Characterization question

[Douglas Tody]

As Tim J. also mentioned, we should not forget the existing FITS WCS
model which is relevant for parts of this, e.g. associating image axes
with world coordinate systems, or associating two image axes with a
spatial coordinate system.  In general we should distinguish between
higher level characterization of a dataset (Char), and actually defining
the precise WCS for the physical axes of the dataset.  Char for example
can characterize the spectral attributes of a dataset but it is a WCS
model which specifies which physical image axis is the logical spectral
axis, and the exact mapping to spectral coordinates.  There is a first
cut at this in the SIAV2 draft (which addresses cube data).  We retain
and use Characterization but also add a "Mapping" model which is based
directly on FITS WCS but which is defined as an abstract model
independent of serialization.

 	- Doug


On Sat, 12 Nov 2011, Laszlo Dobos wrote:

> Hi group,
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> How do I specify overlapping axes in characterisation?
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> Let's say I have a spectrum and want to give the spectral axis in both
> angstroms and velocities. Do I just add two axes and mark them both SPECTRAL
> and assume that they overlap?
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> What if I have an image with two spatial axes? Do I add two SPATIAL axes
> then or just one and assume that the resolution etc. is the same in both RA
> and Dec?
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> What if I have overlapping spatial axes, let's say ra,dec and (for a not too
> good example) also Mpc? How do I associate one Mpc axis with Ra and the
> other with Dec.
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> I'm sorry, if I misunderstood something about the whole thing. (Samples on
> the CDS server are unfortunately not available).
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> What I'm actually working on is a generic toolkit to characterize data cubes
> with any number of dimensions, and I want to allow using multiple scales
> along the axes.
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> Thanks,
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> -Laszlo
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>