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[mkgmap-dev] Simplifying ways

From Felix Hartmann extremecarver at googlemail.com on Sat Nov 28 23:32:47 GMT 2009

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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