[geos-devel] Progress on #837 - TopologyException in UnaryUnion

[Daniel Baston]

Either way, the union of a polygonal coverage is a common special case that
would benefit from having its own algorithm. I implemented this for PostGIS
a couple of years ago, though there didn't seem to be much interest at the
time [1]. It's probably a better fit for GEOS anyway. I wrote a fairly ugly
Java implementation several years ago [2] that I could re-do to take
advantage of recent polygonizer improvements and bring into GEOS.

Dan

[1] https://lists.osgeo.org/pipermail/postgis-devel/2016-April/025784.html
[2]
https://github.com/dbaston/CoverageOp/tree/master/src/main/java/org/dbaston/coverageop

On Tue, Apr 16, 2019 at 11:06 AM Martin Davis <mtnclimb at gmail.com> wrote:

> That's good to know, Darafei.   Can you provide a data example that we can
> use for doing performance testing?
>
> I'm not seeing that JTS buffer(0) is slower than union() on a random
> triangulation.  So perhaps either your dataset has some different
> characteristic, or possibly GEOS buffer has different performance
> characteristics to JTS.
>
> On Tue, Apr 16, 2019 at 5:27 AM Darafei "Komяpa" Praliaskouski <
> me at komzpa.net> wrote:
>
>> Hello,
>>
>>
>>> Ultimately I think the ideal approach is going to be abandoning
>>> CascadedUnion and switch to a full union algorithm (which will essentially
>>> be the same as running buffer(0).  This should have very good performance.
>>>
>>
>>  We're using PostGIS's ST_Union to dissolve a clipped TIN into a polygon.
>> Current ST_Union implementation handles this measurably faster than
>> ST_Buffer(ST_Collect(geom),0). Please keep this case in mind.
>>
>>
>> --
>> Darafei Praliaskouski
>> Support me: http://patreon.com/komzpa
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