mkgmap has a LineMergeFilter but that does not merge the road network.

Attached patch performs a merging in the OSM data just before the road network is created. This has the advantage that the source code for the merging is quite easy. Turn restrictions and through routes are considered.

I tested some data in germany and got a reduction of 5% to 12% (number of roads). I did not find any improvements but also no downgrades in routing. But I did not test long distance routing (> 600km).

I think the merge results can be improved if the access handling and some other parts are moved from source code to the style files. This makes it easier for the merger to say that two roads have the same attributes and can be merged without problems. But that's a task for the future...

I have already uploaded a compiled version: http://files.mkgmap.org.uk/detail/148

For anyone who is interested in the code: Please check the tag list (variable flatCompareTags) in the new RoadMerger. This taglist gives all tags that must be equal so that two roads can be merged. Is this list complete? Can I remove some tags from it?

Have fun!
WanMil

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-- 
keep on biking and discovering new trails

Felix
openmtbmap.org & www.velomap.org