NetCDF <--> GML/JPEG2000

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Here is a conversation about NetCDF and GML/JPEG 2000. I have taken the liberty of posting it to both the galeon list, and the gmljp2 mailing list. I hope that we can make sure that the GML/JPEG2000 specification can accomodate the netCDF community. In particular, I would ask members of the GML/JPEG2000 list to comment on some of the questions raised below.
NOTE: I have edited a bit for readability. Thus far, Frank W's comments are 
prefixed by [FW:],John Caron's by [JC:], mine by [SPF:]

On 4/12/05, John Caron <caron@xxxxxxxxxxxxxxxx> wrote:
[JC:]    1.  scientific data is typically 4D, so the client  must know how to
handle a vertical and time dimension, as well as the usual 2D
horizontal. The vertical layers  and time series are the main
relationships we'd like to express with multiple "images".

[FW:] I think that the GML coverage description approach has very good
tools to describe addiitional dimensions, including unusual  dimensions
like pressure and geopotential height.  However, I think some
conventions on how this should be done still need to be prepared
to ensure respectible interoperability.



[JC:]    2. the vertical dimension is often not height, more  like pressure or
"geopotential height" that can be approximately mapped to height.


 [JC:]   3. We would generally prefer  to transfer the  floating point data
values as close as possible to what they are in the file,  and let the
client assign false color maps. It would be nice if the  scientific user
who is using a GIS package could access the underlying  data values. Is
that possible in JPEG2000?

[FW:] My understanding is that internally JPEG2000 data streams
are integers with potentially up to 31 bits of precision  (not exactly
sure about this part), so any floating point data would  inevitably need
to be scaled.



 [JC:]   4. The horizontal grid is not always evenly spaced in  scientific
data. I realize that resampling is an important service,  but  it would
also be useful to show the data in its native resolution. Is that
possible in JPEG2000?

[FW:] I don't think there is any standard approach to describing  this in GML
coverage descriptions.  Would you essentially transmit along
geolocation layers (lat and long) as is done with some NASA HDF
products?  A set of GCPs?



[JC:] I wonder if you have any thoughts on the  suitability/limitations of "GML
in JPEG2000" with respect to these issues? GML still  seems a bit green;
do you think its ready for full production use? Is the  OGC ready to add
JPEG2000 to its list of WCS formats?

[FW:] I would add that the description of user defined coordinate systems
(using standard projection methods like transverse mercator, but
custom parameters) has not yet really been addressed in the GML-in-
jpeg2000 IE though we hope to.  In that sense, the coordinate system
aspect of gmljp2 is still quite "green".

I would add that one approach is encoding your entire dataset in
JPEG2000 with a GML coverage description embedded.  Another
might be to use the "same" GML coverage description but embedding
it in a netCDF attribute, and come up with a specification for a URN
format to refer to specific variables and dimensions in the netCDF
file.



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