[GRASS-user] COGO along a slope

Hamish hamish_nospam at yahoo.com
Mon Feb 26 23:55:58 EST 2007

Manuel Gimond wrote:
> Is there a module (or an easy solution) that will generate line 
> features from along-terrain COGO data and a DEM?
> m.cogo will generate [X,Y] values from COGO data, but it assumes that 
> the COGO distance measurements have been projected onto a horizontal 
> surface. The only work around I can think of requires computing slope 
> data (from a DEM for instance) to get at an average cosine of the 
> slope underlying each COGO line segment, then correct the COGO 
> distance to get its projected counterpart. For instance, an 
> along-terrain distance on a 45 degree slope of 100.0 meters should 
> translate to a distance of 70.7 meters on a projected plane. This 
> correction can be tedious if manually computed by hand (especially 
> since multiple iterations may be needed to compute the average slope 
> along a line segment). Any ideas?

r.profile, r.transect might help

r.los output map contains vertical angle to target


Maybe v.distance is 3D aware? (I'm not sure). r.distance? (long shot)


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