[OSM-dev] Best way to select from a region

Frederik Ramm frederik at remote.org
Tue Sep 1 02:12:10 BST 2009


Hi,

Stephan Knauss wrote:
> I'm trying to create lists of features inside a specific country.
> What would be the most convenient way to do this?

There is no convenient way I know of ;-)

> As source I could either use a planet file and use a SAX parser or 
> PostgreSQL with the osm2pgsql mapnik schema.

I suggest using osmosis with the --bp option.

> As a boundary polygon I would prefer the borders already in the database 
> as these are more accurate compared to the polygon files of cloudmade.

In 95% of cases you will find that the borders in the database are 
unsuitable because they do not form a proper closed polygon. Plus, 
PostGIS definitely sucks at point-in-polygon performance, especially if 
your polygon has 30k points.

I suggest that you use Gary68's polygon tool (perl script in SVN) to 
derive .poly files from a suitable OSM exctract (or use .poly files that 
are already in SVN). Then simplify these files with the simplify-poly 
script also in SVN unless you really, really want super-exact and 
super-slow cutting. Then use Osmosis to cut out an area. Pay attention 
to the various options (idTrackerType, clipIncompleteEntities, 
completeWays, completeRelations - the latter two being perfect ways to 
keep your server busy for a few days if you work with the full planet file).

Bye
Frederik




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