[mkgmap-dev] Thoughts on OSM routing

Tue Feb 17 14:00:24 GMT 2009

Hi Toby,

> As I said, bad source data is more of an issue - I'm cleaning up quite
> a bit as I go.

Good!

> One thing that caught me by surprise was approaching a roundabout and
> just being told to keep left - it wasn't until I reached the splitter
> island that I got given the roundabout exit to take.  I guess this is
> the opposite of the missing-exits problem, in that the island was
> large enough to count as a separate road for the eTrex's purposes.

Did it think that the splitter was, itself, a left turn?

> One thing I do have a concern about is mixing speed rules into the lines
> file - I've patched my style as instructed, but now all roundabouts are
> drawn the same, because there's a rule for roundabouts for speed purposes.

Not sure I understand that. The default rules now look like this:

junction=roundabout & highway=trunk [0x0c road_class=3 road_speed=5 resolution 16]
junction=roundabout & highway=primary [0x0c road_class=3 road_speed=4 resolution 19]
junction=roundabout & highway=secondary [0x0c road_class=2 road_speed=3 resolution 20]
junction=roundabout & highway=tertiary [0x0c road_class=1 road_speed=3 resolution 20]
junction=roundabout & highway=unclassified [0x0c road_class=1 road_speed=2 resolution 21]
junction=roundabout [0x0c road_class=0 road_speed=1 resolution 21]

> (I'm too lazy to introduce roundabout rules for each highway class).  I
> think that this probably needs a re-think, because it would be nice to
> combine information to give a better resultant speed guess (including
> features such as traffic signals, number of lanes, etc - and for roads in
> "place=*" as described[1] on the OSM wiki).
> 
> [1] <URL: http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Maxspeed >

The maxspeed tag should be effective as support for that was recently added
by Bernhard.

Cheers,

Mark