[gdal-dev] Simplify a polygon topology doesn't preserve the topology

[pcreso at pcreso.com]

Does Postgis ST_SimplifyPreserveTopology() work for you?

http://postgis.org/docs/ST_SimplifyPreserveTopology.html

Cheers,

  Brent Wood



--- On Tue, 2/21/12, Arnd Wippermann <arnd.wippermann at web.de> wrote:

From: Arnd Wippermann <arnd.wippermann at web.de>
Subject: [gdal-dev] Simplify a polygon topology doesn't preserve the topology
To: gdal-dev at lists.osgeo.org
Date: Tuesday, February 21, 2012, 10:36 AM

Hi,

I try to simplify a polygon topology (GDAL 1.9.0, released 2011/12/29).


SET INPUT="top1_bene.gml"

SET OUTPUT_01="top1_bene_sim_01.gml"
SET OUTPUT_005="top1_bene_sim_005.gml"
SET OUTPUT_001="top1_bene_sim_001.gml"

"%prgpfad%\ogr2ogr" -f "GML" %OUTPUT_01%  %INPUT% -simplify 0.1
"%prgpfad%\ogr2ogr" -f "GML" %OUTPUT_005% %INPUT% -simplify 0.05
"%prgpfad%\ogr2ogr" -f "GML" %OUTPUT_001% %INPUT% -simplify 0.01


but preserving the topology doesn't work for tolerances above a treshold.

I get a correct result for a tolerance of 0.01, but for 0.05 and 0.1
the results are only in parts correct.

see:
http://gis.ibbeck.de/OLClient/OLClient.asp?WMC=/ginfo/tests/ogr/simplify/Sim
plify_bene_ogr.wmc.xml

I have it also tried with a polygon topology of the us states and the result
wasn't great.

(I get similar results using postGis ST_Simplify.)

Apart the tolerance are there other options to consider or is it a bug?

The polygon topology consists of two polygons and the shared border have
identical vertices.

Arnd

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