PCL:AstrometricSolution:* properties

[nou]

Latest version of PixInsight doesn't write FITS headers with WCS information anymore. But there are new image properties that seems to contain same data than FITS.

PCL:AstrometricSolution:ProjectionSystem - CTYPEi
PCL:AstrometricSolution:LinearTransformationMatrix - PCi_j
PCL:AstrometricSolution:ReferenceCelestialCoordinates - CRVALi
PCL:AstrometricSolution:ReferenceImageCoordinates - CRPIXi
PCL:AstrometricSolution:ReferenceNativeCoordinates - PVi_j

Is this observation correct and can be relied on? When I construct FITS header from these values and pass it into wcslib I get correct RA;DEC.

 

[Juan Conejero]

Your observation is correct, although the orientation of our astrometric solutions is different from the standard FITS WCS orientation, so you'll have to apply a rotation to the transformation matrix in some applications, maybe not in others, depending on FITS WCS compliance.

These properties shouldn't be relied on. They will change when we standardize our spline-based astrometric solutions in the next version of the XISF format specification. The PCL namespace is reserved for properties that we use internally in our implementations and are not intended for public access outside of PixInsight. There is no guarantee of stability for these properties.

 

[nou]

Oh so it is just temporary? Then I will not bother with it. But please consider keeping it. That spline method seems to be really complicated while this method require few matrix and vector operations to get RA;DEC coordinates.

Also another point programs like NINA and KStars can produce xisf files. I think it would be great if they could produce them with correct astrometric solutions while not depending on FITS keywords. And producing spline one is probably not feasible without Gaia DR3.