Steve, when you specify a proj.4 string to GDAL/OGR, it doesn't keep it verbatim but translates it into its internal SRS model (based on WKT format). When it must pass a SRS back to proj.4, it translates from this model.
During this translation, if it detects an explicit datum known by PROJ.4, such as NAD83, it just omits the towgs84 parameter. +datum is a shortcut for specifying both +ellps and +towgs84. See this thread http://n2.nabble.com/How-to-use-towgs84-td2393158.html where this was debated. So just remove the "+datum=NAD83" parameter. The +ellps and +towgs84 will then be passed to PROJ.4. Best regards, Even _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
