[mkgmap-dev] Access handling trunk <=> mergeroads branch

Sat Nov 30 01:14:38 GMT 2013

WanMil <wmgcnfg at web.de> writes:

> I am comparing differences between the mergeroads branch running the
> compatibility mode and the trunk.
>
> Having the following way:
>  access = destination
>  highway = path
>
> The access bits are set as:
>                trunk | branch
> no_car       |   0   |    1
> no_bus       |   0   |    1
> no_taxi      |   0   |    1
> no_foot      |   0   |    0
> no_bike      |   0   |    1
> no_truck     |   0   |    1
> no_throughrt |   1   |    1
> delivery     |   0   |    1
> emergency    |   0   |    1
>
> 0 = bit is not set
> 1 = bit is set
>
> For delivery and emergency I am not sure if delivery/emergency is
> allowed if the bit is set or unset.
>
> At the moment the trunk allows all type of vehicles to use the given
> way. I think that's not good. The branch allows only foot to use the
> way.  What do you think should be the correct access bit mask for the
> given way?

I see multiple interlinked questions here.

One is if a given vehicle can physically use the way.  For highway=path,
I would say that car, bus, taxi, truck, delivery, emergency cannot.  If
they could, it would be highway=track instead.  So some of these bits
should not be set even for highway=path with access=yes (default case).
Or perhaps I'm confused and there is some other mechanism for this.

The other question is access=destination.  That's supposed to encode a
legal notion that one may traverse the way only if it's necessary to get
someplace that you can legally go.   My understanding of the Garmin
routing behavior is that it will not use disallowed ways in a route,
except at the ends.

So what this leaves me failing to grasp (and which I think is at the
heart of deciding the right answer to your query) is how these no_* bits
relate to a) physical feasibility, which can not be overridden by
'necessary to get to destination'  and b) permission, which seems to be
overriden.
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