Coordinate specification in Data Cubes (Was: Re: Complex data, Cube data

[Brian Thomas]

On Tuesday 16 May 2006 11:43 am, Doug Tody wrote:
> Hi Arnold -
> 
> On Mon, 15 May 2006, Arnold Rots wrote:
> > Several months ago I sent some examples of how STC elements would give
> > a proper metadata description of data cubes and how to ask for such a
> > cube using STC metadata.
> > Could that information be merged into what you are doing in this area?
> 
> Possibly.  The chief issues are that a data cube is a fairly constrained
> problem (N-D image matrix plus a WCS) which is already adequately by FITS
> WCS, and FITS and FITS WCS is what is already in use to store, transport,
> access, and analyze cube data.  Anything we use for cube coordinates has
> to either be based on FITS or at least have a clear mapping to FITS WCS to
> provide reasonable support for existing data and software.  The remaining
> issues of describing cube data can already be dealt with by the generic
> dataset metadata (Characterization etc.) being developed with SSA.

	There must be a different definition of 'data cube' in play here than I understand.
	An N-D image matrix would be one kind of data cube, but there are many others
	which are not image based at all.

	Now, as (I understand) a data cube may not have image data, then it is preferable to have a generalized 
	coordinate specification which is not tied to something which is necessarily an image, 
	(or FITS) such as  the STC provides. I agree that the STC must have a general mapping 
	back to the WCS, in the case that the cube has some (cutout) structure which is like an 
	image, but that doesn't mean we should WCS.

	We approached this problem about 2 years ago with the MatrixQuantity (+CompositeQuantity)
	= data cube, and found (at that time) a successfull resolution of how to embed/describe 
	the STC coordinates within datacubes.

	=brian