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.