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# Source code for pywws.calib

    """
    Calibrate raw weather station data
    ==================================

    This module allows adjustment of raw data from the weather station as
    part of the 'processing' step (see :doc:`pywws.Process`). For example,
    if you have fitted a funnel to double your rain gauge's collection
    area, you can write a calibration routine to double the rain value.

    The default calibration does two things:
        #. Generate relative atmospheric pressure.
        #. Remove invalid wind direction values.
    Any user calibration you write must also do these.

    Writing your calibration module
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    Firstly, decide where you want to keep your module. Like your text and
    graph templates, it's best to keep it separate from the pywws code, so
    it isn't affected by pywws upgrades. I suggest creating a ``modules``
    directory in the same place as your ``templates`` directory.

    Create a plain text file in your ``modules`` directory, e.g.
    ``calib.py`` and copy the following text into it::

        class Calib(object):
            def __init__(self, params):
                self.pressure_offset = eval(params.get('fixed', 'pressure offset'))
            def calib(self, raw):
                result = dict(raw)
                # sanitise data
                if result['wind_dir'] is not None and result['wind_dir'] >= 16:
                    result['wind_dir'] = None
                # calculate relative pressure
                result['rel_pressure'] = raw['abs_pressure'] + self.pressure_offset
                return result

    The :class:`Calib` class has two methods. :py:meth:`Calib.__init__` is
    the constructor and is a good place to set any constants you need.
    :py:meth:`Calib.calib` generates a single set of 'calibrated' data
    from a single set of 'raw' data. There are a few rules to follow when
    writing this method:

        - Make sure you include the line ``result = dict(raw)``, which
          copies all the raw data to your result value, at the start.

        - Don't modify any of the raw data.

        - Make sure you set ``result['rel_pressure']``.

        - Don't forget to ``return`` the result at the end.

    When you've finished writing your calibration module you can get pywws
    to use it by putting its location in your ``weather.ini`` file. It
    goes in the ``[paths]`` section, as shown in the example below::

        [paths]
        work = /tmp/weather
        templates = /home/jim/weather/templates/
        graph_templates = /home/jim/weather/graph_templates/
        user_calib = /home/jim/weather/modules/usercalib

    Note that the ``user_calib`` value need not include the ``.py`` at the
    end of the file name.

    """

    __docformat__ = "restructuredtext en"

    from datetime import datetime, timedelta
    import logging
    import os
    import sys

    class DefaultCalib(object):
        """Default calibration class.

        This class sets the relative pressure, using a pressure offset
        read from the weather station, and 'sanitises' the wind direction
        value. This is the bare minimum 'calibration' required.

        """
        def __init__(self, params):
            self.pressure_offset = eval(params.get('fixed', 'pressure offset'))
        def calib(self, raw):
            result = dict(raw)
            # sanitise data
            if result['wind_dir'] is not None and result['wind_dir'] >= 16:
                result['wind_dir'] = None
            # calculate relative pressure
            result['rel_pressure'] = raw['abs_pressure'] + self.pressure_offset
            return result

    usercalib = None

    class Calib(object):
        """Calibration class that implements default or user calibration.

        Other pywws modules use this method to create a calibration
        object. The constructor creates either a default calibration
        object or a user calibration object, depending on the
        ``user_calib`` value in the ``[paths]`` section of the ``params``
        parameter. It then adopts the calibration object's
        :py:meth:`calib` method as its own.

        """
        calibrator = None
        def __init__(self, params):
            global usercalib
            self.logger = logging.getLogger('pywws.Calib')
            if not Calib.calibrator:
                user_module = params.get('paths', 'user_calib', None)
                if user_module:
                    self.logger.info('Using user calibration')
                    path, module = os.path.split(user_module)
                    sys.path.insert(0, path)
                    module = os.path.splitext(module)[0]
                    usercalib = __import__(
                        module, globals(), locals(), ['Calib'])
                    Calib.calibrator = usercalib.Calib(params)
                else:
                    self.logger.info('Using default calibration')
                    Calib.calibrator = DefaultCalib(params)
            self.calib = Calib.calibrator.calib

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