How do I determine the rotation of an image in the ASTAP desktop interface?

[Jeff Smith]

I use ASTAP with NINA to plate solve, and after a successful Plate Solve through ASTAP behind the scenes, NINA reports the rotation of the image. For my setup with the camera & OTA oriented the way I have it, it is reported as about 270 degrees in NINA.

This works when I plate solve the last image I took. But I'd like to obtain the rotation value from previous images, taken on previous days. So I launch ASTAP from the desktop, load a RAW file I took from a previous day, and hit the plate solve button in ASTAP. In the data returned, I'm not understanding where to find rotation. I see three fields that I think might pertain to rotation. They are:

CROTA1 = -9.245458534445E+001 / Image twist X axis (deg)
CROTA2 = -9.244078347877E+001 / Image twist Y axis (deg) E of N if not flipped.
OBJCTROT= 0.0 / [deg] planned rotation of imaged object

For that same image, when I took it and plate solved it in NINA the other day (with ASTAP as the plate solver), NINA reported the rotation as 270.

Do CROTA1 and CROTA2 refer to rotation? If so, how do I calculate it based on the values provided above? If not, how to I obtain degree-based rotation like NINA shows, using the ASTAP desktop interface and a previously taken image? Thank you!

[han.k]

Hi Jeff,

Best is to read crota2. It indicates -92.44 degrees east of north. The is equal to 360-92.44= 267.66 degrees west of north.

If you have an equatorial mount then after the equatorial flip your camera will rotate 180 degrees making it more complicated. I don;y know if Nina compensates for that.

ASTAP reports crota2. This is normally east of north unless the camera produces flipped images. If flipped then it will be west of north. So probably more confusing.

I wrote something here:
http://www.hnsky.org/astap#viewer_angle

If you have more questions please ask.

Han

[Jeff Smith]

Thanks so much Han, very helpful!