[gdal-dev] Failed to process SRS definition

[Jørn Vegard Røsnes]

On Thursday 16 July 2009 20:59:55 Even Rouault wrote:
> Le Thursday 16 July 2009 10:14:27 Jørn Vegard Røsnes, vous avez écrit :
> > Hi again,
> >
> > On Wednesday 15 July 2009 13:12:38 Jørn Vegard Røsnes wrote:
> > > Hi all,
> > >
> > > can you see the problem (this works with proj4)?
> > > It works if I remove "+a=6378273" from proj4-string, but I assume the
> > > output will be wrong.
> > >
> > > ./ogr2ogr -s_srs EPSG:4326 -t_srs "+proj=stere +lat_0=90 +lon_0=315
> > > +lat_ts=70 +units=m +a=6378273 +e=0.081816153" -f "ESRI Shapefile"
> > > gshhs_land_stere ~/download/gshhs_1.3_shapefiles/gshhs_land/
> >
> > I have downloaded v1.6.1, added some debug and compiled (--enable-debug).
> >
> > It seems that
> >
> > ogr/ogr_srs_proj4.cpp OGRSpatialReference::importFromProj4, line 847 -
> > 945
> >
> > does not read the +e proj4 parameter (neither +f and +es), ref. page 9 in
> > proj4 doc (ftp://ftp.remotesensing.org/proj/OF90-284.pdf).
> >
> > +b and +rf is read by the code, so maybe there is a math. workaround?
>
> Yes, the a,b,e,f and rf parameters are tied by math relations.
>
> See http://www.arsitech.com/mapping/geodetic_datum. (rf is reverse
> flattening = inverse flattening)
>
Yes, I found 
http://en.wikipedia.org/wiki/Angular_eccentricity#Elliptic_parameters
and calculated b, yesterday.

Then I found something I do not know if is a feature or bug.

ogr/ogrct.cpp OCTProj4Normalize 
strips away the b (, f and rf) parameter in the proj4 string. It is the call 
to  pszNewProj4Def = pfn_pj_get_def( psPJSource, 0 ); line 245 
that does this. 
I think this is a call to the proj4 libs and it seems that the proj4 libs 
removes the b parameter from the proj4 string, because proj4 is satisfied 
with the a and e params. OGR seems to require a and b, e is not used by OGR.
I solved this by calling
return CPLStrdup( pszProj4Src );
in the start of the OCTProj4Normalize function.

Note that I haven't downloaded the proj4 source, and I just assume in the text 
above.

cheers
Jørn Vegard



> > cheers
> > Jørn Vegard
> >
> > > All binaries (proj4, ogr2ogr) from FWTools 2.0.6
> > >
> > > cheers
> > > Jørn Vegard
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