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[mkgmap-dev] Problem with --adjust-turn-headings

From Apollinaris Schoell aschoell at gmail.com on Mon Feb 8 22:06:09 GMT 2010

Hi Mark,

will update the img files first to make sure osm data and img are in sync
and report back what I see.
In the past I have seen also the other case where no turn instruction was
given but I would expect one. But can't remember where. Will watch for it
more in future and take notes.

thanks for the great work, it's getting better and better!

On Mon, Feb 8, 2010 at 1:20 PM, Mark Burton <markb at ordern.com> wrote:

> Hi Apollinaris,
> > Hi Mark,
> >
> > I think I have an example where this is useful. On a ~200km drive I got
> one
> > keep left announcement where there was only a normal exit from the
> motorway.
> >
> > Before blindly adding this relation  I want to understand how the current
> > algorithm should work. maybe I should fix the osm data first
> > you mention mkgmap looks at ways, ref, names. can you explain how it's
> done?
> Sure. What it does is at each junction, it tries to determine what is
> the "main road" and what is the "side road". If it can determine that,
> it then adjusts the angle at which the side road leaves the main road
> such that it reduces the likelyhood of getting keep left/right
> instructions when you are staying on the main road and increases the
> likelyhood of getting turn left/right instructions when you want to
> take the side road.
> To determine which arcs make up the main road, it looks at some
> attributes of the routing arcs that enter and leave that node. If two
> arcs have the same ref, it's considered a strong indication that they
> make up a pair, likewise, matching names are considered good.
> The through_route relation is there to help the situation where it's
> not possible to determine from the names/refs of the roads which is the
> main road.
> Before you change any data, could you please post the OSM URL of the
> exit so that I can look at it and see if I can tell why you got a "keep
> left". I am guessing, but I wouldn't be surprised if the exit ramp was
> tagged as a road (motorway, trunk, etc.) and not as a ramp.
> >
> > btw it's much better than my old tomtom which announces keep left on too
> > many exits.
> Good!
> Cheers,
> Mark
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