[mkgmap-dev] Remove short arcs

Thu Jan 17 22:33:38 GMT 2013

On 17/01/13 20:17, Gerd Petermann wrote:
> So, in short, I think the best solution until now is the one we have in
> r2448, and I think we
> should adapt the unit test.

OK I will commit the simple test fixes, and disable the complicated to 
fix one for now.

> I still don't understand why a short arc breaks routing, I assume this
> is caused by
> some Garmin limit.

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.

(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).

..Steve