STC2 Design

[CresitelloDittmar, Mark]

​
Arnold,

There is an object in the STC2 prototype contained in the DatasetMetadata
model which is not included in the STC2 model that I'd like to bring up for
discussion.

The object is the "Mapping" object in section 6.11.  In the prototype, it
is a collection of FTransform objects in a composition relation.
Basically, this object owns and maintains the set of Transforms associated
with the DataProduct.  The Mapping object hangs directly
off of DataProduct along side the CoordSys (see Section 3 of Cube model).
The PixelFrame then, holds a reference to the appropriate Transform in
Mapping (Section 6.8 of DatasetMetadata model).

One benefit of this object, is that it encapsulates all of the transform
information (WCS) into one container, which is then easily accessible by
the DAL protocols.

In the posted STC2 model diagrams, the connections are somewhat different.
  + there is no Mapping container ( has never been part of your model )
  + the PixelFrameTransforms are owned (composition relation) by the
PixelFrame, so they are tightly bound.
  + the FrameTransform ( for mapping between non-pixel coordinate frames)
has no containing object.

I think there are 3 concerns here:
  1) It is unclear to me where the FrameTransform objects would reside if
one were to use them.. in a data product (Image)
  2) It seems to me that there may be use cases where a data product would
contain multiple images of the same shape
      which share coordinate systems  ( source and bkg images maybe ?).  In
such a case, one would want the pixel frames
      of each image to share the same transform definitions.  I admit, this
hasn't been thought through, but the current
      design doesn't permit the sharing of a PixelFrameTransform.
  3) For the DAL use case, to get a container describing the wcs
descriptions for the dataset, one would have to scan
      the PixelCoordSystem->PixelFrame-s to fine the PixelFrame Transforms,
and then the ?? objects to get the FrameTransforms
      and create an object with references to those.


I Hope this makes sense.
Mark
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