[postgis-users] Problem (bug?) in ST_POLYGONIZE

[Andreas Neumann]

Indeed - this ST_SnapToGrid() does the trick - and explains why
ST_Polygonize failed. I wonder if there is a way to see these very slight
inaccuracies with "ST_AsText()". In my case ST_AsText() only returned
three digits after the comma (that's why I assumed the start/end points
are actually the same), not the 10 digits you mention below. Is there any
trick to tell ST_AsText() to be more accurate?

Thanks again,
Andreas

> This is not a bug. It looks like your linestrings are not properly noded.
>
> IE. on your line in question, the end node is POINT (697787.741
> 247263.451), but the other two lines are noded at POINT
> (697787.7410000002 247263.451).
>
> Try using snaptogrid().
>
> SELECT geom AS the_geom
> FROM ST_Dump((
>    SELECT ST_Polygonize(ST_SnapToGrid(the_geom, 0.001)) AS geom
>    FROM admin.plz));
>
> Cheers,
>
> -------------
> Kevin Neufeld
> Software Developer
> Refractions Research Inc.
> 300-1207 Douglas St.
> Victoria, B.C., V8W 2E7
>
> Phone: (250) 383-3022
> Email: kneufeld at refractions.net
>
>
>
> Andreas Neumann wrote:
>> Hello,
>>
>> I have a linenetwork with 15 LINESTRING() elements. I am using
>> ST_POLYGONIZE() to create new POLYGON() elements. I'd expect to get 6
>> polygons, but ST_POLYGONIZE() creates only 5 polygons. To make sure that
>> my data is ok, I selected all start and endpoints of the LINESTRING()s
>> and
>> made sure that every start/endpoint of a LINESTRING() has two
>> counterparts, which is the case.
>>
>> This looks like a bug to me. I would appreciate if someone else could a
>> look at my data. Attached is the dump of the table and a screenshot of
>> the
>> line-network. If you load the dump, you might want to replace the owners
>> with your own userid. In the screenshot, one line is marked as green.
>> This
>> is the line that is ignored by the ST_Polygonize() command.
>>
>> I used
>> SELECT geom AS the_geom FROM ST_Dump((SELECT ST_Polygonize(the_geom) AS
>> geom FROM admin.plz));
>> as the SQL query.
>>
>> I'd appreciate any help on my problem, resp. an answer if this might be
>> a
>> bug or not.
>>
>> Thank you,
>> Andreas
>>
>>
>>
>> ------------------------------------------------------------------------
>>
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at postgis.refractions.net
>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>


-- 
Andreas Neumann
Böschacherstrasse 6, CH-8624 Grüt/Gossau, Switzerland
Email: a.neumann at carto.net, Web:
* http://www.carto.net/ (Carto and SVG resources)
* http://www.carto.net/neumann/ (personal page)
* http://www.svgopen.org/ (SVG Open Conference)
* http://www.geofoto.ch/ (Georeferenced Photos of Switzerland)