatial_ref_uri(datasource_uri):
    """Get the spatial reference of an OGR datasource.

    Args:
        datasource_uri (string): a URI to an ogr datasource

    Returns:
        spat_ref: a spatial reference
    """
    shape_datasource = ogr.Open(datasource_uri)
    layer = shape_datasource.GetLayer()
    spat_ref = layer.GetSpatialRef()
    return spat_ref


def copy_datasource_uri(shape_uri, copy_uri):
    """Create a copy of an ogr shapefile.

    Args:
        shape_uri (string): a uri path to the ogr shapefile that is to be
            copied
        copy_uri (string): a uri path for the destination of the copied
            shapefile

    Returns:
        None
    """
    if os.path.isfile(copy_uri):
        os.remove(copy_uri)

    shape = ogr.Open(shape_uri)
    drv = ogr.GetDriverByName('ESRI Shapefile')
    drv.CopyDataSource(shape, copy_uri)


def create_directories(directory_list):
    """Make directories provided in list of path strings.

    This function will create any of the directories in the directory list
    if possible and raise exceptions if something exception other than
    the directory previously existing occurs.

    Args:
        directory_list (list): a list of string uri paths

    Returns:
        None
    """
    for dir_name in directory_list:
        try:
            os.makedirs(dir_name)
        except OSError as exception:
            #It's okay if the directory already exists, if it fails for
            #some other reason, raise that exception
            if (exception.errno != errno.EEXIST and
                    exception.errno != errno.ENOENT):
                raise


def dictionary_to_point_shapefile(dict_data, layer_name, output_uri):
    """Create a point shapefile from a dictionary.

    The point shapefile created is not projected and uses latitude and
        longitude for its geometry.

    Args:
        dict_data (dict): a python dictionary with keys being unique id's that
            point to sub-dictionarys that have key-value pairs. These inner
            key-value pairs will represent the field-value pair for the point
            features. At least two fields are required in the sub-dictionaries,
            All the keys in the sub dictionary should have the same name and
            order. All the values in the sub dictionary should have the same
            type 'lati' and 'long'. These fields determine the geometry of the
            point
            0 : {'lati':97, 'long':43, 'field_a':6.3, 'field_b':'Forest',...},
            1 : {'lati':55, 'long':51, 'field_a':6.2, 'field_b':'Crop',...},
            2 : {'lati':73, 'long':47, 'field_a':6.5, 'field_b':'Swamp',...}
        layer_name (string): a python string for the name of the layer
        output_uri (string): a uri for the output path of the point shapefile

    Returns:
        None
    """
    # If the output_uri exists delete it
    if os.path.isfile(output_uri):
        os.remove(output_uri)
    elif os.path.isdir(output_uri):
        shutil.rmtree(output_uri)

    output_driver = ogr.GetDriverByName('ESRI Shapefile')
    output_datasource = output_driver.CreateDataSource(output_uri)

    # Set the spatial reference to WGS84 (lat/long)
    source_sr = osr.SpatialReference()
    source_sr.SetWellKnownGeogCS("WGS84")

    output_layer = output_datasource.CreateLayer(
        layer_name, source_sr, ogr.wkbPoint)

    # Outer unique keys
    outer_keys = dict_data.keys()

    # Construct a list of fields to add from the keys of the inner dictionary
    field_list = dict_data[outer_keys[0]].keys()

    # Create a dictionary to store what variable types the fields are
    type_dict = {}
    for field in field_list:
        # Get a value from the field
        val = dict_data[outer_keys[0]][field]
        # Check to see if the value is a String of characters or a number. This
        # will determine the type of field created in the shapefile
        if isinstance(val, str):
            type_dict[field] = 'str'
        else:
            type_dict[field] = 'number'

    for field in field_list:
        field_type = None
        # Distinguish if the field type is of type String or other. If Other,
        # we are assuming it to be a float
        if type_dict[field] == 'str':
            field_type = ogr.OFTString
        else:
            field_type = ogr.OFTReal

        output_field = ogr.FieldDefn(field, field_type)
        output_layer.CreateField(output_field)

