The wrong value for the false_easting for the RSO projection has been confirmed as a bug in GeoTiff: http://trac.osgeo.org/geotiff/ticket/38
*Hilmy* On Thu, Apr 7, 2011 at 5:04 PM, Hilmy Hashim <[email protected]> wrote: > I am using QGIS 1.7.0 dev version (now at revision 15677) from the OSGeo4W > suite on a Windows 7 64-bit machine. > > The proj4 string for EPSG:3168 Kertau (RSO) / RSO Malaya (m) from > Settings->Project Properties is as follows: > > +proj=omerc +lat_0=4 +lonc=102.25 +alpha=323.0257905 +k=0.99984 > +x_0=804670.24 +y_0=0 +a=6377295.664 +b=6356094.667915204 +units=m +no_defs > > Note in particular: > +alpha=323.0257905 (azimuth) > +x_0=804670.24 (false easting) > +gamma (rectified grid angle) is not defined > > I assigned an SRS for a GeoTIFF raster using GdalTools Translate (Convert > format), essentially doing a gdal_translate -a_srs EPSG:3168. > > Using GdalTools->Information (gdalinfo) I get this SRS definition: > > Driver: GTiff/GeoTIFF > ... > Coordinate System is: > PROJCS["Kertau (RSO) / RSO Malaya (m)", > GEOGCS["Kertau (RSO)", > DATUM["Kertau_RSO", > SPHEROID["Everest 1830 (RSO > 1969)",6377295.664,300.8017000000015, > AUTHORITY["EPSG","7056"]], > AUTHORITY["EPSG","6751"]], > PRIMEM["Greenwich",0], > UNIT["degree",0.0174532925199433], > AUTHORITY["EPSG","4751"]], > PROJECTION["Hotine_Oblique_Mercator"], > PARAMETER["latitude_of_center",4], > PARAMETER["longitude_of_center",102.25], > PARAMETER["azimuth",323.0257905], > PARAMETER["rectified_grid_angle",323.1301023611111], > PARAMETER["scale_factor",0.99984], > PARAMETER["false_easting",0], > PARAMETER["false_northing",0], > UNIT["metre",1, > AUTHORITY["EPSG","9001"]], > AUTHORITY["EPSG","3168"]] > ... > > Notice that the "false easting" parameter is 0 instead of the correct value > of 804670.24 as found in proj4. The azimuth value is correct and there is > also a rectified_grid_angle value. > > Looking in OSGeo4W\share\epsg_csv\pcs.csv, I see the following values for > 3168: > > PARAMETER_VALUE_1: 804670.24 > PARAMETER_VALUE_5: 323.01328458 > PARAMETER_VALUE_6: 323.07483685 > > Now the false easting value is correct, while the azimuth and > rectified_skew_angle are different. > > So where is Gdal in QGis getting it's parameters from? > > > > *Hilmy* >
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