Thursday, August 28, 2014

Fixing a Map Projection Issue for the SNAP S1TBX Toolbox

[This post was written for the Nest SAR Toolbox, which is now replaced by the SNAP SAR Toolbox]

In the SNAP Sar Toolbox you have a choice of coordinate systems:

For some of these, however, SNAP reports the error "Axis Too Complex".

I compared a map projection that works with one where “Axis too complex” error is reported. Map projections that work contain these lines:
 
  AXIS["Easting", EAST], 
  AXIS["Northing", NORTH]

While the non-working ones contain these lines, which apparently are wrong or unprocessable by SNAP
  AXIS["Easting", "North along 90 deg East"], 
  AXIS["Northing", "North along 0 deg"],



If you use the graph builder or command line (gpt) where the parametres are defined in an XML-file, you can manually replace these lines in the graph file (xml file) for the projection definition, then it works! An example for such an XML-file used by SNAP is here.

Another example, this one works

 PROJCS["WGS 84 / Australian Antarctic Lambert", 
  GEOGCS["WGS 84", 
    DATUM["World Geodetic System 1984", 
      SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]], 
      AUTHORITY["EPSG","6326"]], 
    PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]], 
    UNIT["degree", 0.017453292519943295], 
    AXIS["Geodetic longitude", EAST], 
    AXIS["Geodetic latitude", NORTH], 
    AUTHORITY["EPSG","4326"]], 
  PROJECTION["Lambert_Conformal_Conic_2SP", AUTHORITY["EPSG","9802"]], 
  PARAMETER["central_meridian", 70.0], 
  PARAMETER["latitude_of_origin", -50.0], 
  PARAMETER["standard_parallel_1", -68.5], 
  PARAMETER["false_easting", 6000000.0], 
  PARAMETER["false_northing", 6000000.0], 
  PARAMETER["scale_factor", 1.0], 
  PARAMETER["standard_parallel_2", -74.5], 
  UNIT["m", 1.0], 
  AXIS["Easting", EAST], 
  AXIS["Northing", NORTH], 
  AUTHORITY["EPSG","3033"]]


EPSG3031 works not: 
  PROJCS["WGS 84 / Antarctic Polar Stereographic", 
  GEOGCS["WGS 84", 
    DATUM["World Geodetic System 1984", 
      SPHEROID["WGS 84", 6378137.0, 298.257223563, AUTHORITY["EPSG","7030"]], 
      AUTHORITY["EPSG","6326"]], 
    PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]], 
    UNIT["degree", 0.017453292519943295], 
    AXIS["Geodetic longitude", EAST], 
    AXIS["Geodetic latitude", NORTH], 
    AUTHORITY["EPSG","4326"]], 
  PROJECTION["Polar Stereographic (variant B)", AUTHORITY["EPSG","9829"]], 
  PARAMETER["central_meridian", 0.0], 
  PARAMETER["Standard_Parallel_1", -71.0], 
  PARAMETER["false_easting", 0.0], 
  PARAMETER["false_northing", 0.0], 
  UNIT["m", 1.0], 
  AXIS["Easting", "North along 90 deg East"], 
  AXIS["Northing", "North along 0 deg"], 
  AUTHORITY["EPSG","3031"]]

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