    # For each inner dictionary (for each point) create a point and set its
    # fields
    for point_dict in dict_data.itervalues():
        latitude = float(point_dict['lati'])
        longitude = float(point_dict['long'])

        geom = ogr.Geometry(ogr.wkbPoint)
        geom.AddPoint_2D(longitude, latitude)

        output_feature = ogr.Feature(output_layer.GetLayerDefn())

        for field_name in point_dict:
            field_index = output_feature.GetFieldIndex(field_name)
            output_feature.SetField(field_index, point_dict[field_name])

        output_feature.SetGeometryDirectly(geom)
        output_layer.CreateFeature(output_feature)
        output_feature = None

    output_layer.SyncToDisk()


def get_dataset_projection_wkt_uri(dataset_uri):
    """Get the projection of a GDAL dataset as well known text (WKT).

    Args:
        dataset_uri (string): a URI for the GDAL dataset

    Returns:
        proj_wkt (string): WKT describing the GDAL dataset project
    """
    dataset = gdal.Open(dataset_uri)
    proj_wkt = dataset.GetProjection()
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None
    return proj_wkt


def unique_raster_values_count(dataset_uri, ignore_nodata=True):
    """Return a dict from unique int values in the dataset to their frequency.

    Args:
        dataset_uri (string): uri to a gdal dataset of some integer type

    Keyword Args:
        ignore_nodata (boolean): if set to false, the nodata count is also
            included in the result

    Returns:
        itemfreq (dict): values to count.
    """
    dataset = gdal.Open(dataset_uri)
    band = dataset.GetRasterBand(1)
    nodata = band.GetNoDataValue()

    itemfreq = collections.defaultdict(int)
    for row_index in range(band.YSize):
        cur_array = band.ReadAsArray(0, row_index, band.XSize, 1)[0]
        for val in numpy.unique(cur_array):
            if ignore_nodata and val == nodata:
                continue
            itemfreq[val] += numpy.count_nonzero(cur_array == val)

    band = None
    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None
    return itemfreq


def rasterize_layer_uri(
        raster_uri, shapefile_uri, burn_values=[], option_list=[]):
    """Rasterize datasource layer.

    Burn the layer from 'shapefile_uri' onto the raster from 'raster_uri'.
    Will burn 'burn_value' onto the raster unless 'field' is not None,
    in which case it will burn the value from shapefiles field.

    Args:
        raster_uri (string): a URI to a gdal dataset
        shapefile_uri (string): a URI to an ogr datasource

    Keyword Args:
        burn_values (list): the equivalent value for burning
            into a polygon.  If empty uses the Z values.
        option_list (list): a Python list of options for the operation.
            Example: ["ATTRIBUTE=NPV", "ALL_TOUCHED=TRUE"]

    Returns:
        None
    """
    dataset = gdal.Open(raster_uri, gdal.GA_Update)
    shapefile = ogr.Open(shapefile_uri)
    layer = shapefile.GetLayer()

    gdal.RasterizeLayer(
        dataset, [1], layer, burn_values=burn_values, options=option_list)

    gdal.Dataset.__swig_destroy__(dataset)
    dataset = None
    shapefile = None


def make_constant_raster_from_base_uri(
        base_dataset_uri, constant_value, out_uri, nodata_value=None,
        dataset_type=gdal.GDT_Float32):
    """Create new gdal raster filled with uniform values.

    A helper function that creates a new gdal raster from base, and fills
    it with the constant value provided.

    Args:
        base_dataset_uri (string): the gdal base raster
        constant_value: the value to set the new base raster to
        out_uri (string): the uri of the output raster

    Keyword Args:
        nodata_value: the value to set the constant raster's nodata
            value to.  If not specified, it will be set to constant_value - 1.0
        dataset_type: the datatype to set the dataset to, default
            will be a float 32 value.

