imaginglss.utils.wcs_simplezea module

Python routines to apply world-coordinate system transformations based on the simpler ZEA projection used SFD98 milky way dust map

This code is designed to be light-weight, and specialized. The general ZEA projection is UNSUPPORTED. We handle two special cases

• CRVAL = -90 -90 (south)
• CRVAL = 90 90 (north)

The ZEA projection is described in http://fits.gsfc.nasa.gov/registry/tpvwcs/tpv.html and in: “Representations of celestial coordinates in FITS” Calabretta, M. R., and Greisen, E. W., Astronomy & Astrophysics, 395, 1077-1122, 2002.

imaginglss.utils.wcs_simplezea.ang2pix(coord, SCALE, CRPIX, NSGP)

Convert RA, DEC to x,y, with simple ZEA transformation

A simplified version of the ZEA Transform from coord = (ra, dec) to pixel xy coordinate according the the WCS header.

Obviously PV distortion is not supported.

No checking is performed if a given RA, DEC lies outside the range.

Parameters:

coord : array_like

coord = (RA, DEC), RA and DEC (in decimal degrees, vectorized)

SCALE : int

scaling factor

CRPIX : array_like

center pixel number of x, y

NSGP: int

+1 for North, -1 for Sourth.

Notes

Look up Section 5.?.? of

http://www.aanda.org/articles/aa/pdf/2002/45/aah3860.pdf

Although the source code in

https://code.google.com/p/astropysics/source/browse/astropysics/extinct.py

maybe a better explanation of what is done.

The transformation is used by SFD98 dust maps.

imaginglss.utils.wcs_simplezea.pix2ang(xy, SCALE, CRPIX, NSGP)

Convert x, y to RA, DEC with simple ZEA transformation.

See ang2pix()

imaginglss.utils.wcs_simplezea.ang2pix_hdr(coord, hdr, zero_offset=True)

Apply forward (ra,dec)->(x,y) simple ZEA transformation

A convenience function for calling ang2pix, with the transformations described in a dictionary in the usual FITS header style for WCS transformations.

Parameters:

coord : array_like

(ra, dec), RA and DEC (in decimal degrees, vectorized)

hdr : dict

WCS header as a dictionary

zero_offset : boolean, optional,

If True, the routine returns 0-indexed pixel coordinates (useful in Python or C) while if it is False pixels run from 1 (as in Fortran).

Returns:

xy : array_like

xy = (x, y) pixel numbers.

imaginglss.utils.wcs_simplezea.pix2ang_hdr(xy, hdr, zero_offset=True)

Apply backward (x,y)->(ra,dec) simple ZEA transformation

See ang2pix_hdr()