[OSM-dev] Topologicial correctness in OSM

Jon Burgess jburgess777 at googlemail.com
Wed Jan 17 18:53:52 GMT 2007


On Wed, 2007-01-17 at 17:19 +0000, Nick Black wrote:
> Hello,
> 
> Whilst trying to produce .osm from the brazillian TABs, I've run into
> a problem, in that the output I can produce output in OSM XML, but it
> is topologically incorrect, as it duplicates nodes at intersections.
> My process is:
> 
> TAB > Import to PostGIS usign ogr2ogr > Script to talk to PG, and
> input data to OSM MYSQL via dao.rb .
> 
> One solution to the problem is to go through mysql and compare each
> lat and lon value to each other, identifying the duplicate nodes and
> then deleting one set and correcting their parent segment - this seems
> a rediculous way to do it though.

> Does anyone have a better idea how to go about it?  I cant see how
> PostGIS maintains topology, but it obviously does somehow.
> 

It is fairly ridiculous but works. If you can get the data into an OSM
style XML file then the script in utils/simplify/simplify.pl will do
this for you. Specify a fairly small minimum feature size e.g.
--simplify=0.00001 which should get rid of any nodes within about 1m of
each other. 

The script is quite memory hungry on larger data sets. If this is an
issue then I may be able to provide a C implementation at some time in
the future.

	Jon









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