Reported RA/Dec of target changes with image rotation

[ghawkins]

I believe I've found a problem with image rotation in AIJ.  I've been looking at AAVSO standard star fields and could not get the J2000 coordinates given by the AAVSO finder chart for comp stars to agree with those reported by AIJ (after platesolving) for the image I'd captured.  After considerable playing around, it appears the difference was being caused because I rotated the image in AIJ using Process, Rotate data 90 .......

Here's a example of what I've found.  Going back to the original science image for SA32 I captured, after platesolving with astronomy.net, the RA/Dec for a 9.3 mag comp star is reported by AIJ to be 12:56:03 14:15:27.  These are the correct coordintes.  However, if I rotate the AIJ image clockwise 90 degrees, AIJ now reports the RA/Dec coordinates of this star as 12:56:06 44:10:26. A further 90 clockwise and I get 12:56:34 44:11:06, another 90 degrees clockwise 12:56:31 44:16:07. The initial coordinates are reported with a further 90 degree rotation.

I can supply the image if required, or screenshots of what's happening.

[karenacollins]

The rotate image capability is a feature of the underlying ImageJ software. It is unfortunately not WCS header aware and will not adjust the RA and Decs after a rotate. You would need to plate-solve the image again after rotation, if you want to replace the WCS header information with corrected WCS information. We realize that can be a time-consuming effort for large image stacks, so hopefully someday we will have time to make the rotate feature WCS header aware.

In case you are not aware, if you just want to invert the image display in the X and/or Y axes, but not actually change the underlying image, use the Image_Menus > View > Invert options. Using these options, the displayed image will flip accordingly, and RA and Dec will display properly in any resulting image orientation.

Karen

[ghawkins]

Hi Karen,

Thanks for that explanation.  Now, I know if not a problem just an operational limitation, I can make this work.

Gary