[OSM-talk] conclusions from my postgres / postgis experiments
Richard Fairhurst
richard at systemeD.net
Thu Nov 23 14:02:48 GMT 2006
raphael Jacquot <sxpert at sxpert.org> wrote:
> all those people use a standard format to 'share' their data, GDF
> (Geographic Data File), which was specified by the CEN technical
> committee 278 Road Transport and Traffic Telematics which defines such
> a structure.
Sure, but they don't use that standard internally. When you buy a
satnav box for £199/300eur, it doesn't have a full GDF-format dump
inside it. The TeleAtlas data, shipped as GDF, has been processed by
TomTom/whoever into a lean, fast database. On the URL you cite:
"A GDF database (in the exchange format) will never be used as
such. Users will first transform it into their system, which
could be a GIS (Geographic Information System), car navigation
system, or routing algorithm. Therefore you cannot talk about a
GDF application, but rather an application that uses GDF.
"GDF is not a CD standard for car navigation systems. GDF is
used and converted onto the CD-ROM in the internal format of
the navigation system."
The geodata actually exists in four separate formats:
1. Original Ordnance Survey MasterMap data (for UK)
-> aggregated as part of
2. TeleAtlas master database
-> distributed to
3. TomTom plc as GDF file
-> interpreted into
4. TomTom satnav unit internal format
The master OSM database is closest to 1, maybe 2.
If I read your Grenoble example correctly, you were saying that OSM
should use a particular format (superways) because it would be more
efficient for route-planning apps, like satnavs (4). I think the
existence of GDF, rather, proves that the storage data format, 1 (=OSM
db) is different to the client data format, 4 (=routeplanner internal
format), and that the ingenious halfway house of GDF, 3, has been
devised to ease the transfer of one into another. Maybe one day we'll
have planetosm_to_gdf.pl?
cheers
Richard
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