[geos-devel] Clip and Union --> is my implementation correct?
bontepaarden at gmail.com
Tue Jan 21 07:32:26 PST 2020
Thanks for the answer and sorry for the late reply.
Because we couldn't do a quick magic trick we had to move on.
But now I'm at a similar point.
Again I have two large polygons files that I want to clip.
This is very slow. In fact, I have never succeeded because after 6+ hours I
canceled the process.
You mentioned a new function could be added to GEOS for quicker clipping of
Is that still the case? If so how much budget would be needed to get this
It is quite a showstopper for us right now and I could gather some funding
Op di 15 okt. 2019 om 20:01 schreef Martin Davis <mtnclimb at gmail.com>:
> This sounds like a classic polygon coverage overlay operation?
> The "obvious" way to do this in GEOS is by using the overlay operations.
> However, these work on pairs of geometries only, which means that (a) it's
> a bit complicated to compute a full polygon coverage overlay and (b) this
> tends to be quite slow.
> The other way to do this in GEOS is to node the linework of the input
> coverages (GEOSUnion can do this), polygonize the linework, generate
> interior points for all resulting polygons, and then determine the
> parentage of each resultant by using point-in-polygon tests against the
> input coverages.
> This is a fair amount of complex code. But it should be faster (at least,
> if spatial indexes are used where appropriate).
> Perhaps we can add a function into GEOS to perform this operation at some
> On Tue, Oct 15, 2019 at 1:06 AM Paul Meems <bontepaarden at gmail.com> wrote:
>> Hi List,
>> I have a large shapefile (land use) with a lot of small shapes (392k).
>> I also have a smaller shapefile (catchments) with larger shapes (2.5k).
>> The smaller shapefile overlaps the larger shapefile in the center.
>> I need to create a new shapefile (expected number of shapes is several
>> 100k) that have the values of the land use and the catchments combined.
>> Currently, I'm doing a GEOSClip() of the land use by the catchment first
>> and then a GEOSUnion of the clipped result and the catchment.
>> This is a bit slow. The clipping already takes 40 minutes.
>> Am I using the right approach or should I use a different one?
>> Extra info. I'm using MapWinGIS (C++) which includes GDAL and GEOS.
>> This is the implementation of GEOSClip:
>> It was created years ago. Perhaps the implementation can/should be
>> optimized as well.
>> Paul Meems
>> geos-devel mailing list
>> geos-devel at lists.osgeo.org
> geos-devel mailing list
> geos-devel at lists.osgeo.org
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