Folks, There has been a great deal of confusion in my mind about the two EPSG variants of oblique mercator for over a decade. Lots of folks (Roger Lott, and others) have tried to explain this to me but I basically punted on it.
Mikael Rittri has recently very patiently explained it to me several times and simplified it enough that I have finally addressed it. In the past I treated EPSG projection methods 9815 and 9812 as the same thing, but in fact in PROJ.4 they need different flags - 9812 requires the +no_uoff flag. I have modified OGRSpatialReference to now differentiate these as "Hotine_Oblique_Mercator" and "Oblique_Mercator". Previously they were all known as "Hotine_Oblique_Mercator". I'm not sure how many EPSG coordinate systems are of each variant, but there seems to be well over half a dozen of each and some of them are quite important. The changes to GDAL are addressed in: http://trac.osgeo.org/gdal/ticket/2745 The primary changeset is: http://trac.osgeo.org/gdal/changeset/24091 There is also a helpful discussion of the issue in the PROJ.4 Trac: http://trac.osgeo.org/proj/ticket/104 Outstanding issues include properly handling of the Oblique_Mercator variant in the GeoTIFF code, and the ESRI translation code. I do *not* plan to back port these changes to 1.9 as they are quite disruptive. Best regards, -- ---------------------------------------+-------------------------------------- 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
