[mkgmap-dev] [PATCH] Access destination tag

Sun Mar 1 20:02:43 GMT 2009

Hi Johann,

> >> That's quite interesting! In my experiments, the access flags for  
> >> "delivery" and "emergency" didn't behave like the other six, so if  
> >> "delivery" is actually "destination", that'd be great.
> >>     
> I very well could imagine, this is the missing bit for 'destination'
> >
> > Yes, it would be great but do we actually know if the garmin is capable of
> > avoiding routing into an area if the destination is not within that area?
> >
> > At this time, I can't picture how the gps could work it out. It would have
> > to make nets of connected ways that all have that attribute to be able to
> > route into that area - it seems to be (potentially) very complicated.
> >
> >   
> I think the bit could mean 'dont use this street unless you must'. As 
> the routing algortihm works from both sides, the following would be 
> possible: If search is starting at such a road, it could take such roads 
> as long it finds the first road without this flag. From there on it is 
> not allowed to enter a road with delivery only. So there is no complex 
> routing network.
> 
> The only case which must be excluded in this scenario would be an 'isle' 
> of free roads inside other roads only usable for delivery.

I find it hard to believe the gps does all that.

> >> For the record, calling these fields DELIVERY and EMERGENCY has to do  
> >> with the cGPSmapper documentation: The RouteParams field ends in 8 bit  
> >> flags which are named according to the vehicle types. We're assuming  
> >> these 8 fields actually correspond to one byte in the IMG. This may be  
> >> off, or the cGPSmapper may be inaccurate.
> >>
> >> But having flags "no delivery" or "no emergency vehicles" on a road  
> >> doesn't make too much sense.
> >>     
> >
> > No, but having a flag "delivery allowed" or "emergency allowed" does -
> > imagine a pedestrian area that doesn't allow normal traffic but does
> > allow delivery vehicles and could be used by emergency vehicles. Such
> > areas exist, I have seen them.
> >
> >   
> Would in this case 'delivery allowed' not mean the same as 
> 'destination'?

No - if I live inside an area that is only reachable by ways marked by
"destination" then I want to be able to route in/out of the area
whether I am driving a delivery van or riding my bicycle!

Surely the problem here is that the OSM data can specify an attribute
of a way ("destination") that is, perhaps, not supported by the gps
units. It may be supported, but we don't know at this time for sure.

It certainly would be useful to understand how the delivery and
emergency bits function.

Cheers,

Mark