[GRASS-user] surface interpolation with breaklines

Vincent Bain bain at toraval.fr
Sun Feb 9 07:24:04 PST 2014

Le dimanche 09 février 2014 à 15:55 +0100, Maciej Sieczka a écrit :
> W dniu 09.02.2014 13:17, Vincent Bain pisze:
> > Perhaps a wiser solution would be to v.to.point (i) contour lines,
> > (ii) breaklines, then merge them in a single raster an run
> > r.surf.nnbathy.
> There is no need to v.to.points isolines before rasterizing them for 
> nnbathy. Unless you want to generalize the contour lines on purpose, 
> e.g. to minimize the staircase artifacts in the output raster map.

oops, sorry you are right : I forgot to say I first turn isolines to
points (v.to.points, with the vertices option).

> As to breaklines, if these are linear features that indicate
> surface discontinuity and have no elevation attribute, nnbathy has no
> use of them (which you know already). If they are vector isolines, just 
> rasterize them straight away. If these are vector 3d lines, you'd need 
> to rasterize them interpolating their elevation at each cell of the 
> output raster map, which v.to.rast can't do.

Here is my mistake. I have a 3d breaklines vector, and I expected
v.to.rast being able to (i) get vertices z values and (ii) interpolate z
between vertices...

>  At least it couldn't a few 
> years ago when I tried it. This could probably be approximated with 
> something like v.to.points -v -i dmax=<raster DEM resolution> + 
> v.to.rast, but that's suboptimal.
> > Finally I found on the web a custom solution based on a nice little
> > python script named tin2raster, you can find it at the address
> > bellow. I tried to contact Antonio, the guy who wrote it, but did not
> > get a reply :
> >
> > http://digilander.libero.it/antonioall/python_tin2raster.html
> That tool utilizes Vect_tin_get_z
> (http://grass.osgeo.org/programming6/tin_8c.html), which claims to be
> able to perform such interpolation, not only along a linear 3d feature, 
> but on faces as well. Nice.

> I don't know, but I'd like v.to.rast to provide such feature too.

understanding c libs content is definitely beyond my skills ! but in the
end, having a v.to.rast module able to handle 3d polylines and faces
would be really nice.


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