Hi all, I am opening a seperate thread at this deals merely with the problems encountered in translating projection parameters to/from OGC WKT and CF-1.5.
I would appreciate any guidance in resolving these issues. In summary: 1) LCC (Lambert conformal): should include a scale_factor parameter in the 1 standard parallel case 2) CEA (Lambert Cylindrical Equal Area): how to convert the 'scale_factor_at_projection_origin' alternative to standard parallel to OGC WKT? 3) PS (Polar stereographic):This projection's parameters in CF-1 are significantly different from OGC/PROJ.4 , CF-1 standard parameters 'Either standard_parallel or scale_factor_at_projection_origin' is incompatible with OGC WKT, which requires both More detailed information (reproduced here) can be found at http://trac.osgeo.org/gdal/wiki/NetCDF_ProjectionTestingStatus 1) LCC 1SP (Lambert conformal) The OGC WKT 'Lambert_Conformal_Conic_2SP' maps clearly to LCC in CF-1 with 2 std parallels. The CF-1 spec claims that a 1SP version can be used, but it doesn't include a 'scale_factor' as does the OGC WKT 'Lambert_Conformal_Conic_1SP'. For import: Given discussion and example on #3324, and also support from NARCCAP project: it seems the CF-1 LCC 1SP projection is a 'degenerate' LCC-2SP with both SP's at the same location. Thus seems we can read with both 'std_parallel' (1 value) and 'latitude_of_projection_origin' mapping to latitude_of_origin (WKT) and setting scale_factor=1? This is the code's current behaviour (though perhaps could do more error-checking). For export: given the LCC-1SP can specifically include a scale_factor to control the projection (see http://www.remotesensing.org/geotiff/proj_list/lambert_conic_conformal_1sp.html), it seems this can't be directly exported to NetCDF without throwing away the scale factor. Perhaps the reasonable thing for now is to export the scale_factor to NetCDF, so it can at least be read back in. Otherwise, we'd have to try to translate the LCC-1SP to a LCC-2SP on the fly. 2) CEA (Lambert Cylindrical Equal Area): The CF-1 conventions claim this can be encoded with a 'scale_factor_at_projection_origin' alternative to standard parallel - how would this conversion be done from/to OGC WKT (which requires central_meridian and standard_parallel_1)? 3) PS (Polar stereographic) This projection's parameters in CF-1 are significantly different from http://www.remotesensing.org/geotiff/proj_list/polar_stereographic.html. In particular the CF-1 equivalent for 'latitude of natural origin' seems to be 'standard_parallel'. CF-1 defines either standard_parallel or scale_factor_at_projection_origin, which is incompatible with OGC WKT (and OGR) that requires both. Note: we have verified the current approach we take to mapping is the same used by at least one other NetCDF CF-1 user in the UCAR NARCCAP project. Current implementation (as of Dec. 13) uses the following rules: - WKT scale_factor maps to CF scale_factor_at_projection_origin - WKT central_meridian maps to CF straight_vertical_longitude_from_pole - WKT latitude_of_origin maps to WKT standard_parallel - WKT to CF: if WKT latitude_of_origin is positive then CF latitude_of_projection_origin is +90, else it is -90 (North vs. South Pole) - CF to WKT: unsupported if standard_parallel is not defined, as OGRSpatialReference::SetPS() requires both CF scale_factor_at_projection_origin Thanks Etienne _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
