[postgis-users] Topology Issue Reported by Query but Not Identified with ST_IsValid

[Michael Treglia]

That did the Trick - Thanks!

I do have a quick question on this though, largely out of curiousity - when
I did it with the ST_Collect, it ran for ~3 hours before throwing the
error, whereas when I changed it to ST_Union, it ran to completion in ~7
minutes. Any guess why it took so long to identify the topology issues?

(I'll note that when I have the SQL right, I'm always impressed at how fast
PostGIS is for pretty giant datasets).

Thanks again,
mike

On Fri, May 27, 2016 at 8:47 AM, Michael Treglia <mtreglia at gmail.com> wrote:

> Ah, I see - Thanks Regina! I was wondering if it was something like that,
> as the area identified it with the issue definitely had lots of adjacencies.
>
> I'll give that a try and report back,
> Best,
> Mike
>
>
> On Fri, May 27, 2016 at 12:47 AM, Regina Obe <lr at pcorp.us> wrote:
>
>> Try replacing your ST_Collect call with ST_Union.
>>
>>
>>
>> ST_Collect when used with polygons will create invalid multipolygons
>> since it just collects them up, and if they are adjacent, it's not a valid
>> multipolygon.
>>
>>
>>
>> Hope that helps,
>>
>> Regina
>>
>> http://www.postgis.us
>>
>> http://postgis.net
>>
>>
>>
>>
>>
>>
>>
>> *From:* postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] *On
>> Behalf Of *Michael Treglia
>> *Sent:* Thursday, May 26, 2016 10:34 PM
>> *To:* PostGIS Users Discussion <postgis-users at lists.osgeo.org>
>> *Subject:* [postgis-users] Topology Issue Reported by Query but Not
>> Identified with ST_IsValid
>>
>>
>>
>> Hi All,
>>
>>
>>
>> I was running a query involving ST_Difference between two multipolygon
>> layers, and a while in, it threw this message:
>>
>> ERROR: GEOSDifference: TopologyException: side location conflict at
>> 919670.1768945494 140665.82566365649
>>
>>
>>
>> However, I previously ran ST_MakeValid, and ST_IsValid doesn't report any
>> objects with problems. Is there something I'm missing, or something else I
>> need to check? (Apologies is this is just a naive question - still learning
>> my way around PostGIS).
>>
>>
>>
>> And in case it helps, here's my SQL:
>>
>>
>>
>> CREATE TABLE SI_Unclaimed AS
>>
>> SELECT gid, COALESCE(ST_Difference(geom_2263, (SELECT
>> ST_Collect(b.geom_2263)
>>
>>                                          FROM citywide_basedata.parcels15
>> b
>>
>>                                          WHERE ST_Intersects(a.geom_2263,
>> b.geom_2263)
>>
>>                                          )), a.geom_2263)
>>
>> FROM citywide_basedata.boroughs_nowater a where boroname like 'Staten
>> Island';
>>
>>
>>
>> Thanks!
>>
>> Mike
>>
>> _______________________________________________
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>>
>
>
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