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[mkgmap-dev] Commit: r1377: Limit length of lines to work around problems when subdividing long lines.

From Felix Hartmann extremecarver at googlemail.com on Thu Nov 12 13:40:53 GMT 2009

Mark Burton wrote:
> Hi Felix,
>> I am not sure which of todays changes is responsible, but routing in 
>> Mapsource became a lot worse! Often I get routes 10-30% longer or on 
>> less priorised ways than before, this is a drastic example but happens 
>> on every 10 route:
>> Yellow route is old SVN 1773, pink is newest SVN version (yellow is 
>> 17.8km and 33 minutes, pink is 26.5km and 56 minutes):
> Please try increasing the values of MAX_ARC_LENGTH and MAX_LINE_LENGTH
> and see if that improves things. I would not expect MAX_LINE_LENGTH to
> make a difference as that only influences lines not routable ways.
> If the reduction in MAX_ARC_LENGTH is causing your routing to become
> worse, that's going to conflict with the issue Marko reported.

Could it be that at resolution 24 we have filters running for smoothing 
lines that cause the problem, or the tweeze arc causing problems with 
low values?

The crazy thing is that if I increase max_arc_length at resolution=24 I 
will even see roads with different shapes/angles at the junction.

The thing is that with more max_arc_length and max_line_length (both set 
to 80.000) even on very short roads routing get better - roads that 
definitely don't have more than 20 points or longer than 200-300m.
This however happens only once the overall length of the route without 
via points gets longer (starting at about 30-40km).

Another thing we could try is to make the tweeze arc filter much more 
radical - maybe this would help in the routing problem. I still cannot 
believe that the max_arc_length itself is responsible for the problems 
on the Nuvi.
> Cheers,
> Mark
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