[GRASS-dev] Re: v.net.path

[Markus Neteler]

On Sat, May 05, 2007 at 03:24:40AM +1200, Hamish wrote:
> Markus wrote:
> > OK, my mistake - the column should contain *costs*. That might be
> > the inverse of the speed limit, not the speed limit itself:
> > e.g.
> > # define traveling costs as inverse of speed limit:
> > v.db.update myroads col=forward val=1/50
> 
> ahh. Is "backward" really needed? (is it optional in d.path) I'm not
> really sure what that means actually. Does it mean it costs more to
> drive the wrong direction on a one way street? Harder to canoe upsteam?

It's for the cases that you have a two lane road (see NC dataset).
You can simulate traffic jam: say, morning time one lane, in
the evening the other lane. Or connect to some traffic service
which updates your DB in real time.

> > I have update the example in CVS. Please suggest if you have better
> > ideas.
> 
> For completeness: re speed limits- Expect 30mph on residential streets,
> 55mph on minor highways and up to 75mph on the interstate. This varies
> state to state & I'm not sure what the rules are in the Dakotas, but I
> expect they let you go pretty damn fast. :)
> 
> but google knows all:
>  http://www.iihs.org/laws/state_laws/speed_limit_laws.html

Cool. So we can improve it again...

Markus