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

Martin Davis mbdavis at refractions.net
Wed Sep 29 12:44:34 EDT 2010


I feel for your frustration.  Be assured that I have had very similar 
feelings for a long time!  But as you realize, this just is not an easy 
problem to solve (at least not for me, and I presume for others as well 
since no-one has popped up with a solution over the last 10 years).  
I've spent literally hundreds of hours and 10's of thousands of dollars 
working on potential solutions to this problem.  Many improvements have 
been made, such as:

- more accurate intersection compuation
- improved noding (via repeated noding)
- using snapping when topology failures are found

And I have more ideas sitting in the lab, such as Snap-Rounding, and an 
improved technique for noding.  But work goes very slowly on these, both 
because they are difficult problems to solve (and code), and because I 
don't have the luxury of working on them full-time.

It would be great if some funding could be found to allow full-time work 
on this solutions.  I'll even lower Paul's number to say 30,000 euros!


On 9/29/2010 6:31 AM, G. Allegri wrote:
> Sorry for this strong title, but I would like to open a discussion on
> this topic. There are already several tickets about TopologyException
> happening in various contexts, and I now it is not an easy to solve
> problem. We, in my company, have struggled to circumvent this frequent
> error, and we put some (few) money to let Sandro (strk) analyze it.
> The only solutions, at now, have been various workarounds that (not
> deterministically) work for some cases/datasets, but fail with others.
> Our first "meet" with this exception was due to GeomUnion operations.
> Today we face it for ST_Difference op in PostGIS, and this time no
> workaround is working.
> I anticipate the critics: put the money on the table and someone could
> invest time to solve it. Holy words, this is how foss should work. But
> I'm not the boss of my company, and I've suggested to employ
> PostGIS->GEOS in a big job... and now I have to solve this issue, with
> no extra-money.
>   If this problem cannot be solved I have to abandon PostGIS for one of
> our production environments, and that would be a pity.
> So, my reflection is: in a few weeks we have fighted, almost daily,
> with this error. Are we the only ones to get stuck in it? Have others
> found consistent,deterministic solutions?
> I would be gratefull if you can share your experience and thoughts...
> Giovanni
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Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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