[PROJ] Proposal for a geodetic deformation model format

[Martin Desruisseaux]

Hello Chris

Thanks for the proposal, I had a quick look on it. The explanation about 
rational, required metadata, etc. are very nice. My first question would 
be who is the intended audience. Is it a proposal for the PROJ/GDAL 
community, or e.g. a starting point for standardization at OGC? The 
reason why I ask is because in my understanding, the choice of GeoTIFF 
format for PROJ/GDAL is based on pragmatic reasons specific to that 
community (close connection between GDAL and GeoTIFF since they are 
maintained by the same peoples; more familiarity with GeoTIFF than with 
HDF5 and CF-Conventions). They are valid reasons for PROJ/GDAL, but if 
the target audience is wider then I would suggest to reconsider since, 
if it was not for PROJ/GDAL convenience, I think HDF5 + CF-Conventions 
(i.e. NetCDF 4) would be more appropriate for those kind of data.

However a "GeoTIFF versus HDF5" discussion could be left for a separated 
thread. The vast majority of the proposal document would still apply in 
both formats, except the discussion about single versus multiple files 
which would not be needed anymore. Some attributes like "extent_east", 
"extent_north" would be revisited in a HDF5 format because they overlap 
(but are not identical) with standard CF-Conventions attributes, but the 
ideas would still the same.

     Regards,

         Martin