[mkgmap-dev] Possible maxspeed patch

Sun Aug 30 23:20:46 BST 2009

MarkS wrote:
> Greg Troxel wrote:
>
>   
>> This all makes sense, but it seems that the real problem needs to be
>> solved at the database semantics level.
>>     
>
> I agree with the principle. However, I guess a limitation on mkgmap 
> routing is that mkgmap doesn't do the routing it supplies that data to 
> garmin who do the routing. We can affect the data going in but not the 
> routing algorithms. I was testing yesterday and road speed doesn't seem 
> to make much difference to mapsource routes. Mapsource seems to follow 
> the road class (set in preferences) and only allows speed to affect the 
> route if it makes a major difference.
>   

I see two separate problems here:
One is how to indicate to a routing engine what the likely speed for a 
way is.
The second is, for a given routing engine, how to actually achieve 
passing that data.

I'm with Grex Troxel and the others in thinking that "maxspeed=" should 
reflect the legal limit.
I can see numerous cases in my area however where the likely speed of a 
route is *way* lower than that, and we need a way to flag it. Someone 
suggested "routingspeed=" which sounds fine to me.

Let's try and remember that we shouldn't try to munge OSM's data to suit 
the Garmin routing engines. There are other routers with OSM support 
(Android GSM-equipped phones for instance). I got caught in the trap of 
"adapting" OSM to suit my Streetpilot before a friend with an Android 
pointed out that it was causing his unit to issue silly driving 
instructions.

We certainly shouldn't muck about with "maxspeed=".
How do we go about getting "routingspeed=" adoped?

We presumably also adopt a standing rule along the lines of "default 
routingspeed is 80% of maxspeed if 'routingspeed=' isn't stated" or 
something like that. Anyone got a better default rule?

Steve
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