[mkgmap-dev] Remove short arcs

Fri Jan 18 08:09:00 GMT 2013

Hi Steve,
> We know that short arc are problematic, but not exactly why. There are a
> few possibilities.
> 
> 1. The routing arcs have a length field, when the arc length is less 
> than 4.9m (in our implementation) this is stored as 0. Perhaps zero is
> bad and using 1 instead would work.
> 
> 2. Perhaps the nodes must have different Garmin coordinates. This would 
> imply a minimum separation of 2.3 (or less depending on direction and
> latitude).
> 
> 3. I believe that boundary nodes between two maps are considered 
> connected if they are up to 2 (or 3, I forget) garmin units apart.
> Perhaps this is true in general and routing will jump to unconnected 
> roads if nodes on nearby roads are too close.

A lot of maybes :-(
I have one more: I think Garmin also changes the algorithmn with new firmware
(one version broke routing completely on my Oregon 450t, don't remember exactly
which one it was)

> 
> (I thought of that last in relation to removeShortArcs removing complete 
> ways - how did no one notice? Well perhaps because very small gaps can 
> be jumped).

The small way is removed, but the gpx device will probably still route
you through it (if my last description of the algo is correct)
I am more concerned that it may remove a way with highway=steps 
and connect the nodes of two big street directly instead.

Gerd

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