[postgis-users] Preparing for Topology - St_CreateTopoGeo

[Chris English]

On error, a problematic point is indicated, but it refers to the indexbeing developed by splitting and doesn't refer to the original, offending row oidof the source file being processed to help tracing.  
Sometimes a geom or geom range is returned that I tried to use previously to focus in on the possible problem, unsuccessfully thus far.
Attached a file which may or may not be of interest, two smallishshape files that successfully became topologies independently,but failed when I attempted to combine them.  One multi-ploygon,one linestring.  
A log of my approach is included, which is probably the source oferror.
I will address myself to noding and St_<functions, with tolerances>to see if I can clean better before topology.
Chris

> Date: Thu, 8 Dec 2011 09:17:53 +0100
> From: strk at keybit.net
> To: postgis-users at postgis.refractions.net
> Subject: Re: [postgis-users] Preparing for Topology - St_CreateTopoGeo
> 
> On Tue, Dec 06, 2011 at 08:33:53PM -0500, Chris English wrote:
> > 
> > In your experience, it there a method to predict where failuremight
> > occur, or some characteristics of offending geometries...
> 
> Lines which are almost coincident but not quite.
> 
> > I was just wondering if through the multitudinous process of st_split,
> > addface, addedgemodface,if a progression of small remainders from the
> > splitting (or others) get carried forwardthat would fault st_createtopogeo
> > as it gets around to updating {left,right}_face fields and the like.
> 
> The function performs noding as first thing so maybe you could do the
> noding yourself on the whole data and see if it still creates problems.
> If it does you could then select only the (noded) edges that intersect
> a small buffer around the reported problematic point (was such problematic
> point reported ?).
> 
> --strk;
> 
>   ,------o-. 
>   |   __/  |    Thank you for PostGIS-2.0 Topology !
>   |  / 2.0 |    http://www.pledgebank.com/postgistopology
>   `-o------'
> 
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