[geos-devel] Re: TopologyException makes GEOS/JTS very difficult to employ in my production environments...

strk strk at keybit.net
Thu Sep 30 03:49:53 EDT 2010

On Thu, Sep 30, 2010 at 09:27:23AM +0200, G. Allegri wrote:

> But many times the errors happen also with valid
> data, and that's the case, for example, in unioning. In such cases you
> cannot know before time what kind of beasts you will get through
> during the cascaded unioning.

I think I fixed that bug in GEOS trunk (the one allowing invalid results
coming out from Union operations).

Still, there are cases in which valid inputs trigger TopologyExceptions
(tracker has a few). Funding an improved-robustness-noding project
might be useful indeed.

Another idea might be figuring out a policy on dimensional collapses,
which was the cause of one case I've been looking at while inspecting
Giovanni's datasets.
In that case, the operation was succeeding in augomented-precision 
space (with common bits removed) and the result collapsed dimensionally
while re-adding common bits (loosing precision).
For polygons, such collapses result in zero-area rings or spikes.
If you know you don't care about those, you may just have them removed
rather than getting a TopologyException. This would be particularly
useful when that happens in a cascaded union operation.

I think the latter would even cost less than 30k


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