    Returns:
        None
    """
    if nodata_value is None:
        nodata_value = constant_value - 1.0
    new_raster_from_base_uri(
        base_dataset_uri, out_uri, 'GTiff', nodata_value,
        dataset_type)
    base_dataset = gdal.Open(out_uri, gdal.GA_Update)
    base_band = base_dataset.GetRasterBand(1)
    base_band.Fill(constant_value)

    base_band = None
    gdal.Dataset.__swig_destroy__(base_dataset)
    base_dataset = None


def calculate_disjoint_polygon_set(shapefile_uri):
    """Create a list of sets of polygons that don't overlap.

    Determining the minimal number of those sets is an np-complete problem so
    this is an approximation that builds up sets of maximal subsets.

    Args:
        shapefile_uri (string): a uri to an OGR shapefile to process

    Returns:
        subset_list (list): list of sets of FIDs from shapefile_uri
    """
    shapefile = ogr.Open(shapefile_uri)
    shapefile_layer = shapefile.GetLayer()

    poly_intersect_lookup = {}
    for poly_feat in shapefile_layer:
        poly_wkt = poly_feat.GetGeometryRef().ExportToWkt()
        shapely_polygon = shapely.wkt.loads(poly_wkt)
        poly_fid = poly_feat.GetFID()
        poly_intersect_lookup[poly_fid] = {
            'poly': shapely_polygon,
            'prepared': shapely.prepared.prep(shapely_polygon),
            'intersects': set(),
        }
    shapefile_layer.ResetReading()

    for poly_fid in poly_intersect_lookup:
        for intersect_poly_fid in poly_intersect_lookup:
            polygon = poly_intersect_lookup[poly_fid]['prepared']
            if polygon.intersects(
                    poly_intersect_lookup[intersect_poly_fid]['poly']):
                poly_intersect_lookup[poly_fid]['intersects'].add(
                    intersect_poly_fid)

    # Build maximal subsets
    subset_list = []
    while len(poly_intersect_lookup) > 0:
        # sort polygons by increasing number of intersections
        heap = []
        for poly_fid, poly_dict in poly_intersect_lookup.iteritems():
            heapq.heappush(
                heap, (len(poly_dict['intersects']), poly_fid, poly_dict))

        # build maximal subset
        maximal_set = set()
        while len(heap) > 0:
            _, poly_fid, poly_dict = heapq.heappop(heap)
            for maxset_fid in maximal_set:
                if maxset_fid in poly_intersect_lookup[poly_fid]['intersects']:
                    # it intersects and can't be part of the maximal subset
                    break
            else:
                # we made it through without an intersection, add poly_fid to
                # the maximal set
                maximal_set.add(poly_fid)
                # remove that polygon and update the intersections
                del poly_intersect_lookup[poly_fid]
        # remove all the polygons from intersections once they're compuated
        for maxset_fid in maximal_set:
            for poly_dict in poly_intersect_lookup.itervalues():
                poly_dict['intersects'].discard(maxset_fid)
        subset_list.append(maximal_set)
    return subset_list


def distance_transform_edt(
        input_mask_uri, output_distance_uri, process_pool=None):
    """Find the Euclidean distance transform on input_mask_uri and output
    the result as raster.

    Args:
        input_mask_uri (string): a gdal raster to calculate distance from
            the non 0 value pixels
        output_distance_uri (string): will make a float raster w/ same
            dimensions and projection as input_mask_uri where all zero values
            of input_mask_uri are equal to the euclidean distance to the
            closest non-zero pixel.

