Is there a way to get at C's OGRLayer.Intersection() or OGRLayer.Clip() in Python?

Question

I am working with OGR in Python and noticed that the C libraries have useful Intersection() and Clip() functions as part of the Layer class. Is there any way to get at these functions in Python? I know that these functions exist on the Geometry level but I'm looking specifically at the Layer. Thanks!

Answer 1

A layer is composed of one or several geometries. For the intersection of layers, you must iterate through each layer geometries. With shapely it is easy, example with two shapefiles:

from osgeo import ogr
from shapely.wkb import loads
from shapely.geometry import *
# first layer, a polygon shapefile
first = Polygon()
# open shapefile
source1 = ogr.Open("test1.shp")
layer1 = source1.GetLayer()
# combination of all the geometries of the layer in a single shapely object
for element in layer1:
   geom = loads(element.GetGeometryRef().ExportToWkb())
   first = first.union(geom)    
# second layer, a polygon shapefile
two = Polygon()
source2 = ogr.Open("test2.shp")
layer2 = source2.GetLayer()
for element in layer2:
   geom = loads(element.GetGeometryRef().ExportToWkb())
   two = two.union(geom)

# intersection between the two layers 
print first.intersection(two).wkt

It is possible to use the same type of treatment for Clip(). Another solution is provided by Creating a little clipbox for your GIS projects in Python

Answer 2

Yes. They are exposed in the bindings:

>>> from osgeo import ogr

>>> help(ogr.Layer.Intersection)
Help on method Intersection in module osgeo.ogr:

Intersection(self, *args, **kwargs) unbound osgeo.ogr.Layer method
    Intersection(self, Layer method_layer, Layer result_layer, char options = None, 
    GDALProgressFunc callback = None, void callback_data = None) -> OGRErr

>>> help(ogr.Layer.Clip)
Help on method Clip in module osgeo.ogr:

Clip(self, *args, **kwargs) unbound osgeo.ogr.Layer method
Clip(self, Layer method_layer, Layer result_layer, char options = None, 
    GDALProgressFunc callback = None, void callback_data = None) -> OGRErr

I am guessing you need GEOS support built into GDAL and confirmed:

http://gdal.org/ogr/classOGRLayer.html#ac189f54996c2d6fd769889ec99e0f48a

and

http://gdal.org/ogr/classOGRLayer.html#a56d7ee3b2020e53c730d67ee4f1e2fb6