[postgis-users] Problems with GeomUnion

[Bill Binko]

On Fri, 8 Apr 2005, Martin Davis wrote:

> In JTS buffer is pretty tolerant of invalid topology.  That's why I
> suggested using it to clean up bad geometry.  AFAIK it should have
> similar behaviour under GEOS.  It's not 100% guaranteed to work,
> however, so if there are failures some other approach might be needed
> for them.
> 
> Fixing topology errors is usually not a simple single-step process - it
> can require some deviousness to deal with the infinite number of ways
> that geometry can be bad.
> 

I'm learning that :(

One thing that would really help would be if there was a way to get 
isvalid() to return why the geometry is invalid.  It looks like the ones 
that get a NOTICE: Self-Intersection can be fixed with buffer(), but those 
that say things like:

NOTICE:  IllegalArgumentException: points must form a closed linestring
NOTICE:  IllegalArgumentException: points must form a closed linestring
NOTICE:  IllegalArgumentException: geometries must not contain null elements

make buffer do ugly things.

I think the number of those is about 5% of my failures.  I'd rather handle 
those :)

I think I might be able to marry up stderr and stdout and get a list... 
we'll see.

Bill