skytopix: Coordinate transformation from sky coordinates

This task allows a user to perform coordinate transformations with the full WCS and distortion model on source positions from sky coordinates to the WCS defined by an image. This task serves as a replacement for the IRAF.STSDAS task ‘rd2xy’, albeit with the added capability of understanding the full distortion model provided in the headers of images updated for use with astrodrizzle and tweakreg.

skytopix - A module to perform coordinate transformation from sky to pixel coordinates.

License:

http://www.stsci.edu/resources/software_hardware/pyraf/LICENSE

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 from input image

dec : string, optional

Dec from input image

coordfile : str, optional

full filename with path of file with sky coordinates

colnames : str, optional

comma separated list of column names from ‘coordfile’ files containing x,y coordinates, respectively. Will default to first two columns if None are specified. Column names for ASCII files will use ‘c1’,’c2’,... convention.

separator : str, optional

non-blank separator used as the column delimiter in the coords file

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 module performs a full distortion-corrected coordinate transformation based on all WCS keywords and any recognized distortion keywords from the input image header.

Usage

It can be called from within Python using the syntax:

>>> from drizzlepac import skytopix
>>> x,y = skytopix.rd2xy("input_flt.fits[sci,1]","00:22:36.79","-72:4:9.0")

EXAMPLES

1. The following command will transform the position 00:22:36.79 -72:4:9.0 into a

   position on the image ‘input_flt.fits[sci,1]’ using:

   >>> from drizzlepac import skytopix
   >>> x,y = skytopix.rd2xy("input_file_flt.fits[sci,1]", "00:22:36.79","-72:4:9.0")
   

2. The set of sky positions from ‘input_flt.fits[sci,1]’ stored as

   the 3rd and 4th columns from the ASCII file ‘radec_sci1.dat’ will be transformed and written out to ‘xy_sci1.dat’ using:

   >>> from drizzlepac import skytopix
   >>> x,y = skytopix.rd2xy("input_flt.fits[sci,1]", coordfile='radec_sci1.dat',
       colnames=['c3','c4'], output="xy_sci1.dat")
   

drizzlepac.skytopix.rd2xy(input, ra=None, dec=None, coordfile=None, colnames=None, precision=6, output=None, verbose=True)

Primary interface to perform coordinate transformations from pixel to sky coordinates using STWCS and full distortion models read from the input image header.