[postgis-users] postgis topology strange behavior

[Gonçalo Revez]

Hi, answers below:

On Mon, Feb 24, 2014 at 1:53 PM, Sandro Santilli <strk at keybit.net> wrote:

> On Mon, Feb 24, 2014 at 12:01:28PM +0000, Gonçalo Revez wrote:
> > Hello,
> >
> > I'm using the postgis topology with the following example below.
> >
> > It inserts three contiguous polygons, but the third has a strange
> behavior.
> >
> > It seems that the polygon doesn't snap totally to the other polygon (with
> > model tolerance of 0.1), where he should split the edges and create a
> node.
> >
> > The problem raises two edges "overlapped". (I attach an image showing the
> > topology error).
>
> Does ValidateTopology catches that error ?
>

*G: No the validation doesn't catch any error.*

>
> > In fact, using the jts viewer, the third polygon overlaps the first
> > polygon, but below the topology model tolerance.
>
> In the topology primitives tables there are no polygons, the errors
> you're after are overlapping or crossing edges, can you find them ?
>

*G: yes, the edges, 2 and 6,  are overlapped (or seems to).*
*I attach two image with edge2 identified and edge6 identified (where they
share some part)*

*Shouldn't be create an edge between the part both edges share (and created
a node) ?*

*For example, if I override the tolerance value of the model through **the
function toTopoGeom of the insert of the polygon 3, *
*with a value around 4 meter, I get the expected. The edges are splitted.*

*But the edges doesn't distance more than 1 meter.*


> > How is it possible to solve this type of situation or what could be the
> > error in example?
>
> Can it be you're referring to TopoGeometry overlap ?
> Those ones are not errors, but perfectly leagal situations.
> You can find them by counting the number of TopoGeometry objects
> each topolgy face primitive contributes to.
> Faces with count > 1 are overlaps, faces with count < 1 are "gaps".
>

*G: I have 3 polygons, 3 topoGeometry and 3 faces (and face 0). It didn't
create gaps.*

*If i tried to insert the third polygon again, meaning, duplicate the
topogeometry table record, and then using the same faceid , i get *

*the error: geometry intersects edge 6*

*Thanks*



> --strk;
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