[OSM-dev] Feature locator powered by main OSM database?

Christopher Schmidt crschmidt at metacarta.com
Tue May 22 00:37:40 BST 2007


On Mon, May 21, 2007 at 06:32:18PM +0100, Nick Whitelegg wrote:
> Hello everyone,
> 
> I forget - did anyone ever write a feature locator powered off the main 
> OSM database?
> e.g. give me all pubs within 1 mile of 50.9, -1.4.

If you're looking at doing a search for point features based on tag
values, I think you'll find it difficult to do in a reasonable amount of
time: due to the storage of the tags as delimited text data (at least,
according to
http://svn.openstreetmap.org/sites/rails_port/db/create_database.sql),
it seems like any such query would require a sequential scan over the
entire table. It's possible that a full text index with a 'LIKE' query
could help this, but I've never seen terribly impressive performance
under this type of index. It's possible that things have improved, or
that i'm making a mistake and this is not really true anymore, but it
seems like it might be difficult to do this on a live system.  

> The nearest thing seems to be Nick Burch's "Where am I?" but that's based 
> off planet.osm, not the live database.

There's a reason for that :)

Regards,
-- 
Christopher Schmidt
MetaCarta




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