[postgis-users] Topological Exceptions

[Obe, Regina]

Yes an ERROR() geometry even better. I suppose that is not part of the
OGC specs. 

I was thinking that if it did at least return an empty collection - then
I could inspect the ones that returned an empty collection for issues or
simply throw them out with a filter if I didn't want to be bothered with
them, but an ERROR() geometry would be better to differentiate from
truly empty collections.

Thanks,
Regina

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
Ramsey
Sent: Wednesday, March 12, 2008 1:18 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Topological Exceptions

Hard. An "ERROR()" geometry type is almost called for, so that you can
run the whole set and actual inspect post-facto which ones failed.
The most annoying part of the current behavior for me is the
difficulty tracking down the problematic pair of geometries.  I think
you're right, the current fail-and-stop behavior causes more problems
than it solves.

On 3/11/08, Obe, Regina <robe.dnd at cityofboston.gov> wrote:
>
>
> I've been doing a lot of work using ST_Intersection, ST_Difference,
ST_Union
> etc to cut out slices of geometries I don't want and slicing up
geometries
> into smaller pieces, reunioning etc.
>
> I've been running into a lot of Topological Exceptions of the form
directed
> Edge this and non-noded that.  For the most part I've been able to
overcome
> these by slicing things smaller or skipping over problem regions (e.g.
areas
> where the difference is a line or point or something of that sort).
>
> I think a lot of people have run into the same issues and have gotten
> frustrated and there doesn't seem to be a simple solution suggested to
> overcome these.
>
> Is there any way we can change (add overloaded functions or some
setting
> parameter) - that take additional parameters to simply ignore these
errors
> that says return empty collection or NULL when a GEOS error is thrown.
That
> way I can simply ignore these and throw them out of my equation and
move on.
>
> Just a thought.  I'm sure my suggestion is rather simple-minded and
I'm sure
> I'm missing some reason of why this is not feasible.  An explanation
of why
> my suggestion is stupid at anyrate would be nice.
>
> Thanks,
> Regina
>
>
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