[OSM-talk] Topology (was: OSM the mediocre alternative)

[Andy Robinson]

Artem Pavlenko wrote: 
>Sent: 26 April 2007 4:48 PM
>To: Martijn van Oosterhout
>Cc: OSM
>Subject: Re: [OSM-talk] Topology (was: OSM the mediocre alternative)
>
>
>On 26 Apr 2007, at 16:27, Martijn van Oosterhout wrote:
>
>
>	On 4/26/07, Artem Pavlenko <artem at mapnik.org> wrote:
>
>		OK, I was hoping you have something to play with. I think
>investigating
>		PostGIS topology or even fixing MySQL is a good plan. I'm
not
>so sure about
>		Oracle.
>
>
>	Is there a particular reason why we need PostGIS topology?
>
>
>
>Collecting and storing topological structure would be very useful. But, do
>we need PostGIS topology?  I'm not sure.
>
>
>
>	If we store
>	ways as arrays of node IDs and index them (which can be done in
>	standard postgres) you get almost all the way. Add a trigger to
>	automatically regenerate the polyline wherever the array changes and
>	it should work just fine.
>
>
>I don't believe that storing every single node as a separate record(object)
>would be a good idea. Some geometries can have lots of vertices and
>gathering them by id won't efficient. Only 'interesting' nodes e.g
>intersections need to be stored, IMHO.
>

Well, some nodes which might appear to be uninteresting (ie they simply
define the geometry of the way) actually carry interesting tags. However,
I've no idea whether the tag data on an object affects this discussion or
not :-)

Cheers

Andy 

Andy Robinson
Andy_J_Robinson at blueyonder.co.uk

>Cheers,
>
>
>
>	Have a nice day,
>	--
>	Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/
>
>
>
>Artem Pavlenko
>http://mapnik.org
>
>