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[mkgmap-dev] Simplifying ways

From Johann Gail johann.gail at gmx.de on Sat Nov 28 23:06:53 GMT 2009

> I actually think that one should even thing about simplifying routable 
> ways at resolution=24. Especially those that directly originate from 
> GPS tracks (that will be difficult to find out though), maybe only if 
> nodes are closer than 20m over longer distances. So say 6 nodes in 60m 
> okay, 20 nodes over 200m simplify because it seems to originate 
> directly from a track. Often people put nodes on curves very close to 
> each other,

Yes, I know such ways. You could see at a glance, that this ways are 
directly converted from gps tracks. This would be well handled be the dp 
filter. But as Mark has explained very well, at the lowest level is a 
one to one linking with rounting data. In the very first playings with 
the dp filter I enabled it in resolution 24 too, but destroyed routing 
completely. I think it is not immposible, but a very complex task to do. 
The routing tables would have to be modified afterwards. Out of scope at 
the moment, sorry. :-)
> I think one would have to experiment whether routing works better if 
> those nodes are simplified (maybe only for routing, but not for 
> display?).
The dp improves only displaying. Full stop. At least it is supposed to 
do. :-)
Its nice, if you tells me it improves routing too. But I dont understand 
how it happens. Maybe it is a side effect of the smaller drwaing data, 
leaving more space for routing data, so that less routing centers are 
needed? I really don't know.

> 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.

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