Selon Oliver Soong <osoong+g...@gmail.com>: > The attached raster is in Albers_Conic_Equal_Area on > North_American_Datum_1983. This is correctly indicated by the WKT. > The PROJ.4 string has no such datum information. This causes problems > with rgdal in R, which uses the PROJ.4 string and never receives the > datum information. > > This seems to be limited to Albers_Conic_Equal_Area and > North_American_Datum_1983, although our testing has been limited. > > > gdalinfo --version > GDAL 1.9.2, released 2012/10/08 > > gdalinfo -proj4 test.tif > [...] > Coordinate System is: > PROJCS["unnamed", > GEOGCS["NAD83", > DATUM["North_American_Datum_1983", > SPHEROID["GRS 1980",6378137,298.2572221010002, > AUTHORITY["EPSG","7019"]], > TOWGS84[0,0,0,0,0,0,0], > AUTHORITY["EPSG","6269"]], > PRIMEM["Greenwich",0], > UNIT["degree",0.0174532925199433], > AUTHORITY["EPSG","4269"]], > PROJECTION["Albers_Conic_Equal_Area"], > PARAMETER["standard_parallel_1",29.5], > PARAMETER["standard_parallel_2",45.5], > PARAMETER["latitude_of_center",23], > PARAMETER["longitude_of_center",-96], > PARAMETER["false_easting",0], > PARAMETER["false_northing",0], > UNIT["metre",1, > AUTHORITY["EPSG","9001"]]] > PROJ.4 string is: > '+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0 > +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs ' >
Yes, this is the new behaviour of GDAL since GDAL 1.8. +datum is not emitted when the TOWGS84 node is present in the WKT. Proj.4 doesn't need +datum when +ellps and +towgs84 are available. A few applications (like GRASS) seemed to depend on the presence of +datum but this has never been reliable since PROJ.4 only recognized a small proportion of datum names among all that are possible. Applications shouldn't rely on proj.4 string to build a SRS, but use the WKT string / OGRSpatialReference object instead. http://trac.osgeo.org/gdal/ticket/3450 and http://trac.osgeo.org/proj/ticket/122 for some background. You could also try setting the environmenet variable OVERRIDE_PROJ_DATUM_WITH_TOWGS84 to FALSE if you really need the old behaviour. _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev