[COVERAGE] was: Re: [QUANTITY] Plea for pragmatism

[Doug Tody]

Pat - I am convinced by the discussion so far that my bandpass-oriented
strawman is not sufficient and we need to fold in something to describe the
"sampling" as you call it, and errors.  We should still end up with a fairly
simple and uniform set of summary data models for data characterization.
If this can be done soon enough we would like to use it (even an early
version) for data queries in SSA.    Doug


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 :-)