[gdal-dev] epsg_tr.py in reverse?

Moskovitz, Bob Bob.Moskovitz at conservation.ca.gov
Mon Mar 3 12:43:22 EST 2008


Thanks Frank, I'll take play with this last idea.

> -----Original Message-----
> From: Frank Warmerdam [mailto:warmerdam at pobox.com]
> Sent: Friday, February 29, 2008 8:11 PM
> To: Moskovitz, Bob
> Cc: Gdal-Dev (E-mail 2)
> Subject: Re: [gdal-dev] epsg_tr.py in reverse?
> 
> 
> Moskovitz, Bob wrote:
> > Hello All,
> > 
> > I would like to find a utility that would allow you to find 
> the EPSG code
> > given a proj4 string.  Sort of a epsg_tr.py in reverse.  
> Can a utility be
> > written with the gdal api to do that?
> 
> Bob,
> 
> You could walk the whole list of EPSG coordinate systems, import each
> to an OGRSpatialReference object, and then use the OGRSpatialReference
> IsSame() method to compare it to an OGRSpatialReference imported from
> a PROJ.4 definition.  This would, in theory, let you find a 
> match.  But
> in practice this is computationally expensive and the 
> IsSame() method is
> flakey in a number of regards (too sensitive to some 
> differences such as
> order, and not aware of other differences like prime meridian).
> 
> Another approach would be to convert them all to PROJ.4 
> format and do exact
> string comparisons.  You would need to convert the original 
> (target) PROJ.4
> definition to WKT and convert it back to PROJ.4 too, so it would be
> "normalized" to the style of PROJ.4 produced by OGR.
> 
> This would likely work fairly well, but would still be sensitive to
> different numeric precision for parameters.
> 
> Best regards,
> -- 
> ---------------------------------------+----------------------
> ----------------
> I set the clouds in motion - turn up   | Frank Warmerdam, 
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, 
http://osgeo.org



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