[gdal-dev] Intersection of two Layers

[Kai Muehlbauer]

Hi,

at the moment I calculate the intersection of two OGR Layers (A, B) by 
iterating over features/geometries (GA) of layer A and then calling 
GA.Intersection(GB) for every Feature/Geometry (GB) of B. I set a 
spatial filter for layer B with every GA. The intersections 
features/geometries are written to a result layer (C).

In my use case the features/geometries of layer B are much smaller than 
the features of layer A. Means that quite a big number of B's geometries 
are fully contained in A's geometries.

To speed things up, I check for containment GA.contains(GB). If GB is 
contained in GA, I just copy GB to C, otherwise I calculate 
GA.Intersection(GB) and write this to C.

I found that I also could use the layer intersection function 
(OGRLayer::Intersection). Unfortunately the intersection is calculated 
for every feature/geometry.

Would it be possible to extend the layer intersection function to allow 
for containment check (eg. as an option) and just copy the contained 
geometries without calculation of expensive intersection? Suggestions, 
opinions?

In my use case I get improvements of around 20% of processing time.

Cheers,
Kai