[mkgmap-dev] Strange long distance routes on Nüvi

Sun Jul 30 12:59:28 BST 2017

Hi Bodo,

I think Garmin is using some kind of hierarchical routing algorithm. It 
looks like GPS uses only class 4 and 3 roads for long distances (at 
least in case of recent nuvis, hiking GPS can be more flexible). For 
proper routing GPS needs a continuous and reasonably dense notwork of 
high class roads.

My patch address 2 problems in default style.

First are links and roundabouts, which often get lower road class than 
connected roads. This breaks continuity of high class network and breaks 
routing. My patch simply increases road class for many links and 
roundabout types.

Second problem is low density of good highways in some regions. To make 
it better, my patch increases road class for international roads. These 
roads are detected by "ref" and "int_ref" tags, both in objects and 
relations.

I have added some small general corrections for 
"highway=mini_roundabout", "access=hov" and "oneway=reversible".

There is no direct change for "inc\roadspeed". Maybe patch overrides 
some of your changes in "lines" file? Anyway, I don't think road speed 
breaks routing, you can tune it to your liking.

-- 
Best regards,
Andrzej