def chip_footprint_polygon(header, hdulist):
"""Create a Mongo-compatible polygon representing the chip footprint
in equatorial cordinates. The polygon is a length-4 list, populated
with length-2 lists of RA, Dec vertices.
"""
wcs = astropy.wcs.WCS(header=header, fobj=hdulist)
footprint = wcs.calc_footprint(header=header)
footprint_lst = footprint.tolist() # cast as a list of floats
return footprint_lst
def add_footprint_from_wcs(self, mosaic_name, wcs):
"""Create a footprint from the WCS embedded in a ``astropy.io.fits``
header for the named (pre-existing) mosaic document.
The footprint is stored under the field ``footprint`` in the mosaic's
document.
In a sense, this is an attempt to persist a WCS instance. Note that
we only save a subset of the astropy.wcs data; that is, we're built
around simple WCS with no PV, etc. This could be fixed though...
.. note:: By default astropy.wcs is 1 based (ie, origins of CRPIX are
1 and not zero; may need to subtract 1 from crpix when used in
numpy arrays
Parameters
----------
mosaic_name : str
Name of the mosaic (the ``_id`` field for the document).
wcs : :class:`astropy.wcs.WCS` instance
WCS for the mosaic.
"""
doc = {}
doc['naxis'] = (wcs._naxis1, wcs._naxis2)
doc['crpix'] = tuple(wcs.wcs.crpix) # (CRPIX1, CRPIX2)
doc['crval'] = tuple(wcs.wcs.crval) # (CRVAL1, CRVAL2)
doc['ctype'] = tuple(wcs.wcs.ctype)
if wcs.wcs.has_cd():
cd = []
for (cdi, cdj) in wcs.wcs.cd:
cd.append([cdi, cdj])
doc['cd'] = cd
try:
doc['cdelt'] = tuple(wcs.wcs.cdelt)
except:
pass
try:
doc['crota'] = tuple(wcs.wcs.crota)
except:
pass
# Make footprint polygon, cast to a list
raDecFootprintArray = wcs.calc_footprint()
raDecFootprint = []
for (ra, dec) in raDecFootprintArray:
raDecFootprint.append([ra, dec])
doc['radec_poly'] = raDecFootprint
# Add footprint to mosaic document
self.set(mosaic_name, "footprint", doc)
def get_image_corners(wcs):
"""
Return the image corners as a list, given a valid WCS object, extracted from the image.
Corners are listed clockwise from the lower left corner.
"""
return list(wcs.calc_footprint())