[mkgmap-dev] headout and turn instructions

Tue Feb 24 19:56:44 GMT 2009

On Feb 24, 2009, at 11:01, Robert Vollmert wrote:
> On Feb 23, 2009, at 20:31, Mark Burton wrote:
>>> I wonder what would happen if instead of changing the geometry, we
>>> just lied about the angles in NOD.
>>
>> That's a really interesting idea, can you try doing that sometime?
>
> Attached is a patch (compiles but untested) that should nudge the  
> headout of motorway exit link roads to the left by 15 degrees. It's  
> obviously a horrible hack, but it'd be interesting to see to what  
> extent it has any effect, in particular on turn instructions.

Some small tests indicate that headout does indeed affect the turn  
instructions: For one motorway exit (very slightly to the right), the  
instruction to exit was "Keep left" -- I forgot to switch the sign of  
the nudging. For one cross-roads where the route said to go straight  
on, I also got a "Keep left".

I didn't notice any bad effects due to the manipulated headout data,  
though I haven't checked route display at low zoom levels.

One instruction that impressed me was "Turn left to Schwäbische  
Straße", instructing me to turn into an unnamed footway that lead to  
Schwäbische Straße. That appears to be the difference between "to" and  
"on". I wonder if this also works for multi-routenode unnamed ways, or  
if possibly this feature requires links? It would probably be good if  
link roads did not get a label, so at motorway junctions you get  
instructions like "Keep right to A4" instead of "Keep right on <name/ 
ref of link road".

Anyhow, routing worked nicely and pointed out plenty of errors in the  
data. The routes are unfortunately not terribly good for bicycles.

Cheers
Robert