[COVERAGE]

[Arnold Rots]

Coverage is fully taken care of the in the Space-Time Coordinate
metadata, and it covers spatial, temporal, spectral, and redshift
coordinates - in a uniform way.

  - Arnold

David Berry wrote:
> 
> Pat,
>     I must not have expressed myself clearly - I am all in favour of
> having uniform models for things like COVERAGE. My suggestion was that
> each domain (i.e. a subset of the axes, 2 for spatial, 1 for
> spectral/temporal) could be described uniformly using components
> representing sensitivity, resolution, sample size, and error. This seems
> pretty similar to the CVO model you described - your "bounds" is my
> "sensitivity", and I've not explicitly sectioned off the other items into
> a separate "sampling" structure. The only substantive difference that I
> can see is that I've got "error" and you have got "fill factor". I've
> not problems with fill factor being added to the list.
> 
> David
> 
> 
> 
> ----------------------------------------------------------------------
> Dr David S. Berry    (dsb at ast.man.ac.uk)
> 
> STARLINK project                        Centre for Astrophysics
> (http://www.starlink.ac.uk/)            University of Central Lancashire
> Rutherford Appleton Laboratory          PRESTON
> DIDCOT                                  United Kingdom
> United Kingdom                          PR1 2HE
> OX11 0QX
> 
> 
> 
> On Fri, 31 Oct 2003, Patrick Dowler wrote:
> >
> > Coverage, or "bounds" as we call it in CVO, is a 1st order summary of the
> > full blown description. However, the model here doesn't make sense to me
> > because it does treat things uniformly when they are uniform and treat
> > them differently when they are different.
> >
> > The WCS is typically ~2d, so the spatial coverage/bounds has to be a 2d
> > construct. CVO uses polygons, but other  shapes would be fine depending on how
> > exact one wants to be... the idea is that you want to tell the difference
> > between "in" and "out" and whether two things overlap/intersect.
> >
> > Spectral and temporal axes are 1d, and a 1-d bound is an interval (loValue and
> > hiValue below). They are not error values on the refValue. What is "time of
> > observation"? The  observation starts at loValue and ends at hiValue, no??
> >
> > In the CVO model, each axis (spatial, spectral, temporal) has a  "bounds"
> > object and a "sampling" object. The bounds are polygon or interval
> > (currently). The sampling object has several parts: number of bins, bin size,
> > resolution, and fill factor. One can compute the Nyquist ratio from bin size
> > and resolution, which is what Alberto was referring to about data being
> > undersampled). So, all axes have the same sampling description and the bounds
> > description dpeends on the dimensionality. If you split up the two spatial
> > axes in an attempt to have 4 x 1d axes, you could use intervals for bounds
> > everywhere, but then you are essentially putting an axis-aligned bounding box
> > around the polygon, which is a worse characterisation of the WCS, for no good
> > reason.
> >
> > My thoughts, based on our experience actually trying to model this in general,
> > put it all into a database, actually describe different types of data this
> > way (WFPC2 images, 2QZ spectra, ROSAT fields, CFHT 12K images, etc)
> > and then query it in a uniform and general fashion.  Yeah, there are things
> > I'd do differently, but not much differently :-)
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              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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