[OSM-talk] Where came the concept of ways, segments, nodes?
artem at mapnik.org
Wed Mar 21 10:35:19 GMT 2007
On 21 Mar 2007, at 09:54, Martijn van Oosterhout wrote:
> On 3/21/07, Mike Collinson <mike at ayeltd.biz> wrote:
>> May I ask some of our more long standing members where the concept
>> OSM ways, segments, nodes came from?
> I don't know exactly (I wasn't there) but I think it came from looking
> at existing datasets which mostly work on the basis of polylines. A
> line consisting of multiple points. Now, that's terribly inefficient,
> so you seperate out the duplication and you get what we have now.
Perhaps, it came from a topological model - node, link , face ?
Do you mean inefficient for storing data? Can you explain more?
> In the process one inefficiency snuck in, namely that ways don't
> represent contiguous lines (they don't map exactly to polylines). Of
> we could enforce that in the API then we'd be set. The mapnik
> converter would probably like that :)
If you're talking about osm2pgsql converter it's doesn't matter.
osm2pgsql creates planar graph for every bunch of nodes that are part
of a way and creates *clean* geometries (as defined in Simple
Features for SQL). It would be nice to avoid this step but this would
require changing data model.
> Have a nice day,
> Martijn van Oosterhout <kleptog at gmail.com> http://svana.org/kleptog/
> talk mailing list
> talk at openstreetmap.org
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