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Having worked with the importing WCS output via GeoTIFFs for use with NetCDF-Java i'm not sure it's possible to define a curvilinear model coordinates using the current GeoTIFF tag set. The pertinent portion of the GeoTIFF specification is here: http://www.remotesensing.org/geotiff/spec/geotiff2.6.html#2.6.1 There are two transformation types: 1) Define a tie point as x,y[,z] along with pixel x,y,[z] deltas. *or* 2) Define a transformation matrix such that m(x,y,z,1) = M_t * i(x,y,z,1) with M_t being a 4x4 transformation matrix and m being model coord and i being image coord. I've validated the GeoTIFF IOSP against all the sample GeoTIFFs available at the remotesensing.org site and have yet to see an implementation of type 2. I would take this to mean that even if one were to output a transformation of type 2 it would be unlikely that client software would support it (since there doesn't seem to exist validation data for it). That being said I don't think a type 2 definition could be used to define curvilinear mode coordinates. I guess the point is that WCS support for curvilinear grids would need an output format other than GeoTIFF. The only way to specify a curvilinear grid with GeoTIFF would be to provide model data as a regular grid with a (known) projection mapping to the curvilinear coordinates. I don't think this provides the desired flexibility (projections are limited to known ESG projection-algorithm/parameter-sets or projections via EPSG codes). NetCDF-CDF output from WCS would be needed. I apologize if i've stated the obvious... Tom On Jun 15, 2011, at 10:00 PM, john caron wrote: > some terms as far as i understand: > > regular grids: 1d x, y coordinates evenly spaced. only > ones WCS 1.0 allows > irregularly spaced grids: 1d x,y, but dont have to be even, eg gaussian > latitudes. > curvilinear grids: 2d x,y but each section is a quadilateral > and connected to its neighbor (implicit topology) > > CF allows both irregular and curvilinear grids. one could extend WCS to > return netcdf/CF irregular and curvilinear grids, without regridding. > > unstructured grids: arbitrary meshes, explicit topology, no CF standard yet. > > John, why do you want WCS? To get geotiffs, or ?? > > On 6/15/2011 7:25 PM, Ben Domenico wrote: >> >> Hi John et al., >> >> I am currently at the OGC Technical Committee meetings so your note is quite >> timely. My concept of how this sort of capability might be worked into the >> standards -- from the netCDF point of view anyway -- is via the CF >> conventions. We are currently working on a CF extension for the OGC >> netCDF core standard. At the same time we are working on a CF-netCDF >> encoding standard for WCS 2.0. But my understanding is that >> irregular/curvilinear grids are not formally adopted yet as part of the CF >> conventions. When these grids officially become part of CF, we can then do >> a revised extension to CF-netCDF and to WCS. >> >> Please correct me if I'm wrong about the status of irregular/curvilinear >> grids in CF. If you have suggestions for better ways to accomplish this, >> let me know. But for now this is the general outline of the plan for >> getting this into the formal standards world. >> >> For what it's worth. >> -- Ben >> >> On Wed, Jun 15, 2011 at 6:23 PM, John Maurer <jmaurer@xxxxxxxxxx> wrote: >> Thanks for the explanation, Ethan. If TDS could handle the regridding >> itself, then it could work. I assume this is what's happening on the backend >> via TDS/ncWMS for GetMap requests since the WMS spec doesn't handle >> irregular/curvilinear grids either (right?). I was hoping a future >> enhancement could someday do the same for TDS WCS. Something for the >> suggestion box. >> Cheers, >> John >> >> >> On Wed, Jun 15, 2011 at 2:17 PM, Ethan Davis <edavis@xxxxxxxxxxxxxxxx> wrote: >> Hi John, >> >> TDS currently only supports WCS 1.0.0. The WCS 1.0.0 specification >> itself does not support requesting or returning irregular/curvilinear >> grids. I believe the same is true for WCS 1.1.0. >> >> I don't belive this is necessarily the case for WCS 2.0. However, the >> 2.0 specification is written in the new core/extensions paradigm and I >> don't believe the extensions necessary to request or return >> irregular/curvilinear grids are yet written. >> >> The TDS WCS implementation does not currently support regridding data. >> So, currently one gets the data from the WCS in the same projection in >> which the data is stored. The combination means the TDS WCS can only >> serve regularly gridded data. >> >> Ethan >> >> On 6/15/2011 5:31 PM, John Maurer wrote: >> > Hi All, >> > We now use the WCS service through TDS to serve GeoTIFF files to users. >> > Since it only works for regular grids, I was wondering if TDS could be >> > enhanced in the future to support irregular/curvilinear grids via WCS? >> > TDS/ncWMS already handles curvilinear grids via WMS, so I was hoping the >> > same sort of intervening magic could be applied for TDS' WCS service? >> > Thoughts? >> > Thanks for listening!, >> > John Maurer >> > Pacific Islands Ocean Observing System (PacIOOS) >> > University of Hawaii at Manoa >> >> _______________________________________________ >> thredds mailing list >> thredds@xxxxxxxxxxxxxxxx >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/mailing_lists/ >> >> >> _______________________________________________ >> thredds mailing list >> thredds@xxxxxxxxxxxxxxxx >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/mailing_lists/ >> >> >> _______________________________________________ >> thredds mailing list >> thredds@xxxxxxxxxxxxxxxx >> For list information or to unsubscribe, visit: >> http://www.unidata.ucar.edu/mailing_lists/ > > _______________________________________________ > thredds mailing list > thredds@xxxxxxxxxxxxxxxx > For list information or to unsubscribe, visit: > http://www.unidata.ucar.edu/mailing_lists/
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