[Qgis-user] Inconsistent projection parameters for EPSG:3168

[Hilmy Hashim]

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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