Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[BladeOfLight16]

On Tue, Feb 3, 2015 at 11:28 AM, BladeOfLight16 
wrote:

> I'm trying to create a polygon overlay. The basic process is relatively
> simple: 1) Get the boundaries 2) Union the boundaries to node the
> linestrings 3) Polygonize the noded outlines 4) Filter out holes using a
> contains or intersects test. The problem I'm running into is that I'm
> getting "GEOSUnaryUnion: TopologyException: found non-noded intersection
> between LINESTRING" errors from ST_Union.
>

>
[a lot snipped]
>

I haven't seen any response to this. I was just wondering if anyone else
had a chance or intentions to look this over. Granted, it's pretty long and
involved (sorry for that), but I thought all the details I included were
important. I do know it went through the mailing list; someone on IRC
helped me find it in the... I guess it's not the archives; I don't know
what it's called. But the online browsing mechanism. Thanks to anyone who's
taking a look.
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Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[John Abraham]

Well I could say that using PostGIS ST_Intersects with "messy data" always 
seems to give me TopologyExceptions.  I've had luck with various combinations 
of ST_SnapToGrid and ST_Buffer(0), but with messy data there always seems to be 
some weird case that requires manually edits.  Sorry to be the bearer of bad 
news.  Frankly, I don't understand why the GEOS library has to throw that 
error. 

I would encourage you to isolate particular problems and file bug reports.  
Improvements in GEOS to eliminate the underlying error(s) would certainly be 
welcome.  

--
John Abraham

> On Feb 8, 2015, at 1:43 PM, BladeOfLight16  wrote:
> 
> On Tue, Feb 3, 2015 at 11:28 AM, BladeOfLight16  > wrote:
> I'm trying to create a polygon overlay. The basic process is relatively 
> simple: 1) Get the boundaries 2) Union the boundaries to node the linestrings 
> 3) Polygonize the noded outlines 4) Filter out holes using a contains or 
> intersects test. The problem I'm running into is that I'm getting 
> "GEOSUnaryUnion: TopologyException: found non-noded intersection between 
> LINESTRING" errors from ST_Union. 
>  
> [a lot snipped] 
> 
> I haven't seen any response to this. I was just wondering if anyone else had 
> a chance or intentions to look this over. Granted, it's pretty long and 
> involved (sorry for that), but I thought all the details I included were 
> important. I do know it went through the mailing list; someone on IRC helped 
> me find it in the... I guess it's not the archives; I don't know what it's 
> called. But the online browsing mechanism. Thanks to anyone who's taking a 
> look.
> ___
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> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users

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Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[Paolo Cavallini]

Il 09/02/2015 02:31, John Abraham ha scritto:
> Well I could say that using PostGIS ST_Intersects with "messy data"
> always seems to give me TopologyExceptions.  I've had luck with various
> combinations of ST_SnapToGrid and ST_Buffer(0), but with messy data
> there always seems to be some weird case that requires manually edits.

Hi John,
have you tried ST_MakeValid?
All the best.

-- 
Paolo Cavallini - www.faunalia.eu
QGIS & PostGIS courses: http://www.faunalia.eu/training.html
*New course* "QGIS for naturalists":
http://www.faunalia.eu/en/nat_course.html
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Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[BladeOfLight16]

On Sun, Feb 8, 2015 at 9:31 PM, John Abraham  wrote:

> Well I could say that using PostGIS ST_Intersects with "messy data" always
> seems to give me TopologyExceptions.  I've had luck with various
> combinations of ST_SnapToGrid and ST_Buffer(0), but with messy data there
> always seems to be some weird case that requires manually edits.  Sorry to
> be the bearer of bad news.  Frankly, I don't understand why the GEOS
> library has to throw that error.
>
> I would encourage you to isolate particular problems and file bug
> reports.  Improvements in GEOS to eliminate the underlying error(s) would
> certainly be welcome.
>

That's pretty much what my e-mail does; it even includes a sample database
to reproduce the issue. I brought it up here in case some discussion or
slimming down needed/could be done before filing a bug report, and to be
extra sure that it's a GEOS issue and not a PostGIS once, given the
complexity of the query I'm running.
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Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[Sandro Santilli]

On Tue, Feb 03, 2015 at 11:28:35AM -0500, BladeOfLight16 wrote:

> https://drive.google.com/file/d/0B_6I7kRgE8teVUpha2Q4ZlNDMWs/view?usp=sharing.

...

