[Qgis-user] Inconsistent projection parameters for EPSG:3168
Hilmy Hashim
hilmyh at gmail.com
Thu Apr 7 02:04:28 PDT 2011
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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