[OSM-talk] OSM maps on Garmin GPS

[Mikel Maron]

I wasn't advocating PostGIS over MySQL spatial, or suggesting anything for the core editing database.

The essential speed up, as far as I understand, is that mapnik processes planet.osm and inserts the complete
geometry of each element into a single row, with selected tags as columns. This is in contrast to the main editing
database which requires an intensive join to get geometries and tags. In order to search on complete geometries, that
requires a geo aware database. Mapnik has an existing adaptor for PostGIS.


btw, the new tiling system still feels a bit like magic to me!

----- Original Message ----
From: Lars Aronsson <lars at aronsson.se>
To: talk at openstreetmap.org
Sent: Tuesday, November 21, 2006 12:30:43 PM
Subject: Re: [OSM-talk] OSM maps on Garmin GPS

Mikel Maron wrote:
> I can see some tie ins with the new tiling infrastructure. For 
> mapnik, queries are run against a PostGIS database (populated 
> from planet.osm) which is part of the reason why it's so fast.

You make it sound like magic.  What is the essential algorithm or 
data structure in PostGIS that causes this speed-up?  Could the 
same speed be achived with the GIS extensions to MySQL?  Could it 
be achieved by changing the old OSM tile generation code on top of 
the regular MySQL?


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se

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