> DO $$
> DECLARE problem_row error_generating_polygons%ROWTYPE;
> BEGIN
>   FOR problem_row IN (SELECT * FROM error_generating_polygons) LOOP
> BEGIN
>   PERFORM ST_Union(ST_Boundary(geom))
>   FROM UNNEST(problem_row.polygons) p (geom);
>   RAISE NOTICE 'geom_set_id % succeeded', problem_row.geom_set_id;
> EXCEPTION
>   WHEN OTHERS THEN
> RAISE NOTICE 'Error for geom_set_id % (Code %): %',
> problem_row.geom_set_id, SQLSTATE, SQLERRM;
> END;
>   END LOOP;
> END
> $$;

First of all I confirm it still happens with GEOS="3.5.0dev-CAPI-1.9.0 r4038".
Second, I took a look at a random set (geom_set_id=1) and I found it pretty
big. That's to say you could probably further reduce the dataset for the
ticket. That set contains 109 polygons, I can get the error by attempting
to union the boundaries of the first 40 in that set, and I'm sure you can
further reduce the input.

So my suggestion:
 
 1) file the ticket
 2) attach the _smallest_ input that reproduces the problem

About ST_IsValid: lines are always valid, so there's no need to test.
Most likely this is a robustness issue failing to deal with very close
but not equal lines.

NOTE: I've tried my reduced input (~40) geoms against the topology builder
and it also resulted in errors, until I specified a tolerance of 1e-4.

--strk; 

  ()   Free GIS & Flash consultant/developer
  /\   http://strk.keybit.net/services.html
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Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[Rémi Cura]

Hey Sandro,
this is a precision related issue,
coordinates are way too big and should be translated.
Cheers,
Rémi-C

2015-02-09 12:25 GMT+01:00 Sandro Santilli :

> On Tue, Feb 03, 2015 at 11:28:35AM -0500, BladeOfLight16 wrote:
>
> >
> https://drive.google.com/file/d/0B_6I7kRgE8teVUpha2Q4ZlNDMWs/view?usp=sharing
> .
>
> ...
>
> > DO $$
> > DECLARE problem_row error_generating_polygons%ROWTYPE;
> > BEGIN
> >   FOR problem_row IN (SELECT * FROM error_generating_polygons) LOOP
> > BEGIN
> >   PERFORM ST_Union(ST_Boundary(geom))
> >   FROM UNNEST(problem_row.polygons) p (geom);
> >   RAISE NOTICE 'geom_set_id % succeeded', problem_row.geom_set_id;
> > EXCEPTION
> >   WHEN OTHERS THEN
> > RAISE NOTICE 'Error for geom_set_id % (Code %): %',
> > problem_row.geom_set_id, SQLSTATE, SQLERRM;
> > END;
> >   END LOOP;
> > END
> > $$;
>
> First of all I confirm it still happens with GEOS="3.5.0dev-CAPI-1.9.0
> r4038".
> Second, I took a look at a random set (geom_set_id=1) and I found it pretty
> big. That's to say you could probably further reduce the dataset for the
> ticket. That set contains 109 polygons, I can get the error by attempting
> to union the boundaries of the first 40 in that set, and I'm sure you can
> further reduce the input.
>
> So my suggestion:
>
>  1) file the ticket
>  2) attach the _smallest_ input that reproduces the problem
>
> About ST_IsValid: lines are always valid, so there's no need to test.
> Most likely this is a robustness issue failing to deal with very close
> but not equal lines.
>
> NOTE: I've tried my reduced input (~40) geoms against the topology builder
> and it also resulted in errors, until I specified a tolerance of 1e-4.
>
> --strk;
>
>   ()   Free GIS & Flash consultant/developer
>   /\   http://strk.keybit.net/services.html
> ___
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> postgis-users@lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
>
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Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[Rémi Cura]

Hey,
I executed your data,
the following command solve the problem (with very recent GEOS for me)
(POSTGIS="2.2.0dev r12846" GEOS="3.5.0dev-CAPI-1.9.0 r0" PROJ="Rel. 4.8.0,
6 March 2012" GDAL="GDAL 2.0.0dev, released 2014/04/16" LIBXML="2.8.0"
RASTER)

:

DROP TABLE IF EXISTS unique_polygon ;
CREATE TABLE unique_polygon AS
SELECT geom_set_id,  row_number() over() as gid, ST_Translate(dmp.geom,
- 385614, - 4795454 ) AS geom
FROM error_generating_polygons,unnest(polygons) as geomn,
st_dump(geomn) as dmp;
CREATE INDEX ON unique_polygon USING GIST(geom) ;

DRoP TABLE IF EXISTS unioned_poly ;
CREATE TABLE unioned_poly AS
SELECT ST_Union( ST_MakePolygon(ST_ExteriorRing(geom)) )
FROM unique_polygon
GROUP BY geom_set_id
(150 sec)


The change compared to your approach : convert input to table of simple
polygons, (no array, no multi).
Then  translate to improve precision in geos computing

Then the union.
I don't really understand what you are trying to do,
but ist_union seems dangerous and quit ineffective  for that .

