| Re: change pixel scale [message #80321] |
Mon, 28 May 2012 09:17  |
spasoklampanas
Messages: 8
Registered: May 2012
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Junior Member |
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On May 27, 6:03 pm, Russell Ryan <rr...@stsci.edu> wrote:
> On May 26, 7:46 am, spasoklampa...@yahoo.com wrote:
>
>> Hi
>
>> I have some fits files (astronomy images) that have a different
>> pixel scale. How is it possible to bring them on the same pixel scale?
>> The given routine of degrade is not suitable, since it degrades the
>> image resolution by a factor of two, which is not my case.
>
>> Thanks a lot.
>
> So...
>
> There are several ways to skin this cat, and they depend on how
> careful you want to be. Before we get into those ways, you need to
> answer a few things about your images...
>
> (1) Do they both have WCS in the headers that you trust?
> (2) Are they astrometrically aligned already, and you just want to re-
> pixelate?
>
> If the answer to (1) is "no," then we need to fix that first.
> Hopefully, you know *roughly* where your field is and can just grab a
> bunch of stars either from the DSS or SDSS to get the precise WCS
> mapped out. If not, then you need to go outside of IDL get the job
> done.
>
> Then you can use hastrom.pro (in the IDL astro library) to register
> the two images. This does only a bilinear (I think?) interpolation
> --- which may not be good enough for you. If you have a weight map
> (or error image), then you need to process that as well --- but
> remember you'll need to work with variances!!
>
> If you don't like bilinear, then the only way I know how to do this is
> to go outside of IDL and use SCAMP and SWarp to get the job done.
>
> Good luck!
> Russell
Just to sound even more stupid now I got this error message:
% HASTROM: ERROR - No overlap found between original and reference
images
% HASTROM: Be sure you have the right headers and the right equinoxes
% Compiled module: WRITEFITS.
The Galactic coordinates of the cloud are the same. On ds9 I put
the cursor at the centre of the cloud and on both cases the galactic
latitude and longitude are the same. What is my mistake though?
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