[OSM-talk] Segments, ways and order

Frederik Ramm frederik at remote.org
Tue Jul 31 21:46:01 BST 2007


> Every week, an export, an import, and so on... again, with a gis model, we can 
> use mapnik in near-real time.

There are people working on porting the API to PostGIS. Once that's 
done, extensive performance checks can be carried out.

However, unless you're using Oracle which has GIS and topology support, 
we will always have to store everything twice - once as pretty 
"linestrings" or whatever, and a second time as the graph it really is.

PostGIS linestrings by themselves don't give us topology - they will 
happily store two streets as individual linestrings and will *not* be 
able to tell you whether the point where they both meet is actually a 
junction or whether it's just two features incidentally meeting there. 
That's fine for read-only "shapefile" type access, but unusable for 
routing and editing. So we still need the topological information.

As far as I understand, the current idea is to somehow use triggers etc. 
to keep a "shadow world" of GIS objects in sync with our existing data 
model, so that you can use fast bounding box queries etc. on the GIS 
objects but, through back references, still return the proper nodes and 
ways like we're used to.

I'm not involved in this effort, just repeating what has been written on 
this list in the past.


Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'

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