Of course reducing the number of useless points before union make it 10
times faster .

DRoP TABLE IF EXISTS unioned_poly ;
CREATE TABLE unioned_poly AS
SELECT ST_Union(
ST_Buffer(
ST_MakePolygon(
ST_ExteriorRing(
ST_SImplifyPreserveTopology(
geom
,10
)
)
)
,1 )
)
FROM unique_polygon
GROUP BY geom_set_id
(17 sec)

Cheers,
Rémi-C

2015-02-09 13:00 GMT+01:00 Rémi Cura :

> Hey Sandro,
> this is a precision related issue,
> coordinates are way too big and should be translated.
> Cheers,
> Rémi-C
>
> 2015-02-09 12:25 GMT+01:00 Sandro Santilli :
>
>> On Tue, Feb 03, 2015 at 11:28:35AM -0500, BladeOfLight16 wrote:
>>
>> >
>> https://drive.google.com/file/d/0B_6I7kRgE8teVUpha2Q4ZlNDMWs/view?usp=sharing
>> .
>>
>> ...
>>
>> > DO $$
>> > DECLARE problem_row error_generating_polygons%ROWTYPE;
>> > BEGIN
>> >   FOR problem_row IN (SELECT * FROM error_generating_polygons) LOOP
>> > BEGIN
>> >   PERFORM ST_Union(ST_Boundary(geom))
>> >   FROM UNNEST(problem_row.polygons) p (geom);
>> >   RAISE NOTICE 'geom_set_id % succeeded', problem_row.geom_set_id;
>> > EXCEPTION
>> >   WHEN OTHERS THEN
>> > RAISE NOTICE 'Error for geom_set_id % (Code %): %',
>> > problem_row.geom_set_id, SQLSTATE, SQLERRM;
>> > END;
>> >   END LOOP;
>> > END
>> > $$;
>>
>> First of all I confirm it still happens with GEOS="3.5.0dev-CAPI-1.9.0
>> r4038".
>> Second, I took a look at a random set (geom_set_id=1) and I found it
>> pretty
>> big. That's to say you could probably further reduce the dataset for the
>> ticket. That set contains 109 polygons, I can get the error by attempting
>> to union the boundaries of the first 40 in that set, and I'm sure you can
>> further reduce the input.
>>
>> So my suggestion:
>>
>>  1) file the ticket
>>  2) attach the _smallest_ input that reproduces the problem
>>
>> About ST_IsValid: lines are always valid, so there's no need to test.
>> Most likely this is a robustness issue failing to deal with very close
>> but not equal lines.
>>
>> NOTE: I've tried my reduced input (~40) geoms against the topology builder
>> and it also resulted in errors, until I specified a tolerance of 1e-4.
>>
>> --strk;
>>
>>   ()   Free GIS & Flash consultant/developer
>>   /\   http://strk.keybit.net/services.html
>> ___
>> postgis-users mailing list
>> postgis-users@lists.osgeo.org
>> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
>>
>
>
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Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[BladeOfLight16]

On Mon, Feb 9, 2015 at 6:25 AM, Sandro Santilli  wrote:

> First of all I confirm it still happens with GEOS="3.5.0dev-CAPI-1.9.0
> r4038".
> Second, I took a look at a random set (geom_set_id=1) and I found it pretty
> big. That's to say you could probably further reduce the dataset for the
> ticket. That set contains 109 polygons, I can get the error by attempting
> to union the boundaries of the first 40 in that set, and I'm sure you can
> further reduce the input.
>

Thanks for taking a look. I'll work on doing that when I can find the time,
but I don't expect that to be a fast process at all. Even just checking for
the pairwise case took a decent amount of time to develop the query and
took overnight to finish running (even with optimizations like a bounding
box intersection test). I don't really have any good heuristic that could
narrow down the possibilies for reproducing, so I don't see much option
other than to brute force it possibly with some kind of filter. That's why
I didn't put more effort into shrinking the input set to begin with.

