[GRASS-user] Re: How to extract one single contour.

[Marcello Gorini]

Also, even when I zoom in to extract only one contour, the exported points
are not always in order in the file, in a way that when I use it to plot in
another program as a line, it connects the points in a wrong way.

How can I export contours in an amenable way to use in other programs, such
as Matlab, for instance?

Thanks in advance.

Marcello.





Marcello Gorini wrote:
> 
> Dear all,
> 
> I am interested in extracting the longest -1,000 meter contour from a
> bathymetric DEM and to save it in a text file as points.
> 
> By doing:
> 
> r.contour in=my_dem out=contour levels=-1000
> v.to.points in=contour out=contour_points dmax=my_resolution
> v.out.ascii in=contour_points out=contour_points.txt fs=" " dp=4
> 
> ... I get a text file with the contour points, however, it includes many
> different isolated contours, all with the same category (1).
> 
> Since I need only the longest, I believe I need to separate the different
> contours, maybe assigning different categories somehow, then maybe
> updating the database with v.to.db using option=length and then
> v.db.select the longest contour.
> 
> But I am not very used to working with vectors, so I don't know if that's
> the correct approach (nor how to accomplish it), so I would appreciate
> very much any help.
> 
> Many thanks.
> 
> Marcello.
> 


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