[GRASS-user] gradient (slope) of a road

[Markus Neteler]

On Tue, May 31, 2011 at 9:22 AM, Francisco Calzada
<paco.calzada2000 at gmail.com> wrote:
> Dear list,
> I'm new to this list and I wonder if you could help me.

Welcome!

> I need to calculate the gradient (slope) of a road. I have a fine DEM to do
> it. The problem is when I run r.slope.aspect the resulting slope map have
> extremelly and odd high values. I don't know why. Do you? Anyway, could you
> tell me how do you calculate the slope of a road?

First use v.drape to drape the 2D road map over the DEM:
http://grass.osgeo.org/grass64/manuals/html64_user/v.drape.html

Then use the resulting 3D vector map to calculate the slope for
the vector segments using the "slope" method, results go into
the attribute table:
http://grass.osgeo.org/grass64/manuals/html64_user/v.to.db.html

Hope this helps
Markus