Is a PostGIS database dump an okay format to provide the shapes, or would
you prefer something else? I suppose I could dump groups into shapefiles or
something like that if it's more convenient.

On Mon, Feb 9, 2015 at 7:00 AM, Rémi Cura  wrote:

> this is a precision related issue, coordinates are way too big and should
> be translated.
>

I understand what you mean by that (as in floating point problems due to
size), but these coordinates are pretty typical. This is a standard UTM
projection, zone 15N in middle America. It's even predefined in PostGIS'
list of spatial references. I'm told ESRI had this kind of problem years
ago, but they dealt with it as far as I know. While I would choose PostGIS
over ESRI any day, this could be viewed by my coworkers as a good argument
against using PostGIS; it represents a serious reliability concern since it
applies to a broad range of functions and 2D projections. Basically, if you
use any projection with coordinates of this size (of which there are a good
number), there seems to be no telling when any function will just blow up
in your face at random.

On Mon, Feb 9, 2015 at 7:04 AM, Rémi Cura  wrote:

> Hey,
> I executed your data,
> the following command solve the problem (with very recent GEOS for me)
> (POSTGIS="2.2.0dev r12846" GEOS="3.5.0dev-CAPI-1.9.0 r0" PROJ="Rel. 4.8.0,
> 6 March 2012" GDAL="GDAL 2.0.0dev, released 2014/04/16" LIBXML="2.8.0"
> RASTER)
>

>
[Snip]
>

>
The change compared to your approach : convert input to table of simple
> polygons, (no array, no multi).
> Then  translate to improve precision in geos computing
> Then the union.
> I don't really understand what you are trying to do,
> but ist_union seems dangerous and quit ineffective  for that .
>

I'm looking at this function call in your code: ST_Union(
ST_MakePolygon(ST_ExteriorRing(geom)) ). That call seems to remove all
holes and then create the union of all the covered areas (a single
multipolygon that covers all areas covered by the originals). That is not
what I'm trying to do; I already have an outer boundary that I could use
for that purpose.

Here's what I'm trying to do. I'm trying to create an overlay (as I said in
the first sentence of my original e-mail but didn't elaborate on), in the
sense that the term is used by these two articles:
http://boundlessgeo.com/2014/10/postgis-training-creating-overlays/ or
http://trac.osgeo.org/postgis/wiki/UsersWikiExamplesOverlayTables. What
they do is they create a sort of Venn diagram, if you will; they take all
the polygons and create a new polygon for each area with a different set of
overlappying polygons. Both of them use ST_Union in the same way I am: they
take a set of linestrings and union them to create a fully noded
linestring, and then they use this linework to create a bunch of new
polygons. I'm leveraging ST_Boundary instead of ST_ExteriorRing in my code
because I need to preserve holes, but that shouldn't change the results as
far as I know. In what way is ST_Union "dangerous" and "quite ineffective"
for the purpose of noding lingstrings? If that's true, I'm apparently not
the only one who has some misconceptions, since both these articles use it
the same way. I should also note that I don't show the whole process here;
I'm only showing the part where I'm noding the linestrings because that's
where this error occurs. Once I have the polygons, I also go back and
relate them to the attributed rows in the original tables (of which there
are several).

That said, I'm trying out the translate and cutting out multi, but I am
still using an array in my actual code for a reason. Namely, I need to be
able to do this with *different* sets of geometries. These geometries come
as the result of selecting polygons from 3 or 4 different tables, each
having completely disparate sets of attributes. So basically, I need to be
able to use an arbitrary query to get the group of polygons to be passed

Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[Rémi Cura]

Hey,
last chance for you ^^

I successfully was able to remove errors in 2 ways :
 - first your geometry array contains a lot of duplicated geometry.
( rest of this is based on geom_set_id= 1)
   I suspect you forgot a where in an inner join, or something like this.
Removing the duplicate in your data seems to solve the problem
   (removing duplicate : DISTINCT ON (geom))
   I generated each pair of geometry in this set, none gave the error
individually (which lessen the chance of a legit GEOS problem)
 - second, without removing the duplicates, a combination of tanslate and
snaptogrid(0.5) was sufficient to also remove the error.

I would recommend that you analyse a little bit your data.
For instance, simply deuplicating on geom make your data set going from
--15317 geometry in arrays to  --9934

Snapping to a 0.5 grid before deduplicating further reduce the data set to
9617 (which might indicates that somewhere in your workflow you have a
precision related issue).

