A question on keywords for 3-D images

[Arnold Rots]

I tend to agree with Tom McGlynn's first solution: make a binary table
with 32 rows.  One column will contain the 2-D arrays in its fields,
the other columns the variable parameters.

The geometry of the 2-D images can be specified through the iCTYPnnn,
etc., keywords.  I would suggest solving the BSCALE/BZERO problem by
storing the data as floats (E, not F) or doubles (D).

If the 2-D images are really big, and you need the parameters for
browsing, you may want to consider putting the image data into the
heap - that should be transparent to most FITS readers.

This format is similar to what we plan to use for the AXAF PSF files:
columns for parameters like energy and off-axis coordinates, and one
column with the data.  The data column contains vectors holding either
a 1-D radial PSFs or 2-D PSF images.  Depending on the size of those
vectors, they may be physically included in the body of the table or
located in the heap.

Hope this helps,

  - Arnold Rots

bob at ipac.caltech.edu wrote:
> Hello,
> 
> The SIRTF project is designing the format of its output products.  One
> of the products, for example, may contain 32-planes of 2-D data, all
> with the same geometry.  This would normally be a straightforward
> problem, just use a 3-D image, but there is a hitch ...
> 
> There is a set of at least 100 header keywords that have different
> values for each of the 2-D planes.
> 
> There are a number of workable solutions to this and we could just
> pick one and go with it.  However, a standard solution would be
> preferable since it would be better understood and it could be used
> directly in existing software.
> 
> 
> Here are two of the options being considered:
> 
>  1) Append plane number to keywords
> 
>    Use a 3-D image and append the plane number to the keyword names,
>    such as SIGMA01, SIGMA02, SIGMA03.  Is there any *STANDARD* way to
>    do this (especially one that existing software uses) ?  Also, each
>    plane may want to have its own BSCALE and BZERO. Is it possible to
>    specify these values for the individual planes?
> 
> 
>  2) Use FITS image extension
> 
>    Each extension would contain a 2D image and its own set of
>    keywords.  Going to this form loses the 3-D nature of the data with
>    each 2-D image looking like an independent image rather than being
>    part of a 3-D cube.  Also, there is a concern is that many FITS
>    readers and standard software may not be able to deal with files in
>    this form.  It may not be supported well in IRAF, CFITSIO, etc. for
>    3-D operations.
> 
> Thanks for any help,
>  Bob Narron

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Arnold H. Rots                                         AXAF Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 81                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head-cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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