GDAL Python Creating Contourlines

Question

I'd like to generate contourlines from a SRTM image within Python. It seems to calculate but if I want to add my contourlines nothing shows up and the attribute table is empty as well. Please take a look at my code:

    from osgeo import gdal, gdal_array
    from osgeo.gdalconst import *
    from numpy import *
    from osgeo import ogr

    #Read in SRTM data
    indataset1 = gdal.Open( src_filename_1, GA_ReadOnly)
    in1 = indataset1.GetRasterBand(1)
    
    #Generate layer to save Contourlines in
    ogr_ds = ogr.GetDriverByName("ESRI Shapefile").CreateDataSource(dst_filename)
    contour_shp = ogr_ds.CreateLayer('contour')
    
    field_defn = ogr.FieldDefn("ID", ogr.OFTInteger)
    contour_shp.CreateField(field_defn)
    field_defn = ogr.FieldDefn("elev", ogr.OFTReal)
    contour_shp.CreateField(field_defn)
    
    #Generate Contourlines
    gdal.ContourGenerate(in1, 100, 0, [], 0, 0, contour_shp, 0, 1)
    ogr_ds.Destroy()

Field ID and field elevation seem to be empty, but the contour_shape file is fairly huge ~100MB.

Any idea what might went wrong?

Update: I got it! I forgot to close the datasource with: ogr_ds.Destroy()

Answer 1

Don't use the Destroy() method, as described in the GDAL/OGR Python Gotchas.

To save and close a dataset, dereference the variable, and optionally delete it.

I typically use this at the end to save/close either a GDAL or OGR dataset:

ogr_ds = None
del ogr_ds