[Gdal-dev] proj4/wkt --> epsg

[Mateusz Loskot]

Frank Warmerdam wrote:
> Mateusz Loskot wrote:
>> Shoaib Burq wrote:
>>> Hi, I was just wondering if there is a way to programatically convert
>>> proj4 or wkt to and EPSG code in OSR?
>>
>> One of possibilities I see is to import SRS to OGRSpatialReference:
>>
>> char* pszWkt = "..."; // put here your SRS WKT definition
>>
>> OGRSpatialReference srs;
>> srs.exportToWkt( &pszWkt );
>>
>> const char* pszTarget = 0;
>> const char* pszAuthName = 0;
>> const char* pszAuthCode = 0;
>>
>> if (srs.IsProjected())
>>    pszTarget = "PROJCS";
>> else
>>    pszTarget = "GEOGCS";
>>
>> pszAuthName = srs.GetAuthorityName( pszTarget );
>> if( NULL != pszAuthName )
>> {
>>    if( EQUAL( pszAuthName, "EPSG" ) )
>>    {
>>       pszAuthCode = srs.GetAuthorityCode( pszTarget );
>>       if( NULL != pszAuthCode )
>>       {
>>            // XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
>>            // Here is the epsg code
>>            int epsg = atoi(pszAuthCode);
>>       }
>>    }
>> }
>>
>> Similarly, you should be able to import SRS from PROJ.4 definition using
>> OGRSpatialReference::importFromProj4().
>>
>> I've not compiled this code above, it is a copy&paste with small
>> modifications from ogr/ogr2gmlgeometry.cpp file, starting from line 235
>> where I retrieve EPSG code to save it as a value of srsName - GML
>> attribute.
> 
> Mateusz / Shoaib,
> 
> The above will work if there is an ESPG authority code in the WKT.
> Unfortunately, if you import a definition from PROJ.4 there is no
> indication of the epsg code, so there will be no epsg authority codes
> in the WKT representation.
> 
> Generally speaking there is no good way to go from PROJ.4 to EPSG codes.

Frank,

Thank you for your explanation.

Cheers
-- 
Mateusz Loskot
http://mateusz.loskot.net