| Shifted origin using Polywarp and Poly_2d [message #56749] |
Tue, 13 November 2007 14:42  |
jdshaw
Messages: 7
Registered: October 2007
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Junior Member |
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Hi,
I have some 2k x 2k astronomical images for which I need to correct
the astrometry. I've tried using POLYWARP and POLY_2D, but they dont
give good results as there is a reference pixel that should not be
moved. The reference pixel is near the middle of the image ( e.g.
[1079.51, 1007.41]) that corresponds to a particular celestial
coordinate.
I get much better agreement when I shift the origin to the reference
coordinate for my reference vectors as the distance from the reference
pixel is related to how much the coordinate shifts. I can get a good
set of matrices from Polywarp this way (much better than having the
origin at the corner of the image), but I am not sure how to get
POLY_2D to warp around a point that is not [0,0].
Any suggestions would be appreciated.
Thanks - John
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| Re: Shifted origin using Polywarp and Poly_2d [message #56831 is a reply to message #56749] |
Wed, 14 November 2007 06:42  |
wlandsman
Messages: 743
Registered: June 2000
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Senior Member |
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On Nov 13, 5:42 pm, jds...@udel.edu wrote:
> Hi,
>
> I have some 2k x 2k astronomical images for which I need to correct
> the astrometry. I've tried using POLYWARP and POLY_2D, but they dont
> give good results as there is a reference pixel that should not be
> moved. The reference pixel is near the middle of the image ( e.g.
> [1079.51, 1007.41]) that corresponds to a particular celestial
> coordinate.
I don't quite understand what you are doing -- what are you using to
correct the astroemtry? if the reference pixel is one of the grid
point in polywarp then it shouldn't be moving.
You might want to look at hastrom.pro ( http://idlastro.gsfc.nasa.gov/ftp/pro/astrom/hastrom.pro
) which might either already be doing what you need, or provide some
hints.
If instead, you have a list of star X,Y and celestial positions you
could try astromit.pro http://idlastro.gsfc.nasa.gov/ftp/contrib/landsman/mousse/as tromit.pro
- it also need astrom.pro) or you could use the very cool software at
http://astrometry.net. Note that once you have an astrometric
solution, you can set the reference pixel to anything you want.
--Wayne
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