Manual entry of Astrometric Solution

Derek Warltier

I am trying to process some HST data of the Tadpole Galaxy and having difficulty with the astrometric solution.  The data is in two sets, that should form a 1*2 mosaic, which I need in order to fill in the chip gap in the ACS camera.  The frames are about 3 arc-minutes across and have the RA and Dec embedded in the FITS header.  However, there are not enough stars in the Gaia database to to be able to plate-solve the images using image solver, so I am trying to enter all the data manually (using Mike Cranfield's batch FITS keyword script).  I have added the Focal length, pixel size and start and end times, but I am still getting a "no astrometric solution" error when I try to run Mosiac by Coordinates.  Is there a complete list of FITS keywords that constitute a complete astrometric solution and a guide as to how to calculate these manually?

BlockHead

No...that isn't how the astrometric solution works. 

I don't think you are using the right tool.

You should be Aligning By Coordinates (in scripts). PixInsight should be able to interpret the existing astrometic solution that is provided in the HST data (the WCS which is a whole bunch of coefficients, not just focal length and pixel size). I did this very thing with JWST data. 

-the Blockhead

Derek Warltier

Thanks.  I figured that my major problem was that I was deleting the "extraneous" frames before saving the FITS files as .xisf files.  By saving the FITS files as .xisf files without deleting the extra frames, the .xisf retains the entire astrometric solution.  Now, I just have to use processes and scripts that will not delete the astrometric solution.  No dynamic crop or rotation until last thing.  I did submit a suggestion to have dynamic crop updated to recalculate the astrometric solution.