Multi-dimensional Data Access minimal requirements

[Douglas Tody]

On Fri, 7 Mar 2014, Patrick Dowler wrote:

> "circle' is not a typo. The user would specify a circular region of interest 
> and the service would return a rectangular array that includes that circle. 
> The use of a circle avoids anyone assuming that any rotation would be 
> applied. If the client specifies range of coordinates or a polygon, we would 
> have to be more clear in documentation exactly how those were supposed to be 
> treated as they do carry orientation information. Basically, circle has no 
> orientation so it never implies anything and is the simplest 
> region-of-interest to deal with.

The basic concept of a cutout is that we "cutout" (without recomputing)
a region in multi-dim space, defined by the range of coordinates in each
dimension.  For the spatial limits of an image cutout the generalized
cutout region is a rectangle; restricting this to a square box enclosing
a circular region is unnecessarily restrictive without simplifying
anything.  If we want to forbid rotation that is easily done by
specifying the bounds of the cutout region on the two spatial axes.  The
fundamental restriction is that pixels/voxels are not recomputed but are
merely "cut out".

> For cutouts, the parameters I have are essentially the same as the WD-SIA-2.0 
> basic query parameters (POS, BAND, TIME, POL): they specify a region of 
> interest. The difference is that one capability (and REQUEST value) specifies 
> searching for data and the other cutout from a single selected dataset.

Good; the simple solution for both a discovery query and accessData is
to have the same ROI/FILTER parameters be the same in both cases (POS,
[SIZE explicit or folded into POS], BAND, TIME, POL).  The only thing
missing is then the capability to automatically "discover" virtual
images (cutouts or mosaics) in the discovery query.  This is quite
important for example, when querying against a wide field survey where
we have full coverage, and don't care at all about the individual images
composing the survey region.

 	- Doug