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

[Even Rouault]

Selon Hilmy Hashim <hilmyh at gmail.com>:

> Merci Even,
>
> Didn't know which one is the effective code, there are so many versions
> around. It's good to know that changes have been made.
>
> I'm using QGis 1.7 dev and the About say it's using GDAL/OGR 1.8.0. How come
> the +gamma is not included there?

I know they have updated very recently their srs.db to sync it with GDAL 1.8.0.
Perhaps you should also update to the latest svn version of qgis ?

A comment in the GDAL code also shows that the +gamma parameter is only
understood by PROJ 4.8.0 (so the svn version as 4.8.0 is unreleased yet).

But one thing is definitely weird and should be investigated first : epsg_tr.py
-proj4 3168 *should* show the +gamma parameter (whatever your proj version is).
If you don't see it, it's a clear sign you don't use GDAL 1.8.0.

What does epsg_tr.py --version return ?

>
> Regards
>
> *Hilmy*
>
>
> On Thu, Apr 14, 2011 at 3:27 PM, Even Rouault
> <even.rouault at mines-paris.org>wrote:
>
> > 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*
> > >
> >
> >
> >
>