For a celestial WCS (see
astropy.wcs.WCS.celestial) returns pixel area of the image pixel at the
CRPIXlocation once it is projected onto the “plane of intermediate world coordinates” as defined in Greisen & Calabretta 2002, A&A, 395, 1061.
This function is concerned only about the transformation “image plane”->”projection plane” and not about the transformation “celestial sphere”->”projection plane”->”image plane”. Therefore, this function ignores distortions arising due to non-linear nature of most projections.
In order to compute the area of pixels corresponding to celestial axes only, this function uses the
celestialWCS object of the input
wcs. This is different from the
proj_plane_pixel_scalesfunction that computes the scales for the axes of the input WCS itself.
A world coordinate system object.
Pixel area is defined only for 2D pixels. Most likely the
cdmatrix of the
celestialWCS is not a square matrix of second order.
Depending on the application, square root of the pixel area can be used to represent a single pixel scale of an equivalent square pixel whose area is equal to the area of a generally non-square pixel.