[mkgmap-dev] Using exit refs in routing directions

Thu Jul 14 16:49:19 BST 2011

On 14/07/2011 11:05, Charlie Ferrero wrote:
> Hello list,
>
> Is there any way to get mkgmap to embed exit refs (where they exist) in
> the routing directions, so that instead of getting:
> "Exit right onto ramp" you get
> "Take exit 32 right onto ramp" or something similar?
>
> Is this something that official Garmin maps can do?
I think mkgmap needs some additional magic to incorporate exits in 
exactly the same way as Garmin does in the commercial maps. I have been 
experimenting with ways of improving the routing directions without any 
major changes to mkgmap and have been making some progress.

Firstly I am using destination=* and dest_ref=* on the ramps. This 
allows tagging to reflect what is useful for routing without getting 
into any conflicts about what the exit is *really* called. Some people 
tag the exit road itself with the exit number, whereas others tag  it 
with the ref-value from the motorway itself or from the road it leads 
onto. Giving the direction information its own tags allows for clear 
semantics.

To get these tags into the map I have a customised mkgmap style which 
overrides ref and name with dest_ref and destination respectively. This 
is an excerpt from my "lines" file:

# Set highway names to include the reference if there is one
# note: display_name is what the gps will show in the route instructions
(highway ~ '.*_link') & exit:to=* {set name='${exit:to}'}
(highway = motorway) & destination=* {set name='${destination}'}
(highway ~ '.*_link') & destination=* {set name='${destination}'}
(highway ~ '.*_link') & destination_ref=* {set ref='${destination_ref}'}
(highway ~ '.*_link') & dest_ref=* {set ref='${dest_ref}'}

Thereafter the standard rules take over.

Net result is that I get "keep right on A123 Townsville" which 
corresponds to the big signs approaching the exit and above the lanes. 
This is not exactly the same as "Take exit 32, on right, towards 
Townsville" which is the sort of thing you can get out of the Garmin 
with the commercial maps, but it makes the instructions *much* easier to 
follow.

What I am looking for now is a magic incantation to influence mappers 
into tagging consistently without overloading the semantics of existing 
keys or unnecessarily creating new ones.

Colin