[GRASS-user] slope along defined section (e.g. road, stream,)

[Hamish]

Tim Michelsen wrote:
> I would like to get the slope of a defined section like a part of a
> river or a road.
> 
> The only post dealing with such a idea was left unanswered:
> [GRASSLIST:7280] Hazard Assessment
> -
> http://thread.gmane.org/gmane.comp.gis.grass.user/8702
> 
> My idea is the following:
> 1) define a starting vector point and a end vector point of a stream
> or road section. 
> 2) then run a module to calculate the slope along that section
> 3) add the slope to the attribute table of the stream/road vector
> 
> While point 1 and 2 are quite clear to me I would ask you for hints
> on how to calulate the slope as lined out in point 2.
> What I am looking into would be a slope version of d.measure...
> 
> To have an idea on what one could like to do with the results:
> * Get a first estimate (based on DEM resolution) on hydraulic
> gradients in rivers
> * assess the risk of certain roads in mountainious regions


A line can only hold a single attribute for its totality, if you want
variable attributes along the line you have to break it up into finite
segments.


ideas-
method 1:
- r.slope.aspect to create slope map
- v.to.rast the vector line
- use r.mapcalc to get the intersection of the slope values and line
- r.univar, etc.


method 2:
 break the line up into little segments and pull slope vales from a
raster map into those points.
- r.slope.aspect to create slope map
- v.to.points -i dmax=`g.region -g | grep res= ...`
   or v.lrs.segment
- v.db.addcol pointsmap column='DOUBLE slope'
- v.what.rast column=slope
- d.vect.thematic or 'd.vect.chart sizecol=slope' or 'd.vect wcolumn='

method 3:
 instead of slope at points along line split line into many small
segments and find the slope for each segment. Otherwise v.to.db slope
just acts between end nodes of line for overall line slope. I think you
need a 3D vector line for this to work? (v.extrude?)
- v.split
- v.to.db option=slope


Dave wrote: (2 years, 32 weeks, 4 days, 14 hours and 6 minutes ago)
> How can I extract the locations where the pipeline intersects the
> streams?

v.patch + 'v.clean tool=break error=cross_points' ?


Hamish






      ____________________________________________________________________________________
Never miss a thing.  Make Yahoo your home page. 
http://www.yahoo.com/r/hs