    Keyword Args:
        process_pool: (description)

    Returns:
        None
    """
    mask_as_byte_uri = temporary_filename(suffix='.tif')
    nodata_mask = get_nodata_from_uri(input_mask_uri)
    out_pixel_size = get_cell_size_from_uri(input_mask_uri)
    nodata_out = 255

    def to_byte(input_vector):
        """converts vector to 1, 0, or nodata value to fit in a byte raster"""
        return numpy.where(
            input_vector == nodata_mask, nodata_out, input_vector != 0)

    # 64 seems like a reasonable blocksize
    blocksize = 64
    vectorize_datasets(
        [input_mask_uri], to_byte, mask_as_byte_uri, gdal.GDT_Byte,
        nodata_out, out_pixel_size, "union",
        dataset_to_align_index=0, assert_datasets_projected=False,
        process_pool=process_pool, vectorize_op=False,
        datasets_are_pre_aligned=True,
        dataset_options=[
            'TILED=YES', 'BLOCKXSIZE=%d' % blocksize,
            'BLOCKYSIZE=%d' % blocksize])

    geoprocessing_core.distance_transform_edt(
        mask_as_byte_uri, output_distance_uri)
    try:
        os.remove(mask_as_byte_uri)
    except OSError:
        LOGGER.warn("couldn't remove file %s", mask_as_byte_uri)


def _next_regular(target):
    """
    Find the next regular number greater than or equal to target.

    Regular numbers are composites of the prime factors 2, 3, and 5.
    Also known as 5-smooth numbers or Hamming numbers, these are the optimal
    size for inputs to FFTPACK.

    This source was taken directly from scipy.signaltools and saves us from
    having to access a protected member in a library that could change in
    future releases:

    https://github.com/scipy/scipy/blob/v0.17.1/scipy/signal/signaltools.py#L211

    Parameters:
        target (int): a positive integer to start to find the next Hamming
            number.

    Returns:
        The next regular number greater than or equal to `target`.
    """
    if target <= 6:
        return target

    # Quickly check if it's already a power of 2
    if not (target & (target-1)):
        return target

    match = float('inf')  # Anything found will be smaller
    p5 = 1
    while p5 < target:
        p35 = p5
        while p35 < target:
            # Ceiling integer division, avoiding conversion to float
            # (quotient = ceil(target / p35))
            quotient = -(-target // p35)

            # Quickly find next power of 2 >= quotient
            p2 = 2**((quotient - 1).bit_length())

            N = p2 * p35
            if N == target:
                return N
            elif N < match:
                match = N
            p35 *= 3
            if p35 == target:
                return p35
        if p35 < match:
            match = p35
        p5 *= 5
        if p5 == target:
            return p5
    if p5 < match:
        match = p5
    return match


def convolve_2d_uri(signal_path, kernel_path, output_path):
    """Convolve 2D kernel over 2D signal.

    Convolves the raster in `kernel_path` over `signal_path`.  Nodata values
    are treated as 0.0 during the convolution and masked to nodata for
    the output result where `signal_path` has nodata.

    Parameters:
        signal_path (string): a filepath to a gdal dataset that's the
            source input.
        kernel_path (string): a filepath to a gdal dataset that's the
            source input.
        output_path (string): a filepath to the gdal dataset
            that's the convolution output of signal and kernel
            that is the same size and projection of signal_path. Any nodata
            pixels that align with `signal_path` will be set to nodata.

    Returns:
        None
    """
    output_nodata = numpy.finfo(numpy.float32).min
    new_raster_from_base_uri(
        signal_path, output_path, 'GTiff', output_nodata, gdal.GDT_Float32,
        fill_value=0)

    signal_nodata = get_nodata_from_uri(signal_path)
    n_rows_signal, n_cols_signal = get_row_col_from_uri(signal_path)
    n_rows_kernel, n_cols_kernel = get_row_col_from_uri(kernel_path)

    # by experimentation i found having the smaller raster to be cached
    # gives the best performance
    if n_rows_signal * n_cols_signal < n_rows_kernel * n_cols_kernel:
        s_path = signal_path
        k_path = kernel_path
    else:
        k_path = signal_path
        s_path = kernel_path

    s_nodata = get_nodata_from_uri(s_path)
    k_nodata = get_nodata_from_uri(k_path)

    signal_ds = gdal.Open(signal_path)
    signal_band = signal_ds.GetRasterBand(1)
    output_ds = gdal.Open(output_path, gdal.GA_Update)
    output_band = output_ds.GetRasterBand(1)

    def _fft_cache(fshape, xoff, yoff, data_block):
        """Helper function to remember the last computed fft.

