[AstroPy] Pywcs: Creation, access to properties
astropy at liska.ath.cx
Fri Apr 29 11:04:26 EDT 2011
I have two questions about pywcs:
First is, how do I create a pywcs.WCS object not from a file, but with
certain parameters? The way I do it now is first to create a header with
the required keywords, and then use the pywcs.WCS constructor, but this
seems to me a bit indirect.
The second question is on how do I access some parameters in a robust
way? For example, I want to get the instrument resolution in arcsec out
of the image. Currently, I implemented it like
def get_resolution(wcs, units = None)
c = numpy.sqrt(numpy.sum((wcs.wcs.cd if wcs.wcs.has_cd()
else wcs.wcs.pc) ** 2, axis = 0))
if units is None:
if to_unit is not None else cc
for from_unit, to_unit, cc in zip(wcs.wcs.cunit, units, c)
but this looks a bit weird, and I feel that I still did not took all
possible cases to construct the WCS. Is there a simpler way?
This question arises since I often have to implement something like
"give me the pixel position just 1 arcsec upwards (in CCD orientation)
from the image center".
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