[geos-devel] finding intersection of LineString and large list of Polygon's

[TazMainiac]

Thanks - RTree looks like what I need.

Taz

On Tue, Feb 28, 2017 at 10:12 AM, Forrest Williams <
forrest.williams at gmail.com> wrote:

> First thought would be to use something like RTree
> <https://github.com/Toblerity/rtree> to build an index on the polygons.
>
> If you didn't want to go down the RTree route and stuck to the iterative
> method, you could speed things up by "preparing
> <https://docs.djangoproject.com/en/1.10/ref/contrib/gis/geos/#django.contrib.gis.geos.GEOSGeometry.prepared>" the
> linestring (and possibly preparing the polygons as well beforehand, but not
> sure if you're thrashing at that point, I'd say play around with it).
>
>
> Forrest W.
>
> On Tue, Feb 28, 2017 at 9:30 AM, TazMainiac <TazMainiac at gmail.com> wrote:
>
>> Hi,
>>
>>   I'm not sure if this is the right mailing list for this or not - let me
>> know if I should post somewhere else.
>>
>>   I'm using GEOS (3.5.0) via the Django (1.6.7) Python wrappers.  Under
>> Cygwin currently but will be on Linux later.
>>
>>   I have a large list (1000's) of Polygons some of which overlap.  What
>> is the most efficient way to find which polygons in the list intersect with
>> a LineString?
>>
>>   I would have thought that turning the list of Polygon's into a
>> MultiPolygon, then calling MultiPolygon.intersection with the line segment
>> would give me the polygon that the line segment intersected on.  This does
>> work, but it just returns the line segment itself.  I'm trying to go the
>> other way.
>>
>>   I was hoping for a faster mechanism than just iterating over the
>> original polygon list and calling intersect's on each.
>>
>>   I'm new to GEOS so please forgive me if I'm using incorrect terminology.
>>
>> Thanks,
>> Taz
>>
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>
>
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