Hello, I'm doing some work on updating the GDAL NetCDF driver to be able to properly export to and import from CF-1 compliant files encoded with map projection (Grid Mapping) information (see http://trac.osgeo.org/gdal/ticket/2893 for background).
The driver as it stands doesn't export properly to NetCDF (eg from GeoTiff) for many projections: the issue is that GDAL stores projection information internally in OGC WKT form, and the driver has to 'map' these to appropriate CF-1 attributes when exporting - and several of these mappings aren't correct currently (eg Lambert Conformal Conic and Transverse Mercator were ok, but Albers Equal Area, Azimuthal Equidistant and others weren't working). The main issue seems to be that for many projections, where OGC WKT uses an attribute like 'latitude_of_center', the CF-1 closest corresponding attribute seems to be 'latitude_of_projection_origin'. For a projection such as Albers Equal Area, do these mean exactly the same thing? Testing the resultant translated file in IDV once I've added the above attribute mapping suggested the reprojected file is displaying with the correct coordinates. I'm not a geodsy or projections expert, but looking at the remotesensing.org and other pages suggested these parameters may be equivalent. Also with regard to longitude paramaters: it seems for some CF-1 projections such as Albers Equal Area, the 'longitude_of_center' attrib in WKT needs to map to 'longitude_of_central_meridian' in CF-1, whereas in others such as Lambert azimuthal equal area, 'longitude_of_center' needs to map to 'longitude_of_projection_origin'? (http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/apf.html) Would appreciate any comments, or even ways to improve testing strategy used. I'm aware of the CF-1 compliance checkers, and possibly should try the NetCDF Java API to check that points correspond. cheers, Patrick. _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
