BaseWCS

class snappl.wcs.BaseWCS

Bases: object

The base class that defines the WCS interface that should be used elsewhere.

Code outside this module should only call methods that are defined in this class. This class doesn’ta ctually do antyhing, however; to actually get a working WCS, you need to instantiate a subclass.

Methods Summary

from_header(header)	Create an object from a FITS header.
get_astropy_wcs([readonly, degree])	Return an astropy.wcs.WCS object, if possible.
get_galsim_wcs()	Return a glasim.AstropyWCS object, if possible.
pixel_to_world(x, y)	Go from (x, y) coordinates to ICRS (ra, dec)
to_fits_header()	Return an astropy.io.fits.Header object, if possible, with the WCS in it.
world_to_pixel(ra, dec)	Go from (ra, dec) coordinates to (x, y)

Methods Documentation

classmethod from_header(header)

Create an object from a FITS header.

May not be implemented for all subclasses.

Parameters:

header (astropi.io.fits.Header or dict) – Something that an astropy WCS is able to create itself from.

Return type:

An object of the class this class method was called on.

get_astropy_wcs(readonly=True, degree=None)

Return an astropy.wcs.WCS object, if possible.

Parameters:

• readonly (bool, default True) – If True, you are promising not to modify the WCS you get back! If you’re going to modify it, set readonly to False. (For some subclasses, this doesn’t actually change behavior.)

• degree (int) – The degree of the astropy WCS used to approximate the WCS in the object. The default is subclass-dependent. Ignored by some subclasses.

For some subclasses, this astropy.wcs.WCS may only be an approximation of the true WCS represented by the object.

get_galsim_wcs()

Return a glasim.AstropyWCS object, if possible.

pixel_to_world(x, y)

Go from (x, y) coordinates to ICRS (ra, dec)

Parameters:

• x (float or sequence of float) – The x position on the image. The center of the lower-left pixel is at x=0.0

• y (float or sequence of float) – The y position on the image. The center of the lower-left pixle is y=0.0

Returns:

• ra, dec (floats or arrays of floats, decimal degrees)

• You will get back two floats if x an y were floats. If x and

• y were lists (or other sequences), you will get back two numpy

• arrays of floats.

to_fits_header()

Return an astropy.io.fits.Header object, if possible, with the WCS in it.

world_to_pixel(ra, dec)

Go from (ra, dec) coordinates to (x, y)

Parameters:

• ra (float or sequence of float) – RA in decimal degrees

• dec (float or sequence of float) – Dec in decimal degrees

Returns:

• x, y (floats or arrays of floats)

• Pixel position on the image; the center of the lower-left pixel is (0.0, 0.0).

• If ra and dec were floats, x and y are floats. If ra and dec

• were sequences of floats, x and y will be numpy arrays of floats.