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

[Dylan Beaudette]

On Tue, May 31, 2011 at 8:54 AM, Markus Neteler <neteler at osgeo.org> wrote:
> 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

Markus' suggestion is the simplest. If you need more than slope,
consider densifying your line segments and sampling the raster of
interest along the new, shorter, segments. Here is the outline:

http://casoilresource.lawr.ucdavis.edu/drupal/node/698

Cheers,
Dylan