ASTAP solving images upside down?

[James J]

Not sure why but astap (2024.08.29) seems to be opening images upside down and then solving them correctly but as a result of the flip the rotation angle is then wrong.
The attached file opens flipped and solves with what look like the correct coordinates but it returns the rotation angle as -45.19. Nova.astrometry returns comparable coordinates but a rotation angle of 308deg.

If I save the coords and annotate the image in pixinsight the annotation is flipped.

[han.k]

Hi James,

The orientation displayed can be adapted in the viewer menu. See attached screenshot, options flipped vertical, horizontal.

You can check the ASTAP solution by annotating with database stars. See attached. They all match

-45.19 degrees is equivalent to 360-45.19 = 314.81 degrees. That is close to 308 but not the same. The reason is that nova.astrometry.net default doesn't uses the center pixel as reference. You can force it in the nova.astrometry.net advanced options ( CRPIX in center).

Then you get the angle 314.8 degrees E of N
https://nova.astrometry.net/user_images/10955955#annotated

The PI program has a bug in their FITS read/writer. I informed them but they are not willing to fix it. They even dispute it's existence which baffles me. See:
https://pixinsight.com/forum/index.php?threads/astrometric-solution-is-written-flipped-to-fits-and-xisf-file.20438/

If you flip the image in ASTAP (tools, rotate image, flip vertical, then save it) it will likely work in PI

Han

[han.k]

If you flip the image in ASTAP (tools, rotate image, flip vertical, then save it) it will likely work in PI

Han