[mkgmap-dev] (almost) duplicated node issue

Mon May 25 20:41:37 BST 2009

Well, when a node is duplicated (I think, latitudes and longitudes matches up to the last digit), JOSM validator detects it as a map error and offers the possibility to automatically correct the issue.

I think there are two cases:

(1) the 2 duplicated nodes are not connected by any arc. Well, if JOSM collapses the two nodes in one, it connects each other arcs that weren't connected before.

(2) the 2 duplicated nodes are connected by an arc (a zero length arc). Well, if JOSM collapses the two nodes in one, I guess it just deletes the zero length arc. But if the deleted arc was one way, the deletion makes possible routes that weren't possible before

I want to say: duplicated nodes and almost duplicated nodes are map errors (expecially if they describe an highway). We do not know wich was the right intention of the mapper (make routing possible/impossible).

I think that the best we can do when mkgmap finds 2 nodes that encode in the same IMG point (so in both cases: duplicated nodes or almost-duplicated nodes) is to collapse the 2 nodes in one node exacly as JOSM validator would do if they were duplicated.

Does it sound good?

Just my proposal...

--- Lun 25/5/09, Mark Burton <markb at ordern.com> ha scritto:

> Da: Mark Burton <markb at ordern.com>
> Oggetto: Re: R: [mkgmap-dev] (almost) duplicated node issue
> A: mkgmap-dev at lists.mkgmap.org.uk
> Data: Lunedì 25 maggio 2009, 16:26
> 
> Hi Johann,
> 
> > Would it be an idea to enter a slightly longer
> distance for the arc in 
> > the routing db?
> 
> I tried that, it didn't help.
> 
> > I really dont like such things, as they are only are
> just workarounds, 
> > but it seems the easiest solution until the correct
> encoding is known.
> 
> I don't think the issue is the correctness of the encoding,
> it's more
> to do with the fact that the OSM map can contain nodes that
> are closer
> together than the Garmin can accept. The thorny issue is
> how to munge
> the data so that the GPS (or mapsource) doesn't barf but
> the map is
> still usable (connections not broken, etc.)
> 
> One trivial fix is to delete any way that would otherwise
> cause a
> problem. That should stop the garminware from barfing but
> would not be
> ideal from the user's point of view because it would break
> the routing.
> 
> Cheers,
> 
> Mark
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