[mkgmap-dev] Turn instructions

Tue Mar 10 18:27:00 GMT 2009

On Tue, Mar 10, 2009 at 1:39 PM, Ralf Kleineisel <ralf at kleineisel.de> wrote:
> Clinton Gladstone wrote:
>
>> 0x09 and 0x08 are types for ramps. I believe this was discusse earlier
>> in this list.
>
> Do the Garmin line types influence the display only or the routing as well?
> I had thought that for routing there is the "road_class".

As far as I know (and I don't know much about the Garmin routing
algorithm), class and speed are indeed the main determiners for the
path chosen. The types (0x09 and 0x08) do carry semantic meaning, and
therefore influence display as well as the description of the route.

I have noted the following:

- Before I changed the *_link rules to 0x09 and 0x08, my device did
not give as precise a description of the exit. The exits were not
described as "ramps" in the description.

- Also, from my observations, having two tags assigned to the same
Garmin code, but with different resolutions does not seem to work. In
your example, you have [0x01 ... level 6] and  [0x01 ... level 4]
assigned to motorway and motorway_link respectively. If my
observations are correct, motorway and motorway_link will always be
displayed at the same level (either both 6 or 4 but not one or the
other). You can test this.

- I also suspect that the above may influence routing. This is much
harder to test, but I believe I noticed something similar: when I
changed primary to 0x03 from 0x02 (0x02 was also assigned to trunk),
it seemed that the routing changed to favour trunk over primary. I
have only anecdotal evidence for this.

I imagine in your case that having 0x01 assigned to both motorways and
_links will make almost no difference to the routing: the links are
almost always so short as to be negligible. You may get better route
and turn descriptions though, as your device may recognize that you
are to enter a different road section, as opposed to remaining on the
same (0x01) road.

It would be interesting to hear your results.

Hope this helps.