I never used ARCGIS, but I can bet you that ARCGIS is not precision-safe.
The only product that is truly safe is CGAL, which comes with other type of
constraints.
You could also probably use GRASS safely if cleaning the data with v.clean
on import.

Anyway, there is no safe tool, only safe way to use it. You could very
easily create another SRS that is a translation of your original srs to
increase precision.
So you simply change your workflow to ST_Transform before computing, then
ST_Transform after computing.

Lastly, I don't see the interest of using an array of geom here because you
don't need to be able to do my_array[N] (no need to access).
So you could simply use a geometry collection, so your input is a geom, and
not a geom[].

Cheers,
Rémi-C



2015-02-18 10:39 GMT+01:00 BladeOfLight16 :

> On Mon, Feb 9, 2015 at 6:25 AM, Sandro Santilli  wrote:
>
>> First of all I confirm it still happens with GEOS="3.5.0dev-CAPI-1.9.0
>> r4038".
>> Second, I took a look at a random set (geom_set_id=1) and I found it
>> pretty
>> big. That's to say you could probably further reduce the dataset for the
>> ticket. That set contains 109 polygons, I can get the error by attempting
>> to union the boundaries of the first 40 in that set, and I'm sure you can
>> further reduce the input.
>>
>
> Thanks for taking a look. I'll work on doing that when I can find the
> time, but I don't expect that to be a fast process at all. Even just
> checking for the pairwise case took a decent amount of time to develop the
> query and took overnight to finish running (even with optimizations like a
> bounding box intersection test). I don't really have any good heuristic
> that could narrow down the possibilies for reproducing, so I don't see much
> option other than to brute force it possibly with some kind of filter.
> That's why I didn't put more effort into shrinking the input set to begin
> with.
>
> Is a PostGIS database dump an okay format to provide the shapes, or would
> you prefer something else? I suppose I could dump groups into shapefiles or
> something like that if it's more convenient.
>
> On Mon, Feb 9, 2015 at 7:00 AM, Rémi Cura  wrote:
>
>> this is a precision related issue, coordinates are way too big and should
>> be translated.
>>
>
> I understand what you mean by that (as in floating point problems due to
> size), but these coordinates are pretty typical. This is a standard UTM
> projection, zone 15N in middle America. It's even predefined in PostGIS'
> list of spatial references. I'm told ESRI had this kind of problem years
> ago, but they dealt with it as far as I know. While I would choose PostGIS
> over ESRI any day, this could be viewed by my coworkers as a good argument
> against using PostGIS; it represents a serious reliability concern since it
> applies to a broad range of functions and 2D projections. Basically, if you
> use any projection with coordinates of this size (of which there are a good
> number), there seems to be no telling when any function will just blow up
> in your face at random.
>
> On Mon, Feb 9, 2015 at 7:04 AM, Rémi Cura  wrote:
>
>> Hey,
>> I executed your data,
>> the following command solve the problem (with very recent GEOS for me)
>> (POSTGIS="2.2.0dev r12846" GEOS="3.5.0dev-CAPI-1.9.0 r0" PROJ="Rel.
>> 4.8.0, 6 March 2012" GDAL="GDAL 2.0.0dev, released 2014/04/16"
>> LIBXML="2.8.0" RASTER)
>>
>
>>
> [Snip]
>>
>
>>
> The change compared to your approach : convert input to table of simple
>> polygons, (no array, no multi).
>> Then  translate to improve precision in geos computing
>> Then the union.
>> I don't really understand what you are trying to do,
>> but ist_union seems dangerous and quit ineffective  for that .
>>
>
> I'm looking at this function call in your code: ST_Union(
> ST_MakePolygon(ST_ExteriorRing(geom)) ). That call seems to remove all
> holes and then create the union of all the covered areas (a single
> multipolygon that covers all areas covered by the originals). That is not
> what I'm tryin

Re: [postgis-users] Getting TopologyExections when trying to node linestrings to create an overlay

[Rémi Cura]

Computing finished successfuly on your data.
The change I did is :
ST_Polygonize(ST_Node(ST_Collect(geom)) )

It is awfully slow tough (1 hour for all you dataset I think)

Cheers,
Rémi-C

2015-02-18 13:07 GMT+01:00 Rémi Cura :

