[gdal-dev] Gamma parameter not set in proj4 string for RSO projections

Even Rouault even.rouault at mines-paris.org
Thu Apr 14 03:27:29 EDT 2011


Selon Hilmy Hashim <hilmyh at gmail.com>:

> Sorry to bring this up again. I've been looking for why epsg_tr.py -proj4 is
> not including the +gamma (RectifiedToSkew angle) parameter for the
> +proj=omerc projection as used in EPSG:3168, EPSG:3375, etc. It seems that
> it is not set in
> https://svn.osgeo.org/fdo/trunk/Thirdparty/gdal/ogr/ogr_srs_proj4.cpp:

--> You are not looking to the right repository (the one above is an import of
an older GDAL version by the FDO project). The main GDAL repository is located
at http://svn.osgeo.org/gdal/trunk.

I can see that a fix for the gamma parameter in
http://trac.osgeo.org/gdal/changeset/18950. This is in GDAL 1.8.0 and the
testepsg utility gives :

PROJ.4 rendering of [EPSG:3168] = +proj=omerc +lat_0=4 +lonc=102.25 +alpha=323.0
257905 +k=0.99984 +x_0=804670.24 +y_0=0 +gamma=323.1301023611111 +a=6377295.664
+b=6356094.667915204 +units=m +no_defs

>
> else if( EQUAL(pszProj,"omerc") )
>
>     {
>         SetHOM( OSR_GDV( papszNV, "lat_0", 0.0 ),
>                 OSR_GDV( papszNV, "lonc", 0.0 ),
>                 OSR_GDV( papszNV, "alpha", 0.0 ),
>                 0.0, /* ??? */
>                 OSR_GDV( papszNV, "k", 1.0 ),
>                 OSR_GDV( papszNV, "x_0", 0.0 ),
>                 OSR_GDV( papszNV, "y_0", 0.0 ) );
>     }
>
> ...
>
>
>         else
>         {
>             sprintf( szProj4+strlen(szProj4),
>                      "+proj=omerc +lat_0=%.16g +lonc=%.16g +alpha=%.16g"
>                      " +k=%.16g +x_0=%.16g +y_0=%.16g ",
>                      GetNormProjParm(SRS_PP_LATITUDE_OF_ORIGIN,0.0),
>                      GetNormProjParm(SRS_PP_CENTRAL_MERIDIAN,0.0),
>                      GetNormProjParm(SRS_PP_AZIMUTH,0.0),
>                      GetNormProjParm(SRS_PP_SCALE_FACTOR,1.0),
>                      GetNormProjParm(SRS_PP_FALSE_EASTING,0.0),
>                      GetNormProjParm(SRS_PP_FALSE_NORTHING,0.0) );
>         }
>
> There seems to be some uncertainty about this parameter. How can this be
> resolved and how can I help?
>
> Thanks.
>
> *Hilmy*
>




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