[GRASS-user] Calculating line length over terrain

[Falk Grossmann]

Dear Grass users,

My objective is to calculate the length of a line (GPS tracklog) in a very
mountainous terrain. In this case I will need to take into account the 3D
aspect. I see two ways of working this:

1) Converting the points to line vector and than using a DEM to calculate
the length. In ESRI software I would convert the DEM rasta to a TIN and than
overlay the line vector to calculate length. However, as DEM's in Africa are
course (and in the process of weaning myself of ESRI) I would imagine I
would be better of using something along the lines described bellow in
GRASS:

2) Use of the converted point to line vector and than incorporate the point
vector (GPS tracklog) which contains x,y,z data points to calculate the "3D"
element which needs to be added to the length. Maybe I need to segment the
line, than "extract" the slope of the line segments (from on GPS point to
the next) and than use the map calculator to get the length of each segment?

I wondering if there are any tools in GRASS which deal with this in one go
(maybe in the hydro tools or terrain?) For method 2 I am wondering how can
calculate the slop of a line - since the attributes are attached the the
start and stop GPS points of that segment.

Any suggestions much appreciated,

Thanks

Falk
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