        Parameters:
            fshape (numpy.ndarray): shape of fft
            xoff,yoff (int): offsets of the data block
            data_block (numpy.ndarray): the 2D array to calculate the FFT
                on if not already calculated.

        Returns:
            fft transformed data_block of fshape size."""
        cache_key = (fshape[0], fshape[1], xoff, yoff)
        if cache_key != _fft_cache.key:
            _fft_cache.cache = numpy.fft.rfftn(data_block, fshape)
            _fft_cache.key = cache_key
        return _fft_cache.cache

    _fft_cache.cache = None
    _fft_cache.key = None

    LOGGER.info('starting convolve')
    last_time = time.time()
    signal_data = {}
    for signal_data, signal_block in iterblocks(s_path):
        last_time = _invoke_timed_callback(
            last_time, lambda: LOGGER.info(
                "convolution operating on signal pixel (%d, %d)",
                signal_data['xoff'], signal_data['yoff']),
            _LOGGING_PERIOD)

        signal_nodata_mask = signal_block == s_nodata
        signal_block[signal_nodata_mask] = 0.0

        for kernel_data, kernel_block in iterblocks(k_path):
            left_index_raster = (
                signal_data['xoff'] - n_cols_kernel / 2 + kernel_data['xoff'])
            right_index_raster = (
                signal_data['xoff'] - n_cols_kernel / 2 +
                kernel_data['xoff'] + signal_data['win_xsize'] +
                kernel_data['win_xsize'] - 1)
            top_index_raster = (
                signal_data['yoff'] - n_rows_kernel / 2 + kernel_data['yoff'])
            bottom_index_raster = (
                signal_data['yoff'] - n_rows_kernel / 2 +
                kernel_data['yoff'] + signal_data['win_ysize'] +
                kernel_data['win_ysize'] - 1)

            # it's possible that the piece of the integrating kernel
            # doesn't even affect the final result, we can just skip
            if (right_index_raster < 0 or
                    bottom_index_raster < 0 or
                    left_index_raster > n_cols_signal or
                    top_index_raster > n_rows_signal):
                continue

            kernel_nodata_mask = (kernel_block == k_nodata)
            kernel_block[kernel_nodata_mask] = 0.0

            # determine the output convolve shape
            shape = (
                numpy.array(signal_block.shape) +
                numpy.array(kernel_block.shape) - 1)

            # add zero padding so FFT is fast
            fshape = [_next_regular(int(d)) for d in shape]

            kernel_fft = numpy.fft.rfftn(kernel_block, fshape)
            signal_fft = _fft_cache(
                fshape, signal_data['xoff'], signal_data['yoff'],
                signal_block)

            # this variable determines the output slice that doesn't include
            # the padded array region made for fast FFTs.
            fslice = tuple([slice(0, int(sz)) for sz in shape])
            # classic FFT convolution
            result = numpy.fft.irfftn(signal_fft * kernel_fft, fshape)[fslice]

            left_index_result = 0
            right_index_result = result.shape[1]
            top_index_result = 0
            bottom_index_result = result.shape[0]

            # we might abut the edge of the raster, clip if so
            if left_index_raster < 0:
                left_index_result = -left_index_raster
                left_index_raster = 0
            if top_index_raster < 0:
                top_index_result = -top_index_raster
                top_index_raster = 0
            if right_index_raster > n_cols_signal:
                right_index_result -= right_index_raster - n_cols_signal
                right_index_raster = n_cols_signal
            if bottom_index_raster > n_rows_signal:
                bottom_index_result -= (
                    bottom_index_raster - n_rows_signal)
                bottom_index_raster = n_rows_signal

