Error in wcs.py

[Russell-Ryan]

The line 870+ of wcs.py to reference the document https://trs.jpl.nasa.gov/bitstream/handle/2014/40409/JPL%20Pub%2007-3%20%20w%20Errata.pdf?sequence=3&isAllowed=y

However, the equations coded up seem to be different from what is in the above document. If you re-index the angles as l0, l1, l2, l3 (and similarly for phi) and assuming that $\lambda_{-1}=\lambda_{3}$ (in the notation of the document), then the 870 should become:

area=np.abs((l1-l3)(np.sin(phi0)-np.sin(phi2)) + (l0-l2)(np.sin(phi3)-np.sin(phi1)))/2.

This gives correct pixel areas.

[mcara]

Just to note, the code referred to in the above comment is:

gwcs/gwcs/wcs.py

Lines 870 to 877 in f6098a6

	l1, phi1 = np.deg2rad(self.__call__(*(crpix - 0.5)))
	l2, phi2 = np.deg2rad(self.__call__(*(crpix + [-0.5, 0.5])))
	l3, phi3 = np.deg2rad(self.__call__(*(crpix + 0.5)))
	l4, phi4 = np.deg2rad(self.__call__(*(crpix + [0.5, -0.5])))
	area = np.abs(0.5 * ((l4 - l2) * np.sin(phi1) +
	(l1 - l3) * np.sin(phi2) +
	(l2 - l4) * np.sin(phi3) +
	(l3 - l2) * np.sin(phi4)))