[AstroPy] pywcs issue
Fri Mar 25 12:03:24 CDT 2011
> The WCS is not guaranteed to be defined outside of the image.
> Particularly with SIN projections, it is often the case that the results
> are invalid when outside of the image. wcslib (and pywcs) does not do
> any sanity checks for this.
Thank you for this clarification. One expects that the conversions will
become progressively more inaccurate as one moves further out from the
image. But it is strange that at the greatest possible distance away on
the sphere (~180 degrees away), results are similar to what one sees at
very small distances from the image center. I will check the SIN
projection equations to get a feel for this; I have not seen this happen
the more commonly used TAN projection.
We will, of course, use our own sanity checks to operationally overcome
Yogesh Wadadekar Tel: 91 20 25719238
National Centre for Radio Astrophysics e-mail: email@example.com
Post Bag 3, Ganeshkhind
Pune 411007, India
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