[mkgmap-dev] Turn restrictions with role=via ways

Sun Mar 23 15:23:41 GMT 2014

On Sun, Mar 23, 2014 at 11:16:51AM +0100, Gerd Petermann wrote:
>I don't care whether the restrictions could be changed in OSM. I just 
>want to make sure that I translate them correctly we writing the img 
>file.

IMO, this is on the border of "garbage in, garbage out". If there are 
clear semantics of the role=via ways in turn restrictions that can be 
easily explained to a human or a computer, sure, they can be supported.  
It is a matter of finding balance of effort: will the implementation 
effort be smaller than the effort to map it in a simpler way?

It also is a matter of risk: can the more complex translation rule fail 
the "do what I mean" semantics that the mapper might have had in mind.  
In the example of the only_right_turn restriction from the parking lot 
driveway, we could accidentally introduce an only_straight_on 
restriction to the main road (prohibiting any left turns). I think that 
we would need some kind of regression tests for turn restrictions, or 
routing in general.

These examples can be fixed in the map data, and I plan to do so in the 
next few days. What cannot be fixed in the map data are no_u_turn 
restrictions on dual-oneways that use role=via ways.

	Marko