[GRASS-user] Calculating line length over terrain

[Markus GRASS]

Falk Grossmann wrote:
> 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. 
Can't you import the tracklog as 3D line with v.in.ogr -z? The imported
vector may contain both points and lines. Then v.to.db option=length?

> 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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