[mkgmap-dev] Remove short arcs

Thu Jan 17 16:23:28 GMT 2013

On 17.01.2013 16:01, Gerd Petermann wrote:
>
> reg. test data: I did not yet try to understand why a short arc brakes
> routing. I assume it is because you can't calculate the bearing with
> an appropriate precision?
> I just know that I see error messages like "road ... contains zero 
> length arc at ... "
> or "road ... contains consecutive identical nodes at ... "
> when I omit the removeShortArcs call.
> So, I'll try to run the first version of the patch against many tiles
> and see what happens. If I don't find a problem in Europe,
> it is likely that we don't need iteration.
>
> OK?
>
> Gerd
>
> >

The reason As far as I can remember is that if we have the following 
situation

    #
    #
    #
--- O UUU ---
    #
    #
    #

Now consider both # and - U and O stand for streets. O must not be 
shorter than the routing resolution (which is twice the minimal distance 
we can put points), else O will be unroutable.
I found out about it, by having a very short stretch of a road on a 
bridge, where directly after the bridge (or was is actually sharing a 
point with the bridge?) a crossing pops up. As soon as we made sure that 
O is ~5.4m the routing worked again.

Im not sure if

--- UUU --- with UUU being shorter than 5.4 works though. (UUU being e.g 
a bridge).
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