| Re: WCS Coordinates not kept with WRITEFITS [message #68979] |
Thu, 10 December 2009 07:30  |
Bringfried Stecklum
Messages: 75
Registered: January 1996
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Member |
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Laurence wrote:
> Hi,
> I am writing because I have a problem while creating new fits files
> and I could not find any similar topic on the web.
> Basically, I simply cut a small region from a larger fit file and save
> it with writefits .
>
> im1=readfits('pp.fit',hdr)
> temp1='p.fit'
> imnew1=fltarr(2000,2000)
> imnew1=im1(3303:3512,3095:3293)
> writefits,temp1,imnew1,hdr
>
> But in the newly created .fit file, the coordinates are off and then
> wrong !
> Is there a way to solve this ? (I have idl_6.0 )
>
> Thanks,
Of course, since the header needs to be updated as well to account for the size
and WCS change. The routine hextract from the IDL Astro Lib does the job of
extracting FITS subimages, see
http://idlastro.gsfc.nasa.gov/ftp/pro/astrom/hextract.pro
Regards,
Bringfried
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| Re: WCS Coordinates not kept with WRITEFITS [message #68980 is a reply to message #68979] |
Thu, 10 December 2009 07:30  |
jeanh
Messages: 79
Registered: November 2009
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Member |
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Laurence wrote:
> Hi,
> I am writing because I have a problem while creating new fits files
> and I could not find any similar topic on the web.
> Basically, I simply cut a small region from a larger fit file and save
> it with writefits .
>
> im1=readfits('pp.fit',hdr)
> temp1='p.fit'
> imnew1=fltarr(2000,2000)
> imnew1=im1(3303:3512,3095:3293)
> writefits,temp1,imnew1,hdr
>
> But in the newly created .fit file, the coordinates are off and then
> wrong !
> Is there a way to solve this ? (I have idl_6.0 )
>
> Thanks,
Hi,
you are saving the header of your big file along with the data of your
small file... it can not work. You would have to update the header
information (sorry, I don't use fits files so I can't help you on this
one). Mainly, the new coordinate of your top left (could be another
corner) corner is needed, as the resolution and map info should be the
same.
Jean
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| Re: WCS Coordinates not kept with WRITEFITS [message #69060 is a reply to message #68979] |
Tue, 15 December 2009 11:02 |
Laurence
Messages: 2
Registered: December 2009
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Junior Member |
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On Dec 10, 3:30 pm, Bringfried Stecklum <steck...@tls-tautenburg.de>
wrote:
> Laurencewrote:
>> Hi,
>> I am writing because I have a problem while creating new fits files
>> and I could not find any similar topic on the web.
>> Basically, I simply cut a small region from a larger fit file and save
>> it with writefits .
>
>> im1=readfits('pp.fit',hdr)
>> temp1='p.fit'
>> imnew1=fltarr(2000,2000)
>> imnew1=im1(3303:3512,3095:3293)
>> writefits,temp1,imnew1,hdr
>
>> But in the newly created .fit file, the coordinates are off and then
>> wrong !
>> Is there a way to solve this ? (I have idl_6.0 )
>
>> Thanks,
>
> Of course, since the header needs to be updated as well to account for the size
> and WCS change. The routine hextract from the IDL Astro Lib does the job of
> extracting FITS subimages, see
>
> http://idlastro.gsfc.nasa.gov/ftp/pro/astrom/hextract.pro
>
> Regards,
>
> Bringfried
Thanks! In the meanwhile I used IRAF which works very well .
Laurence
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