proj_plane_pixel_area¶
- astropy.wcs.utils.proj_plane_pixel_area(wcs)[source]¶
For a celestial WCS (see
astropy.wcs.WCS.celestial
) returns pixel area of the image pixel at theCRPIX
location once it is projected onto the “plane of intermediate world coordinates” as defined in Greisen & Calabretta 2002, A&A, 395, 1061.Note
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.
Note
In order to compute the area of pixels corresponding to celestial axes only, this function uses the
celestial
WCS object of the inputwcs
. This is different from theproj_plane_pixel_scales
function that computes the scales for the axes of the input WCS itself.- Parameters:
- wcs
WCS
A world coordinate system object.
- wcs
- Returns:
- Raises:
ValueError
Pixel area is defined only for 2D pixels. Most likely the
cd
matrix of thecelestial
WCS is not a square matrix of second order.
Notes
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.