Yann Chemin wrote:
Hello,
(C API)
The aim is to get a (lat,long) pair
into (projX,projY) pair from hDataset1 projection info.
Lat/long projection was defined with:
char *pszProj4 = "+proj=ll +ellps=wgs84 +datum=wgs84";
Yann,
For a geographic (long/lat) coordinate system you should be
using +proj=longlat, not +proj=ll.
OGRSpatialReferenceH hSRS;
OSRImportFromProj4(hSRS, pszProj4);
printf( "%s\n", pszProj4 );
The Import call looks fine.
Using GDALGetProjectionRef( hDataset1 ),
the raster projection info is extracted.
Here somehow the extracted projection information
should be imported into a second OGRSpatialReferenceH,
called hSRS1 for example. But I don't know how to do that.
I am confused by the C++ examples actually,
and have difficulties to find a proper C example somewhere to do that.
thanks for any help/suggestion,
Yann
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You might find the code from gdalinfo.c which does roughly the opposite
(projected dataset corners to lat/long) helpful. Some key parts are:
/* -------------------------------------------------------------------- */
/* Setup projected to lat/long transform if appropriate. */
/* -------------------------------------------------------------------- */
if( GDALGetGeoTransform( hDataset, adfGeoTransform ) == CE_None )
pszProjection = GDALGetProjectionRef(hDataset);
if( pszProjection != NULL && strlen(pszProjection) > 0 )
{
OGRSpatialReferenceH hProj, hLatLong = NULL;
hProj = OSRNewSpatialReference( pszProjection );
if( hProj != NULL )
hLatLong = OSRCloneGeogCS( hProj );
if( hLatLong != NULL )
{
CPLPushErrorHandler( CPLQuietErrorHandler );
hTransform = OCTNewCoordinateTransformation( hProj, hLatLong );
CPLPopErrorHandler();
OSRDestroySpatialReference( hLatLong );
}
if( hProj != NULL )
OSRDestroySpatialReference( hProj );
}
...
/************************************************************************/
/* GDALInfoReportCorner() */
/************************************************************************/
static int
GDALInfoReportCorner( GDALDatasetH hDataset,
OGRCoordinateTransformationH hTransform,
const char * corner_name,
double x, double y )
{
double dfGeoX, dfGeoY;
double adfGeoTransform[6];
printf( "%-11s ", corner_name );
/* -------------------------------------------------------------------- */
/* Transform the point into georeferenced coordinates. */
/* -------------------------------------------------------------------- */
if( GDALGetGeoTransform( hDataset, adfGeoTransform ) == CE_None )
{
dfGeoX = adfGeoTransform[0] + adfGeoTransform[1] * x
+ adfGeoTransform[2] * y;
dfGeoY = adfGeoTransform[3] + adfGeoTransform[4] * x
+ adfGeoTransform[5] * y;
}
else
{
printf( "(%7.1f,%7.1f)\n", x, y );
return FALSE;
}
/* -------------------------------------------------------------------- */
/* Report the georeferenced coordinates. */
/* -------------------------------------------------------------------- */
if( ABS(dfGeoX) < 181 && ABS(dfGeoY) < 91 )
{
printf( "(%12.7f,%12.7f) ", dfGeoX, dfGeoY );
}
else
{
printf( "(%12.3f,%12.3f) ", dfGeoX, dfGeoY );
}
/* -------------------------------------------------------------------- */
/* Transform to latlong and report. */
/* -------------------------------------------------------------------- */
if( hTransform != NULL
&& OCTTransform(hTransform,1,&dfGeoX,&dfGeoY,NULL) )
{
printf( "(%s,", GDALDecToDMS( dfGeoX, "Long", 2 ) );
printf( "%s)", GDALDecToDMS( dfGeoY, "Lat", 2 ) );
}
printf( "\n" );
return TRUE;
}
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
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