Johann Gail wrote:
I noticed that some Garmin maps display 1:1 to openstreetmap data, but on route calculation show up to 10% shorter distance. Maybe here only routing nodes are simplifed (straighter line).
Sorry, could you explain in more detail? I'm not sure what you mean here. 'Simplifiing routing nodes' is the thing, which tries Mark with his bogus node patch.
Well I noticed this on a serpentine way in the Swiss Alps.
I routed over Topo Swiss v2 and distance was 2.3km, then on Openstreetmap mkgmap created map 2.8km. Though when putting the maps transparent above each other, there was nearly no difference to tell in the shape of the ways. From plain eye openstreetmap seemed to be shorter even. Therefore I assumed that the way it was showing was longer than the way the routing happened on. Also my bicycle computer showed 3.1km on the supposedly 2.3km part of the route. .
Thats interesting. The distance for routing is contained in the routing tables and these are not touched from me in any patch. I really don't know, as I have never looked into it, but here is an assumption: I think the arcs conains the distnace from node to node. Maybe here is the direct line from node to node calculated and not the real length from the winding serpentine.
I do know that we have not touched this, but Garmin seems to have done so in the Topo Swiss v2 which they sell. (as all Swiss Maps really expensive). It is for me from the information inside the best map by Garmin, however Autorouting is crap, just like on any outdoor garmin map. Only exception being the onroute maps (but their principle will not work outside of Holland IMHO - where cyclerouting works well because there is an abundance of cycleways.) - I have heard however that Onroute will publish a European wide cycle map for Garmin GPS next spring.
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