Etienne, You should in theory just use OGRSpatialReference::IsSame() method to see if two coordinate systems are essentially equivelent, but it is not really all that perfect.
Best regards, On Fri, Oct 7, 2011 at 4:36 PM, Etienne Tourigny <etourigny....@gmail.com> wrote: > Hi all, > > I would appreciate any hints as to how I can compare 2 > WKT/OGRSpatialReference objects. > > My goal is to make sure that a more detailed WKT (with authority codes > and explicit datum) corresponds (numerically) to a simpler one, such > as in the following examples. > > I understand that the oSRSGDAL.exportToPrettyWkt() function can remove > AXIS, AUTHORITY and EXTENSION nodes, but how can I guarantee that the > PARAMETER nodes are in the same order? Does FixupOrdering() solve that > problem? > > Furthermore, How could I compare the datums? > > > > > CF=[PROJCS["unnamed", > GEOGCS["unknown", > DATUM["unknown", > SPHEROID["Spheroid",6378137,298.2572221010002]], > PRIMEM["Greenwich",0], > UNIT["degree",0.0174532925199433]], > PROJECTION["Lambert_Conformal_Conic_2SP"], > PARAMETER["standard_parallel_1",-18], > PARAMETER["standard_parallel_2",-36], > PARAMETER["latitude_of_origin",0], > PARAMETER["central_meridian",134], > PARAMETER["false_easting",0], > PARAMETER["false_northing",0]]] > > GDAL=[PROJCS["GDA94 / Geoscience Australia Lambert", > GEOGCS["GDA94", > DATUM["Geocentric_Datum_of_Australia_1994", > SPHEROID["GRS 1980",6378137,298.2572221010002, > AUTHORITY["EPSG","7019"]], > TOWGS84[0,0,0,0,0,0,0], > AUTHORITY["EPSG","6283"]], > PRIMEM["Greenwich",0], > UNIT["degree",0.0174532925199433], > AUTHORITY["EPSG","4283"]], > PROJECTION["Lambert_Conformal_Conic_2SP"], > PARAMETER["standard_parallel_1",-18], > PARAMETER["standard_parallel_2",-36], > PARAMETER["latitude_of_origin",0], > PARAMETER["central_meridian",134], > PARAMETER["false_easting",0], > PARAMETER["false_northing",0], > UNIT["metre",1, > AUTHORITY["EPSG","9001"]], > AUTHORITY["EPSG","3112"]]] > > > > Another option is exporting to PROJ.4 strings, but there are the > +towgs84 that shows up , plus some differences in +datum vs. +ellps. > > e.g. > > CF=[+proj=utm +zone=55 +ellps=WGS84 +units=m +no_defs ] > GDAL=[+proj=utm +zone=55 +datum=WGS84 +units=m +no_defs ] > or > CF=[+proj=lcc +lat_1=-18 +lat_2=-36 +lat_0=0 +lon_0=134 +x_0=0 +y_0=0 > +ellps=GRS80 +units=m +no_defs ] > GDAL=[+proj=lcc +lat_1=-18 +lat_2=-36 +lat_0=0 +lon_0=134 +x_0=0 > +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs ] > > > > many thanks, > Etienne > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev > -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmer...@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Software Developer _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
