[mkgmap-dev] Thoughts on OSM routing

Tue Feb 17 14:27:47 GMT 2009

0> In article <20090217140024.4c823ae4 at crow>,
0> Mark Burton <URL:mailto:markb at ordern.com> ("Mark") wrote:

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

No, the instruction was something like "keep left, 200m".  It's just
that not having had routable maps before (unless you count the basemap),
I was just slightly surprised (I'd seen the sign for the roundabout, and
was expecting a roundabout instruction).  I'm over it now.

>> 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.

Mark> Not sure I understand that. The default rules now look like this:
Mark>
Mark> junction=roundabout & highway=trunk [0x0c road_class=3 road_speed=5 resolution 16]
Mark> junction=roundabout & highway=primary [0x0c road_class=3 road_speed=4 resolution 19]
Mark> junction=roundabout & highway=secondary [0x0c road_class=2 road_speed=3 resolution 20]
Mark> junction=roundabout & highway=tertiary [0x0c road_class=1 road_speed=3 resolution 20]
Mark> junction=roundabout & highway=unclassified [0x0c road_class=1 road_speed=2 resolution 21]
Mark> junction=roundabout [0x0c road_class=0 road_speed=1 resolution 21]

You're right - my niggle was that they all map to 0x0c, and thus
appear in different colour to the roads they are part of.  Can I
just change them to match the highway=* rules?

[/me looks at garmin_feature_list.csv] I guess not - presumably this
is what the device uses to know it's a roundabout rather than a random
one-way road that just happens to be circular.  Never mind.

>> 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 >

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

Trouble is that maxspeed refers to the legal maximum; near here there's
a 30mph-limit road with about 10 sets of lights in half a mile and the
effective speed is about 10mph (slightly faster on a bike).  Maybe it's
time to resurrect a proposal for a more realistic speed tag on ways...