            # Add result to current output to account for overlapping edges
            index_dict = {
                'xoff': left_index_raster,
                'yoff': top_index_raster,
                'win_xsize': right_index_raster-left_index_raster,
                'win_ysize': bottom_index_raster-top_index_raster
            }

            current_output = output_band.ReadAsArray(**index_dict)
            potential_nodata_signal_array = signal_band.ReadAsArray(
                **index_dict)
            output_array = numpy.empty(
                current_output.shape, dtype=numpy.float32)

            # read the signal block so we know where the nodata are
            valid_mask = potential_nodata_signal_array != signal_nodata
            output_array[:] = output_nodata
            output_array[valid_mask] = (
                (result[top_index_result:bottom_index_result,
                        left_index_result:right_index_result])[valid_mask] +
                current_output[valid_mask])

            output_band.WriteArray(
                output_array, xoff=index_dict['xoff'],
                yoff=index_dict['yoff'])
    output_band.FlushCache()


def _smart_cast(value):
    """Attempt cast to a float, int, else leave as string.

    Args:
        value: a string or numeric type

    Returns:
        value: new value
    """
    # If it's not a string, don't try to cast it because i got a bug
    # where all my floats were happily cast to ints
    if type(value) != str:
        return value
    for cast_function in [int, float]:
        try:
            return cast_function(value)
        except ValueError:
            pass
    for unicode_type in ['ascii', 'utf-8', 'latin-1']:
        try:
            return value.decode(unicode_type)
        except UnicodeDecodeError:
            pass
    LOGGER.warn("unknown encoding type encountered in _smart_cast: %s" % value)
    return value


def tile_dataset_uri(in_uri, out_uri, blocksize):
    """Resample gdal dataset into tiled raster with blocks of blocksize X
        blocksize.

    Args:
        in_uri (string): dataset to base data from
        out_uri (string): output dataset
        blocksize (int): defines the side of the square for the raster, this
            seems to have a lower limit of 16, but is untested

    Returns:
        None
    """
    dataset = gdal.Open(in_uri)
    band = dataset.GetRasterBand(1)
    datatype_out = band.DataType
    nodata_out = get_nodata_from_uri(in_uri)
    pixel_size_out = get_cell_size_from_uri(in_uri)
    dataset_options = ['TILED=YES', 'BLOCKXSIZE=%d' % blocksize,
                       'BLOCKYSIZE=%d' % blocksize, 'BIGTIFF=IF_SAFER']
    vectorize_datasets(
        [in_uri], lambda x: x, out_uri, datatype_out,
        nodata_out, pixel_size_out, 'intersection',
        resample_method_list=None, dataset_to_align_index=None,
        dataset_to_bound_index=None, aoi_uri=None,
        assert_datasets_projected=False, process_pool=None, vectorize_op=False,
        datasets_are_pre_aligned=False, dataset_options=dataset_options)


def iterblocks(
        raster_uri, band_list=None, largest_block=2**20, astype=None,
        offset_only=False):
    """Iterate across all the memory blocks in the input raster.

    Result is a generator of block location information and numpy arrays.

    This is especially useful when a single value needs to be derived from the
    pixel values in a raster, such as the sum total of all pixel values, or
    a sequence of unique raster values.  In such cases, `raster_local_op`
    is overkill, since it writes out a raster.

    As a generator, this can be combined multiple times with itertools.izip()
    to iterate 'simultaneously' over multiple rasters, though the user should
    be careful to do so only with prealigned rasters.

    Parameters:
        raster_uri (string): The string filepath to the raster to iterate over.
        band_list=None (list of ints or None): A list of the bands for which
            the matrices should be returned. The band number to operate on.
            Defaults to None, which will return all bands.  Bands may be
            specified in any order, and band indexes may be specified multiple
            times.  The blocks returned on each iteration will be in the order
            specified in this list.
        largest_block (int): Attempts to iterate over raster blocks with
            this many elements.  Useful in cases where the blocksize is
            relatively small, memory is available, and the function call
            overhead dominates the iteration.  Defaults to 2**20.  A value of
            anything less than the original blocksize of the raster will
            result in blocksizes equal to the original size.
        astype (list of numpy types): If none, output blocks are in the native
            type of the raster bands.  Otherwise this parameter is a list
            of len(band_list) length that contains the desired output types
            that iterblock generates for each band.
        offset_only (boolean): defaults to False, if True `iterblocks` only
            returns offset dictionary and doesn't read any binary data from
            the raster.  This can be useful when iterating over writing to
            an output.

