[AstroPy] Changing dimensionality of WCS

James Turner jturner at gemini.edu
Tue Sep 24 16:06:50 EDT 2013

I don't know the answer re. astropy.wcs but it would be good if
one could ultimately slice an nddata object and have the
dimensionality and WCS reduced automatically if applicable (a bit
like in IRAF but, hopefully, better) :-). It seems that an NDData
can already be sliced directly but "support for WCS and units is
not yet implemented". Maybe some more WCS manipulation routines
are needed first...



On 24/09/13 15:49, David Berry wrote:
> On 24 September 2013 19:23, Adam Ginsburg <adam.ginsburg at colorado.edu> wrote:
>> When working with data cubes, I often need to extract WCS information
>> for 1 or 2 of the WCS dimensions.   The docs
>> (http://docs.astropy.org/en/latest/wcs/index.html) give decent
>> examples of how to generate a WCS from scratch, but I don't see any
>> obvious way to extract a lower-dimensional WCS from a WCS.  Does such
>> functionality exist?  If not, does it make sense to generate a WCS
>> from scratch and copy over just the relevant parameters?
> This is an example of the general problem - given two arbitrary
> coordinate systems, one with N axes and one with M axes, is there a
> transformation between them, and if so, what is it? It is addressed in
> pyast by the "convert" method. If you need ideas for an API see
> http://starlink.jach.hawaii.edu/docs/sun211.htx/node245.html
> Implementing this sort of feature in a general way is tricky but can
> be done. For simpler cases where you just want to pick a specified
> subset or superset of axes from a coordinate system, pyast uses
> "pickaxes". See
> http://starlink.jach.hawaii.edu/docs/sun211.htx/node348.html
> I know pyast is not astropy, but I point these out in case ideas are
> need for how to approach these issues.
> David
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