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Re: convert to pixel to RA and DEC in degrees? [message #49561 is a reply to message #49555]

Thu, 03 August 2006 07:12

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

adisn123@yahoo.com writes:
> Forgot one more thing.
>
> When applying "xyad" procedure to convert pixel coordinates to RA and
> DEC,
> the North direction of RA and DEC coords should align with the North
> direction of pixel coords?

It doesn't have to be aligned. It depends on how the telescope or
camera was pointed.

> If it is, then the image should be rotated in such a way that its North
> in RA and DEC should
> match with the North of pixel coords. I took a look at the image 's
> header to look for how many degrees I should rotate such that they
> align perfectly each other, but I can't find anything relevant to the
> rotation degrees.

Some FITS images have a CROTAn keyword. Others have a rotation
matrix, which is stored in CDn_n, I believe. More info can be found
here,
http://fits.gsfc.nasa.gov/fits_wcs.html

Craig

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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		Re: convert to pixel to RA and DEC in degrees? By: adisn123 on Thu, 03 August 2006 09:45
		Re: convert to pixel to RA and DEC in degrees? By: Craig Markwardt on Thu, 03 August 2006 07:12
		Re: convert to pixel to RA and DEC in degrees? By: Wayne Landsman on Wed, 02 August 2006 09:57
		Re: convert to pixel to RA and DEC in degrees? By: adisn123 on Wed, 02 August 2006 09:50

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