    Returns:
        If `offset_only` is false, on each iteration, a tuple containing a dict
        of block data and `n` 2-dimensional numpy arrays are returned, where
        `n` is the number of bands requested via `band_list`. The dict of
        block data has these attributes:

            data['xoff'] - The X offset of the upper-left-hand corner of the
                block.
            data['yoff'] - The Y offset of the upper-left-hand corner of the
                block.
            data['win_xsize'] - The width of the block.
            data['win_ysize'] - The height of the block.

        If `offset_only` is True, the function returns only the block data and
            does not attempt to read binary data from the raster.
    """
    dataset = gdal.Open(raster_uri)

    if band_list is None:
        band_list = range(1, dataset.RasterCount + 1)

    ds_bands = [dataset.GetRasterBand(index) for index in band_list]

    block = ds_bands[0].GetBlockSize()
    cols_per_block = block[0]
    rows_per_block = block[1]

    n_cols = dataset.RasterXSize
    n_rows = dataset.RasterYSize

    block_area = cols_per_block * rows_per_block
    # try to make block wider
    if largest_block / block_area > 0:
        width_factor = largest_block / block_area
        cols_per_block *= width_factor
        if cols_per_block > n_cols:
            cols_per_block = n_cols
        block_area = cols_per_block * rows_per_block
    # try to make block taller
    if largest_block / block_area > 0:
        height_factor = largest_block / block_area
        rows_per_block *= height_factor
        if rows_per_block > n_rows:
            rows_per_block = n_rows

    n_col_blocks = int(math.ceil(n_cols / float(cols_per_block)))
    n_row_blocks = int(math.ceil(n_rows / float(rows_per_block)))

    # Initialize to None so a block array is created on the first iteration
    last_row_block_width = None
    last_col_block_width = None

    if astype is not None:
        block_type_list = [astype] * len(ds_bands)
    else:
        block_type_list = [
            _gdal_to_numpy_type(ds_band) for ds_band in ds_bands]

    def _block_gen(queue):
        """Load the next memory block via generator paradigm.

        Parameters:
            queue (Queue.Queue): thread safe queue to return offset_dict and
                results

        Returns:
            None
        """
        for row_block_index in xrange(n_row_blocks):
            row_offset = row_block_index * rows_per_block
            row_block_width = n_rows - row_offset
            if row_block_width > rows_per_block:
                row_block_width = rows_per_block

            for col_block_index in xrange(n_col_blocks):
                col_offset = col_block_index * cols_per_block
                col_block_width = n_cols - col_offset
                if col_block_width > cols_per_block:
                    col_block_width = cols_per_block

                # resize the dataset block cache if necessary
                if (last_row_block_width != row_block_width or
                        last_col_block_width != col_block_width):
                    dataset_blocks = [
                        numpy.zeros(
                            (row_block_width, col_block_width),
                            dtype=block_type) for block_type in
                        block_type_list]

                offset_dict = {
                    'xoff': col_offset,
                    'yoff': row_offset,
                    'win_xsize': col_block_width,
                    'win_ysize': row_block_width,
                }
                result = offset_dict
                if not offset_only:
                    for ds_band, block in zip(ds_bands, dataset_blocks):
                        ds_band.ReadAsArray(buf_obj=block, **offset_dict)
                    result = (result,) + tuple(dataset_blocks)
                queue.put(result)
        queue.put('STOP')  # sentinel indicating end of iteration

    # Make the queue only one element deep so it attempts to load the next
    # block while waiting for the next .next() call.
    block_queue = Queue.Queue(1)
    threading.Thread(target=_block_gen, args=(block_queue,)).start()
    for result in iter(block_queue.get, 'STOP'):
        yield result


def transform_bounding_box(
        bounding_box, base_ref_wkt, new_ref_wkt, edge_samples=11):
    """Transform input bounding box to output projection.

