**skytopix** transforms source positions given as RA, Dec values into 
pixel positions on the image based on the WCS information and any recognized 
distortion keywords contained in the input image header. 

Examples
--------
This task can be run from either the TEAL GUI, or from the Python command-line. 
These examples illustrate the syntax that can be used to run the task in a 
couple of common modes.

1. Run the task using the TEAL GUI under PyRAF:

    >>> import drizzlepac 
    >>> epar skytopix

2. Convert a single sky position (0:22:07.0088,-72:03:05.429) 
    from a calibrated ACS image (j94f05bgq\_flt.fits) into a 
    pixel position (X,Y) without using the TEAL GUI:

  >>> from drizzlepac import skytopix
  >>> x,y = skytopix.rd2xy("j8bt06nyq_flt.fits[sci,1]", 
                        '0:22:07.0088', '-72:03:05.429')

3. Convert a list of (undistorted) sky positions from the file, 
    'radec.dat' for a calibrated ACS image (j8bt06nyq_flt.fits)
     into distorted pixel positions, and write out the result to 
     the file 'xypos.dat' without using the TEAL GUI:

  >>> x,y = skytopix.rd2xy("j8bt06nyq_flt.fits[sci,1]", coordfile="radec.dat",
            output="xypos.dat")


Parameters
----------
    input : str
        full filename with path of input image, an extension name
        ['sci',1] should be provided if input is a multi-extension
        FITS file.

Optional Parameters
-------------------
    ra : string, optional
        RA position in either decimal degrees or HMS format 
        (with or without ':') like '19:10:50.337406303' or '19 10 50.337406303' 
    dec : string, optional
        Dec position in either decimal degrees or HMS format 
        (with or without ':') like '-60:2:22.186557409' or '-60 2 22.186557409'
    coordfile : str, optional
        full filename with path of file with sky coordinates
    colnames : str, optional
        comma separated list of column names from 'coordfile' file 
        containing sky coordinates, respectively. Will default to 
        first two columns if None are specified. Column names for ASCII
        files will use 'c1','c2',... convention.
    precision : int, optional
        Number of floating-point digits in output values 
    output : str, optional
        Name of output file with results, if desired
    verbose : bool
        Print out full list of transformation results (default: False)
Returns
--------
    x : float
        X position of pixel. If more than 1 input value, then it will be a 
        numpy array. 
    y : float
        Y position of pixel. If more than 1 input value, then it will be a 
        numpy array.


Notes
-----
This task performs a full distortion-correction coordinate transformation 
based on all WCS keywords and any recognized distortion keywords from the 
input image header. The transformation recognizes the conventions for 
describing distortion implemented as part of the SIP and Paper IV conventions
used with AstroDrizzle.  Input images can be updated to use these conventions 
through the use of the 'updatewcs' module the STWCS package. 


See Also
--------
stwcs
