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

[William Pence]

Doug Tody wrote:
> Hi Brian -
> 
> On Tue, 16 May 2006, Brian Thomas wrote:
> 
>> 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.
> 
> It is certainly true that there are other kinds of 3-D data than uniformly
> sampled (pixelated) data cubes (or N-D versions of such cubes), however
> for the SIA upgrade this is the case we are specifically referring to.
> Radio data cubes for example are of this type, and they are generally
> stored in FITS format, with a FITS WCS, and the applications used to
> analyze and visualize these cubes are also FITS-based.  IFU data cubes in
> the Euro3D format are also FITS-based although the actual format is a FITS
> binary table and they are not simple FITS images.  A more careful look
> at Euro3D format is needed to determine what is required to support it.
> These are the two most widely-used cases I know of for fully sampled 3-D
> astronomy data; does anyone know of any others?  (Event data maybe, but
> it probably does not qualify as the energy/spectral measurement precision
> is generally very limited).

This may have been true in the past, but the technology is evolving rapidly. 
Newer types of photon counting X-ray detectors, such as micro-calorimeters, 
can measure the photon energy with relatively high precision.

Bill
-- 
____________________________________________________________________
Dr. William Pence                       pence at milkyway.gsfc.nasa.gov
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