> Hey,
> last chance for you ^^
>
> I successfully was able to remove errors in 2 ways :
>  - first your geometry array contains a lot of duplicated geometry.
> ( rest of this is based on geom_set_id= 1)
>I suspect you forgot a where in an inner join, or something like this.
> Removing the duplicate in your data seems to solve the problem
>(removing duplicate : DISTINCT ON (geom))
>I generated each pair of geometry in this set, none gave the error
> individually (which lessen the chance of a legit GEOS problem)
>  - second, without removing the duplicates, a combination of tanslate and
> snaptogrid(0.5) was sufficient to also remove the error.
>
> I would recommend that you analyse a little bit your data.
> For instance, simply deuplicating on geom make your data set going from
> --15317 geometry in arrays to  --9934
>
> Snapping to a 0.5 grid before deduplicating further reduce the data set to
> 9617 (which might indicates that somewhere in your workflow you have a
> precision related issue).
>
> I never used ARCGIS, but I can bet you that ARCGIS is not precision-safe.
> The only product that is truly safe is CGAL, which comes with other type
> of constraints.
> You could also probably use GRASS safely if cleaning the data with v.clean
> on import.
>
> Anyway, there is no safe tool, only safe way to use it. You could very
> easily create another SRS that is a translation of your original srs to
> increase precision.
> So you simply change your workflow to ST_Transform before computing, then
> ST_Transform after computing.
>
> Lastly, I don't see the interest of using an array of geom here because
> you don't need to be able to do my_array[N] (no need to access).
> So you could simply use a geometry collection, so your input is a geom,
> and not a geom[].
>
> Cheers,
> Rémi-C
>
>
>
> 2015-02-18 10:39 GMT+01:00 BladeOfLight16 :
>
>> On Mon, Feb 9, 2015 at 6:25 AM, Sandro Santilli  wrote:
>>
>>> First of all I confirm it still happens with GEOS="3.5.0dev-CAPI-1.9.0
>>> r4038".
>>> Second, I took a look at a random set (geom_set_id=1) and I found it
>>> pretty
>>> big. That's to say you could probably further reduce the dataset for the
>>> ticket. That set contains 109 polygons, I can get the error by attempting
>>> to union the boundaries of the first 40 in that set, and I'm sure you can
>>> further reduce the input.
>>>
>>
>> Thanks for taking a look. I'll work on doing that when I can find the
>> time, but I don't expect that to be a fast process at all. Even just
>> checking for the pairwise case took a decent amount of time to develop the
>> query and took overnight to finish running (even with optimizations like a
>> bounding box intersection test). I don't really have any good heuristic
>> that could narrow down the possibilies for reproducing, so I don't see much
>> option other than to brute force it possibly with some kind of filter.
>> That's why I didn't put more effort into shrinking the input set to begin
>> with.
>>
>> Is a PostGIS database dump an okay format to provide the shapes, or would
>> you prefer something else? I suppose I could dump groups into shapefiles or
>> something like that if it's more convenient.
>>
>> On Mon, Feb 9, 2015 at 7:00 AM, Rémi Cura  wrote:
>>
>>> this is a precision related issue, coordinates are way too big and
>>> should be translated.
>>>
>>
>> I understand what you mean by that (as in floating point problems due to
>> size), but these coordinates are pretty typical. This is a standard UTM
>> projection, zone 15N in middle America. It's even predefined in PostGIS'
>> list of spatial references. I'm told ESRI had this kind of problem years
>> ago, but they dealt with it as far as I know. While I would choose PostGIS
>> over ESRI any day, this could be viewed by my coworkers as a good argument
>> against using PostGIS; it represents a serious reliability concern since it
>> applies to a broad range of functions and 2D projections. Basically, if you
>> use any projection with coordinates of this size (of which there are a good
>> number), there seems to be no telling when any function will just blow up
>> in your face at random.
>>
>> On Mon, Feb 9, 2015 at 7:04 AM, Rémi Cura  wrote:
>>
>>> Hey,
>>> I executed your data,
>>> the following command solve the problem (with very recent GEOS for me)
>>> (POSTGIS="2.2.0dev r12846" GEOS="3.5.0dev-CAPI-1.9.0 r0" PROJ="Rel.
>>> 4.8.0, 6 March 2012" GDAL="GDAL 2.0.0dev, released 2014/04/16"
>>> LIBXML="2.8.0" RASTER)
>>>
>>
>>>
>> [Snip]
>>>
>>
>>>
>> The change compared to your approach : convert input to table of simple
>>> polygons, (no array, no multi).
>>> Then  translate to improve precision in geos computing
>>> Then the union.
>>> I don't really understand what you are tryin