is_proj_plane_distorted#
- astropy.wcs.utils.is_proj_plane_distorted(wcs, maxerr=1e-05)[source]#
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 returnTrue
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
andCDELT
) 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:\[\left \| \frac{C \cdot C^{\mathrm{T}}} {| det(C)|} - I \right \|_{\mathrm{max}} < \epsilon .\]- Parameters:
- Returns: