[gdal-dev] Comparing two SRS's, different Proj4

[Rutger]

Even Rouault-2 wrote
> Le vendredi 11 mars 2016 10:58:49, Rutger a écrit :
> 
>>...
> 
> This is a bit tricky. There are 2 things to consider:
> - one of the "culprit" is ImportFromProj4(). It uses a proj.4 function
> that 
> "normalizes" the proj.4 parameters, and that may have some influence on
> +datum 
> parameters being appended a +towgs84 clause  or not depending on the
> proj4. 
> version.
> I made a fix for the WGS84 case, a few months ago in trunk (so not in
> 2.0.X), 
> so as not to happen the +towgs84=0,0,0 clause :
> https://trac.osgeo.org/gdal/changeset/29775
> - the other culprit is  ExportToProj4(). Normally the default behaviour of 
> ExportToProj4() when it sees a +towgs84 node is to remove the +datum and
> let 
> only +ellps +towgs84. I don't recall precisely the reason for this, but
> this 
> behaviour can be altered by setting the OVERRIDE_PROJ_DATUM_WITH_TOWGS84
> config 
> option/environmenet variable to NO.
> 
> I've tested on GDAL 2.0.X :
> $ OVERRIDE_PROJ_DATUM_WITH_TOWGS84=NO gdalsrsinfo '+proj=aea +lat_1=20 
> +lat_2=-23 +lat_0=0 +lon_0=25 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
> '
> 
> PROJ.4 : '+proj=aea +lat_1=20 +lat_2=-23 +lat_0=0 +lon_0=25 +x_0=0 +y_0=0 
> +datum=WGS84 +units=m +no_defs '
> 
> In trunk, no need to add OVERRIDE_PROJ_DATUM_WITH_TOWGS84=NO since due to
> the 
> first fix I mentionned ImportFromProj4() of +datum=WGS84 no longer
> generates 
> +towgs84=0,0,0 node.
> 
> Even
> 
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Even,

Thanks for fast response, setting the environment variable works very well,
so that solves it for now. In case anyone else needs this, you can set it in
Python with:
os.environ['OVERRIDE_PROJ_DATUM_WITH_TOWGS84'] = 'NO'

Which makes it valid during the Python "session", as long as python.exe is
running i guess.


Regards,
Rutger








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