| Re: convert to pixel to RA and DEC in degrees? [message #49555] |
Thu, 03 August 2006 09:45 |
adisn123
Messages: 44
Registered: July 2006
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Member |
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THank you all. It was a great help.
Craig Markwardt wrote:
> 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
>
> --
> ------------------------------------------------------------ --------------
> Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
> Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
> ------------------------------------------------------------ --------------
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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
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Senior Member |
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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
--
------------------------------------------------------------ --------------
Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
------------------------------------------------------------ --------------
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| Re: convert to pixel to RA and DEC in degrees? [message #49581 is a reply to message #49561] |
Wed, 02 August 2006 09:57 |
Wayne Landsman
Messages: 117
Registered: January 1997
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Senior Member |
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xyad.pro in the IDL Astronomy library does return the RA and Dec vectors as
double precision
IDL> xyad,h,23,23,aa,dd
IDL> help,aa,dd
AA DOUBLE = -0.0063888890
DD DOUBLE = 0.0063888890
Perhaps you are confused by the optional printing, which is to display to
tenths of a degree in declination
IDL> xyad,h,23,23
X Y RA DEC RA_2000 DEC_2000
23.00 23.00 -0.0064 0.0064 23 59 58.47 +00 00 23.0
The hr mn sc display format can be adjusted using the the PRECISION keyword
IDL> xyad,h,23,23,precis=4
X Y RA DEC RA_2000 DEC_2000
23.00 23.00 -0.0064 0.0064 23 59 58.46667 +00 00 23.0000
--Wayne
<adisn123@yahoo.com> wrote in message
news:1154536095.539610.137920@i3g2000cwc.googlegroups.com...
> Does anyone know a procedure which does converting job from pixel
> coordinates to RA and DEC in degrees using the image's fits header?
>
> I know there is xyad procedure in IDL library, but I want my result
> goes up to double precision.
>
> Is there any better one than xyad?
>
> Thanks.
>
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| Re: convert to pixel to RA and DEC in degrees? [message #49583 is a reply to message #49581] |
Wed, 02 August 2006 09:50 |
adisn123
Messages: 44
Registered: July 2006
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Member |
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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?
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.
adisn123@yahoo.com wrote:
> Does anyone know a procedure which does converting job from pixel
> coordinates to RA and DEC in degrees using the image's fits header?
>
> I know there is xyad procedure in IDL library, but I want my result
> goes up to double precision.
>
> Is there any better one than xyad?
>
> Thanks.
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