[gdal-dev] Intersection of two Layers

[Ari Jolma]

22.01.2016, 12:48, Kai Muehlbauer kirjoitti:
>
>
> Am 22.01.2016 um 10:52 schrieb Ari Jolma:
>> 22.01.2016, 10:06, Kai Muehlbauer kirjoitti:
>>>
>>>
>>> To quickly check if there is an improvement I used the python shapely
>>> package. Converting the outer loop geometry to an shapely prepared
>>> geometry and calling 'contains()' with the inner loop geometries to
>>> find those fully contained geometries I get an improvement of nearly
>>> 40% to the former ogr only code.
>>>
>>> As Even pointed out, there is only OGRPreparedGeometryIntersects()
>>> (GEOSPreparedIntersects) exposed within ogrgeometry.cpp. In my use
>>> case I would need GEOSPreparedContains to mimic the shapely behaviour.
>>
>> I made a small test with the attached diff, which prepares the
>> geometries of the input layer.
>>
>> The input layer had two polygons (boundaries of two Finnish
>> municipalities) and the method layer had 3091 points, all in either one
>> of the polygons.
>>
>> The improvement is ~15%.
>>
>> I think the prepared geometries could be used by default easily.
>> Prepared contains test would need addition of the respective GEOS 
>> method.
>
> Thanks Ari, I very much appreciate your efforts in testing layer 
> intersection. If the prepared contains test could be done within the 
> layer intersection then those features can "just be copied" without 
> the need of costly intersection calculation. This would give a real 
> speedup.

It seems so, I added the contains test and in this case the total 
speedup is ~80 %.

>
> So, it would need the addition of the OGRPreparedGeometryContains 
> method (GEOSPreparedContains) and then enhancing your patch.
> Would it work the way as in the attached diff? Or did I miss something?

Attached is my diff, which basically copies to add-to-result code, which 
might be done better.

>
> What are the next steps to get this feature fully implemented?

The thing is that most of the other layer methods could be enhanced this 
way, which means some more work. I believe the C++ API can be enhanced 
for version 2.1.

Ari

>
> Cheers,
> Kai
>
>
>
>
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