For a WCS returns False if square image (detector) pixels stay square when projected onto the “plane of intermediate world coordinates” as defined in Greisen & Calabretta 2002, A&A, 395, 1061. It will return True if transformation from image (detector) coordinates to the focal plane coordinates is non-orthogonal or if WCS contains non-linear (e.g., SIP) distortions.
Note
Since this function is concerned only about the transformation “image plane”->”focal plane” and not about the transformation “celestial sphere”->”focal plane”->”image plane”, this function ignores distortions arising due to non-linear nature of most projections.
Let’s denote by C either the original or the reconstructed (from PC and CDELT) CD matrix. is_proj_plane_distorted verifies that the transformation from image (detector) coordinates to the focal plane coordinates is orthogonal using the following check:
Parameters: | wcs : WCS
maxerr : float, optional
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Returns: | distorted : bool |