How to simply get all RA and Dec for detected sources, and position info (rotational angle, central RA Dec, etc.) from the header

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Jerry Zhang

Jul 21, 2022, 10:36:53 AMJul 21
to astrometry
Hello experts in,

After the solve-field I get plenty of the detected star in the .axy file with only X and Y pixel values in the image. Now I would like to transform them into their RA and Dec, but I need the position info like the orientation, scale, reference point position and pixels.

I can find reference point pixels and position in the headers of fits file, and CD matrix but I would like to directly get the central RA Dec and field rotation angle because my images are fixed FoV. 

These info are shown in the dialogue window:
Field center: (RA,Dec) = (60.821513, 35.265565) deg.

Field center: (RA H:M:S, Dec D:M:S) = (04:03:17.163, +35:15:56.035).

Field size: 7.28873 x 7.28477 arcminutes

Field rotation angle: up is -98.8361 degrees E of N

Field parity: neg

but where are they hiding in the final files? Or is there any way to simply get all the RA Dec for detected sources in .axy file?



Dustin Lang

Jul 21, 2022, 10:47:45 AMJul 21
to Jerry Zhang, astrometry

After you run solve-field, you can use the wcs-xy2rd program to convert from X,Y to RA,Dec:
    wcs-xy2rd -w image.wcs -i image.axy -o image.radec

To get additional information about a WCS solution, you can use:
    wcsinfo image.wcs
which will print out a bunch of stuff including ra_center, dec_center, orientation, etc.

Alternatively, if you set --crpix-center, then in the image.wcs file, the CRPIX1,CRPIX2 values will be the x,y pixel center of the image, and CRVAL1,CRVAL2 will be the central RA,Dec.


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Jerry Zhang

Jul 25, 2022, 1:09:08 PMJul 25
to astrometry
It works quite nice!
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