OGR only supports the "+a=xxxxx +b=yyyyy" and "+a=xxxx +rf=zzzzz" combinations. It could be extended to support more combinations, but those 2 ones are the most common to describe an ellipsoid. Patches welcome if your needs go beyond that.
I don't think OCTProj4Normalize() strips the b parameter. It's just, that OGR transforms (a, b) into equivalent (a, rf) in importFromWkt(), as the WKT modelling of an ellipsoid requires those later parameters. And in exportToProj4() it will generate "+a=xxxx +b=yyyyy" 2 working examples : 1) testepsg "+proj=stere +lat_0=90 +lon_0=315 +lat_ts=70 +units=m +a=6378273 +rf=278" --> PROJ.4 rendering of [+proj=stere +lat_0=90 +lon_0=315 +lat_ts=70 +units=m +a=6378273 +rf=278] = +proj=stere +lat_0=90 +lat_ts=70 +lon_0=315 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6355329.571942446 +units=m +no_defs 2) testepsg "+proj=stere +lat_0=90 +lon_0=315 +lat_ts=70 +units=m +a=6378273 +b=6355329.571942446" --> PROJ.4 rendering of [+proj=stere +lat_0=90 +lon_0=315 +lat_ts=70 +units=m +a=6378273 +b=6355329.571942446] = +proj=stere +lat_0=90 +lat_ts=70 +lon_0=315 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6355329.571942446 +units=m +no_defs Le Friday 17 July 2009 09:16:47 Jørn Vegard Røsnes, vous avez écrit : > On Thursday 16 July 2009 20:59:55 Even Rouault wrote: > > Le Thursday 16 July 2009 10:14:27 Jørn Vegard Røsnes, vous avez écrit : > > > Hi again, > > > > > > On Wednesday 15 July 2009 13:12:38 Jørn Vegard Røsnes wrote: > > > > Hi all, > > > > > > > > can you see the problem (this works with proj4)? > > > > It works if I remove "+a=6378273" from proj4-string, but I assume the > > > > output will be wrong. > > > > > > > > ./ogr2ogr -s_srs EPSG:4326 -t_srs "+proj=stere +lat_0=90 +lon_0=315 > > > > +lat_ts=70 +units=m +a=6378273 +e=0.081816153" -f "ESRI Shapefile" > > > > gshhs_land_stere ~/download/gshhs_1.3_shapefiles/gshhs_land/ > > > > > > I have downloaded v1.6.1, added some debug and compiled > > > (--enable-debug). > > > > > > It seems that > > > > > > ogr/ogr_srs_proj4.cpp OGRSpatialReference::importFromProj4, line 847 - > > > 945 > > > > > > does not read the +e proj4 parameter (neither +f and +es), ref. page 9 > > > in proj4 doc (ftp://ftp.remotesensing.org/proj/OF90-284.pdf). > > > > > > +b and +rf is read by the code, so maybe there is a math. workaround? > > > > Yes, the a,b,e,f and rf parameters are tied by math relations. > > > > See http://www.arsitech.com/mapping/geodetic_datum. (rf is reverse > > flattening = inverse flattening) > > Yes, I found > http://en.wikipedia.org/wiki/Angular_eccentricity#Elliptic_parameters > and calculated b, yesterday. > > Then I found something I do not know if is a feature or bug. > > ogr/ogrct.cpp OCTProj4Normalize > strips away the b (, f and rf) parameter in the proj4 string. It is the > call to pszNewProj4Def = pfn_pj_get_def( psPJSource, 0 ); line 245 > that does this. > I think this is a call to the proj4 libs and it seems that the proj4 libs > removes the b parameter from the proj4 string, because proj4 is satisfied > with the a and e params. OGR seems to require a and b, e is not used by > OGR. I solved this by calling > return CPLStrdup( pszProj4Src ); > in the start of the OCTProj4Normalize function. > > Note that I haven't downloaded the proj4 source, and I just assume in the > text above. > > cheers > Jørn Vegard > > > > cheers > > > Jørn Vegard > > > > > > > All binaries (proj4, ogr2ogr) from FWTools 2.0.6 > > > > > > > > cheers > > > > Jørn Vegard > > > > _______________________________________________ > > > > gdal-dev mailing list > > > > gdal-dev@lists.osgeo.org > > > > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > > > > > _______________________________________________ > > > gdal-dev mailing list > > > gdal-dev@lists.osgeo.org > > > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
