[GRASS-user] v.net.iso usage - including speed as factor

[Darren Cope]

Hi all,

I'm trying to calculate drive time 'zones' using v.net.iso.  I've
worked through the examples using spearfish data, and seem to get
suitable results using only the line 'distance' as the factor.
However, I'd like to include the speed limit as another factor in the
calculation, and can't seem to find any examples of how to do this.

I've looked through the examples here:
http://grass.itc.it/grass64/manuals/html64_user/v.net.iso.html
and here:
http://www.dinama.gub.uy/grass/grass57/tutorial/network.html (which
mentions "This calculates the reachability map based on the vector
length for 1km, 2.5km, 5km and 10km. Another option were to use vector
line attributes from a DBMS table which may contain velocity, street
types etc." - so it appears to be possible!

Can anyone point out what I'm missing, and/or the appropriate command or switch?

Cheers,

Darren Cope
http://dmcope.freeshell.org
http://bluesignweekly.blogspot.com/