|Version 15 (modified by pds, 20 months ago)|
Status of NetCDF CF-1.5 projection handling capability in work-in-progress NetCDF driver upgrade
The list of supported CF-1.5 projections is shown at http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/apf.html .
The table below shows tested ability to export projections from a GDAL raster - originally in GeoTIFF - to NetCDF CF-1.5 in each supported projection.
The shorthand projection names listed below correspond to their names in the source files and hopefully are fairly self-explanatory - they've been listed in the same order as that shown on the CF-1.5 appendix page.
Note: the current import capability has been tested to be the inverse of the export capability. We would appreciate any help in obtaining valid test files for each of these projections. If and when we are able to test capability to import NetCDF CF-1.5 variants that don't have a direct OGC WKT equivalent, we should add a supplementary table.
|Projection||Name||CF Export||CF Import||NetCDF Java||Updated||Note|
|AEA||Albers Equal Area||Yes||Yes||Yes||18/10/11||Tested regular 2SP version - see AEA note below.|
|AE||Azimuthal equidistant||Yes||Yes||No||18/10/11||See (1) below|
|LAEA||Lambert azimuthal equal area||Yes||Yes||Yes||18/10/11|
|LCC1SP||Lambert conformal||?||?||?||18/10/11||See note below.|
|CEA||Lambert Cylindrical Equal Area||Yes||Partial||No||18/10/11||Tested regular OGC WKT with std_parallel version (CF-1 has alternative scale_factor_at_projection_origin version, see notes below). See (1) below re NetCDF-Java loading.|
|M-1SP||Mercator||Yes||Yes||No||18/10/11||See (1) below|
|M-2SP||Mercator||Yes||Yes||Yes*||18/10/11||Parameters appear correct, loads in NetCDF Java and IDV, but appears translated slightly (a few arc-minutes) from expected position|
|PS||Polar stereographic||Yes*||Yes||No*||18/10/11||Believe we can translate parameters correctly, but see comments below. Translated file opens in NetCDF-Java IDV, but doesn't display as correctly georeferenced.|
|Rot Pole||Rotated pole||No||No||No||18/10/11||See projection comments below|
(1) For projections that won't load correctly as referenced grids in NetCDF Java, we've contacted the developers to ask for clarification/testing support. In most cases, the CF-1 attributes seem appropriate.
- Update 20/10/2011: One of the NetCDF lead developers has acknowledged NetCDF Java hasn't handled these projections previously, and is going to upgrade: see http://www.unidata.ucar.edu/mailing_lists/archives/netcdf-java/2011/msg00159.html
Issues with CF-1 implementation of specific projections:
- AEA : The OGC WKT version has 2 Std parallels - whereas the CF-1.5 version says it can have either 1 or 2 std parallels. How should the CF 1SP version be converted to OGC WKT, and vice-versa?
- Currently the driver, on import and finding an AEA with only 1 std parallel, will set the 2nd std parallel in the WKT as identical to the first.
- LCC : 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'. Is mapping std_parallel_1 maps to latitude_of_origin and setting scale_factor=1 correct? (see bug #3324)
- CEA : 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 back from OGC WKT?
- PS : 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'. 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.
- Rot pole : Not able yet to test: as seems GDAL needs support of advanced proj4 strings that can handle rotated coord systems (see bug #4285).
(18.7 KB) - added by pds
20 months ago.
NetCDF version of original UTM-encoded small LANDSAT subset raster
(59.1 KB) - added by pds
20 months ago.
Tarball containing input exported to NetCDF in different projections
(43.2 KB) - added by etourigny
17 months ago.
horizontal datum parameters for use as reference for CF-1.7
- ellipsoid.csv (13.5 KB) - added by etourigny 17 months ago.
- prime_meridian.csv (1.6 KB) - added by etourigny 17 months ago.