Thanks for the answer. Not what I wanted to hear but such is life. (And I think it makes sense now that you explain it - ie, it's not a neatly reversible translation).
It will complicate my user interface somewhat, but I think I've got an idea of how to work around it. Thanks, Nik. On 30 Aug 2014, at 3:45 am, Even Rouault <[email protected]> wrote: >>> On 8/28/2014 8:42 PM, Nik Sands wrote: >>> Hi devs, >>> >>> What is the correct way to extract the EPSG code from an >>> OGRSpatialReferenceH ? >>> >>> Currently I'm finding that the following works only for SRS of some images > and not others: >>> const char *charAuthType = OSRGetAttrValue(gdal.srcSRS, "AUTHORITY", 0); >>> const char *charSrsCode = OSRGetAttrValue(gdal.srcSRS, "AUTHORITY", 1); >>> >>> However, there is no "AUTHORITY" node in some SRSs so it doesn't work for > those images. To cater for this, I'm trying to explicitly set the authority > node using: >>> OSRAutoIdentifyEPSG(gdal.srcSRS); >>> >>> But this fails with OGRERR_UNSUPPORTED_SRS (even when it is an SRS that >>> GDAL recognises and uses well). > > Yes, this is expected. There are just a few SRS definitions that are encoded > in > it. > >>> >>> So I'm stumped... how do I reliably determine the EPSG for an >>> OGRSpatialReferenceH? > > There's no real reliable way of doing that. There are approximative methods > to > get a best match. For example you could iterate on EPSG codes with > importFromEPSG() and exportToProj4(), and compare with exportToProj4() on > your > WKT, but you can easily find situations where several EPSG SRS resolve to the > same proj4 string. > Anyway, there's currently no such ready-made heuristics method in GDAL, > although it might be useful to have one ultimately. > >>> >>> Cheers, >>> Nik. >>> >>> _______________________________________________ >>> gdal-dev mailing list >>> [email protected] >>> http://lists.osgeo.org/mailman/listinfo/gdal-dev >> >> _______________________________________________ >> gdal-dev mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/gdal-dev > > -- > Spatialys - Geospatial professional services > http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