    This transform accounts for the fact that the reprojected square bounding
    box might be warped in the new coordinate system.  To account for this,
    the function samples points along the original bounding box edges and
    attempts to make the largest bounding box around any transformed point
    on the edge whether corners or warped edges.

    Parameters:
        bounding_box (list): a list of 4 coordinates in `base_epsg` coordinate
            system describing the bound in the order [xmin, ymin, xmax, ymax]
        base_ref_wkt (string): the spatial reference of the input coordinate
            system in Well Known Text.
        new_ref_wkt (string): the EPSG code of the desired output coordinate
            system in Well Known Text.
        edge_samples (int): the number of interpolated points along each
            bounding box edge to sample along. A value of 2 will sample just
            the corners while a value of 3 will also sample the corners and
            the midpoint.

    Returns:
        A list of the form [xmin, ymin, xmax, ymax] that describes the largest
        fitting bounding box around the original warped bounding box in
        `new_epsg` coordinate system.
    """
    base_ref = osr.SpatialReference()
    base_ref.ImportFromWkt(base_ref_wkt)

    new_ref = osr.SpatialReference()
    new_ref.ImportFromWkt(new_ref_wkt)

    transformer = osr.CoordinateTransformation(base_ref, new_ref)

    def _transform_point(point):
        """Transform an (x,y) point tuple from base_ref to new_ref."""
        trans_x, trans_y, _ = (transformer.TransformPoint(*point))
        return (trans_x, trans_y)

    # The following list comprehension iterates over each edge of the bounding
    # box, divides each edge into `edge_samples` number of points, then
    # reduces that list to an appropriate `bounding_fn` given the edge.
    # For example the left edge needs to be the minimum x coordinate so
    # we generate `edge_samples` number of points between the upper left and
    # lower left point, transform them all to the new coordinate system
    # then get the minimum x coordinate "min(p[0] ...)" of the batch.
    # points are numbered from 0 starting upper right as follows:
    # 0--3
    # |  |
    # 1--2
    p_0 = numpy.array((bounding_box[0], bounding_box[3]))
    p_1 = numpy.array((bounding_box[0], bounding_box[1]))
    p_2 = numpy.array((bounding_box[2], bounding_box[1]))
    p_3 = numpy.array((bounding_box[2], bounding_box[3]))
    transformed_bounding_box = [
        bounding_fn(
            [_transform_point(
                p_a * v + p_b * (1 - v)) for v in numpy.linspace(
                    0, 1, edge_samples)])
        for p_a, p_b, bounding_fn in [
            (p_0, p_1, lambda p_list: min([p[0] for p in p_list])),
            (p_1, p_2, lambda p_list: min([p[1] for p in p_list])),
            (p_2, p_3, lambda p_list: max([p[0] for p in p_list])),
            (p_3, p_0, lambda p_list: max([p[1] for p in p_list]))]]
    return transformed_bounding_box


def _invoke_timed_callback(
        reference_time, callback_lambda, callback_period):
    """Invoke callback if a certain amount of time has passed.

    This is a convenience function to standardize update callbacks from the
    module.

    Parameters:
        reference_time (float): time to base `callback_period` length from.
        callback_lambda (lambda): function to invoke if difference between
            current time and `reference_time` has exceeded `callback_period`.
        callback_period (float): time in seconds to pass until
            `callback_lambda` is invoked.

    Return:
        `reference_time` if `callback_lambda` not invoked, otherwise the time
        when `callback_lambda` was invoked.
    """
    current_time = time.time()
    if current_time - reference_time > callback_period:
        callback_lambda()
        return current_time
    return reference_time
