On Sat, Jul 23, 2022 at 03:37 PM, Ray Gralak wrote:

I don't know how Pinpoint does it either, but it is obvious how it could be done dynamically without a model.

The reference is the star catalog that is being used. Once the app finds the approximate center RA/Dec, it could build a map of the distortion by looking at the error between each star's position in the image versus its expected position given its coordinates in the catalog. The display of this error map would be the image's distortion.

-Ray

How would this be any more accurate than astap (without distortion correction)?  It seems that with or without distortion the platesolve would be able to determine precisely the RA/Dec coordinates of the center of the frame. Considering any detrimental impact from distortion would presumably be centered precisely around the center. (Yes, I'm using Roland's definition of distortion for this logic).  

It would be interesting to hear Han's take on this aspect of ASTAP.

EDIT: I'm most interested on whether it would even make a difference for a 10 min unguided exposure. I.e. a practical use scenario.