def proj_plane_pixel_area(wcs):
 psm = wcs.celestial.pixel_scale_matrix
 if (psm.shape != (2, 2)):
  raise ValueError(u'Pixel area is defined only for 2D pixels.')
 return np.abs(np.linalg.det(psm))

def proj_plane_pixel_area ( wcs ) : psm = wcs . celestial . pixel_scale_matrix if ( psm . shape != ( 2 , 2 ) ) : raise ValueError ( u'Pixel area is defined only for 2D pixels.' ) return np . abs ( np . linalg . det ( psm ) )
for a **celestial** wcs returns pixel area of the image pixel at the crpix location once it is projected onto the "plane of intermediate world coordinates" as defined in greisen & calabretta 2002 .