Version 8 (modified by etourigny, 3 years ago)

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Status of NetCDF CF-1.5 projection handling capability in work-in-progress NetCDF driver upgrade

This page was created to list/track progress as a supplement to work in October 2011 on wiki:NetCDF_Improvements, specifically wiki:NetCDF_exportUpdateChanges.

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. If and when we are able to test capability to import NetCDF variants that don't have a direct CF-1 equivalent, we should add a supplementary table.

ProjectionNameCF ExportCF ImportNetCDF JavaUpdatedNote
AEAAlbers Equal AreaYesYesYes18/10/11Tested regular 2SP version - see AEA note below.
AEAzimuthal equidistantYesYesNo18/10/11See (1) below
LAEALambert azimuthal equal areaYesYesYes18/10/11
LCC1SPLambert conformal???18/10/11Tested 2SP version - CF-1 claims to have a 1SP version, but params quite different to OGC WKT so not tested. See note below.
LCC2SPLambert conformalYesYesYes18/10/11LCC in GDAL/OGR
CEALambert Cylindrical Equal AreaYesPartialNo18/10/11Tested 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-1SPMercatorYesYesNo18/10/11See (1) below
M-2SPMercatorYesYesYes*18/10/11Parameters appear correct, loads in NetCDF Java and IDV, but appears translated slightly (a few arc-minutes) from expected position
OrthoOrthographicYesYesYes18/10/11
PSPolar stereographicYes*NoNo*18/10/11See projection comments below re parameters. File opens in IDV, but then
Rot PoleRotated poleNoNoNo18/10/11See projection comments below
StStereographicYesYesYes18/10/11
TMTransverse MercatorYesYesYes18/10/11

General notes:

(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.

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 imports an AEA with 2 identical std_parallels.
  • LCC : The OGC WKT 'Lambert_Conformal_Conic_2SP' maps clearly to LC 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 there a way to do this conversion?
  • 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 quite unusual, and significantly different from  http://www.remotesensing.org/geotiff/proj_list/polar_stereographic.html. In particular finding a CF-1 equivalent for 'latitude of natural origin' is proving difficult.
  • 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).

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