Vjylku

I am looking for an easy way to extract a raster's extent in python.

Currently, I am using gdalinfo and then parsing out the corner coordinates. The problem with this approach is that gdalinfo is not consistent in how it reports the corner coordinates. I am working with a variety of file types (hdf, tif, img, asc, etc). I need the extent to be in decimal degrees (or DMS - that I can convert to decimal degrees).

This is being used with a PostgreSQL database so I have access to any PostGIS function, gdal, or ArcGIS, although I would prefer a function that does not involve ArcGIS unless it is fast (I am trying to index a large number of files, frequently). It can be run on either Windows or Unix.

Thank you,
Kevin

Probably the python port of gdalinfo would help you. You can see at the top of the file that all the coordinates are reported using the GDALInfoReportCorner method:

#/* -------------------------------------------------------------------- */

#/*      Report corners.                                                 */

#/* -------------------------------------------------------------------- */

print( "Corner Coordinates:" )

GDALInfoReportCorner( hDataset, hTransform, "Upper Left", 

                      0.0, 0.0 );

GDALInfoReportCorner( hDataset, hTransform, "Lower Left", 

                      0.0, hDataset.RasterYSize);

GDALInfoReportCorner( hDataset, hTransform, "Upper Right", 

                      hDataset.RasterXSize, 0.0 );

GDALInfoReportCorner( hDataset, hTransform, "Lower Right", 

                      hDataset.RasterXSize, 

                      hDataset.RasterYSize );

GDALInfoReportCorner( hDataset, hTransform, "Center", 

                      hDataset.RasterXSize/2.0, 

                      hDataset.RasterYSize/2.0 );

you can change the method itself which is implemented at the bottom:

#/************************************************************************/

#/*                        GDALInfoReportCorner()                        */

#/************************************************************************/



def GDALInfoReportCorner( hDataset, hTransform, corner_name, x, y ):





    line = "%-11s " % corner_name



#/* -------------------------------------------------------------------- */

#/*      Transform the point into georeferenced coordinates.             */

#/* -------------------------------------------------------------------- */

    adfGeoTransform = hDataset.GetGeoTransform(can_return_null = True)

    if adfGeoTransform is not None:

        dfGeoX = adfGeoTransform[0] + adfGeoTransform[1] * x 

            + adfGeoTransform[2] * y

        dfGeoY = adfGeoTransform[3] + adfGeoTransform[4] * x 

            + adfGeoTransform[5] * y



    else:

        line = line + ("(%7.1f,%7.1f)" % (x, y ))

        print(line)

        return False



#/* -------------------------------------------------------------------- */

#/*      Report the georeferenced coordinates.                           */

#/* -------------------------------------------------------------------- */

    if abs(dfGeoX) < 181 and abs(dfGeoY) < 91:

        line = line + ( "(%12.7f,%12.7f) " % (dfGeoX, dfGeoY ))



    else:

        line = line + ( "(%12.3f,%12.3f) " % (dfGeoX, dfGeoY ))



#/* -------------------------------------------------------------------- */

#/*      Transform to latlong and report.                                */

#/* -------------------------------------------------------------------- */

    if hTransform is not None:

        pnt = hTransform.TransformPoint(dfGeoX, dfGeoY, 0)

        if pnt is not None:

            line = line + ( "(%s," % gdal.DecToDMS( pnt[0], "Long", 2 ) )

            line = line + ( "%s)" % gdal.DecToDMS( pnt[1], "Lat", 2 ) )



    print(line)



    return True

Make it print whatever you want :)

With Arcgis 9.3 I believe it is consistent just WHEN the rasters are georeferenced!.
Then after creating geoprocessing object u can reach it easily with Extent object.

extentofXmin= gp.Describe(rastersource).Extent.Xmin #this is a topleft corner

The other corners respectively reached by Ymin, Xmax, Ymax.
You can see the corner situation in RasterClip in Arcgis like in this img: http://i.stack.imgur.com/aVEWV.png

I believe you've almost accomplished your goal parsing gdalinfo. The reason why you have not only decimal degrees is that your data seems to have several CRS. But gdalinfo will provide you with the information of the CRS of the given layer. Only thing you need to do is to create geometry from extent, transform it to the needed CRS (using TransformTo OGR function for example) and extract coordinates once again.

Also you may consider using gdaltindex. Maybe you will need to handle rasters with different CRS somehow, but I believe this will not be a great deal to write proper script. You will get a shp-file with rasters boundaries (and raster names and paths). Transform it to needed CRS and extract corner coordinates of the features.