[ImageDM] Mapping

[CresitelloDittmar, Mark]

Doug,

I was looking at the model from the opposite side today.  Asking "what is a
ND-Cube or ND-Image", ignoring all the Obs/Char metadata stuff, and then
re-visiting ImageDM..

A couple quick questions.

1) pg 29:  "If multiple WCS instances are required for an image, this can
be expressed by merely having multiple instances of
Mapping,"
   The diagram (Figure 2 on pg 12) shows a 0..1 relation between Data and
Mapping.  was this supposed to be 0..*?

2) Is it possible to scale the data values?

3) Can you give an example of the content for "Mapping.AxisMap"?
    Say I have an image with WCS ("RA", "DEC", "Time"), pixel axes (#1, #2,
#3) plus value
    The 'Linear' portion is applied (CD matrix) to (#1, #2, #3) producing
intermediate axes.
    a) do these have names?

    AxisMap (pg 29) "is used to map the axes of the intermediate world
coordinates (i.e., after the CD or PC transform, which may transpose or
rotate the image axes) to the axes of
the final world coordinate system.

    This has to show that the result from Linear transform on  #1 and #2
(assuming no trasposition), go to the 2D SpatialAxis projection, while the
result of the #3 goes to TimeAxis.


And a couple comments below..


On Tue, Nov 19, 2013 at 4:00 PM, Douglas Tody <dtody at nrao.edu> wrote:

> In the current ImageDM, CoordSys is mainly used to define the coordinate
> systems used globally for metadata describing the overall image dataset
> (Image, Observation, Char, etc.).
>

So, this defines a singular coordinate system which is to be used
throughout the metadata portions of the model?
pg 12: "Image also adds a CoordSys element defining a uniform set of
(default) coordinate frames and units for all Image metadata including
Observation and Characterisation."

If my Data has WCS for the Spectral axis in both Wavelength and Energy,
(presumably via different Mapping-s), I CANNOT characterize my image in
both?



> It is highly desirable (from the client application perspective at
> least) to have a single set of coordinate frames used uniformly for all
> this higher level metadata.  It is pretty much required to do this in a
> use case such as a data discovery query response, where there are many
> table rows each describing a different dataset.  Otherwise we would have
> to add table columns to describe the frames used separately for each
> dataset/row, and the client would have a much harder time sorting out
> the information that comes back.
>

I can see that particular applications (like data discovery) may wish to
require a homogenized metadata set to simplify their use-case, but I'm not
sure that is a limitation on the generic model, but rather a requirement of
the application (SIAP).

 Mark
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