is_proj_plane_distorted¶

astropy.wcs.utils.
is_proj_plane_distorted
(wcs, maxerr=1e05)[source] [edit on github]¶ 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 nonorthogonal or if WCS contains nonlinear (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 nonlinear 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:  wcs :
WCS
World coordinate system object
 maxerr : float, optional
Accuracy to which the CD matrix, normalized such that \(det(CD)=1\), should be close to being an orthogonal matrix as described in the above equation (see \(\epsilon\)).
Returns:  wcs :