[GRASS-user] surface interpolation with breaklines

[Vincent Bain]

Thanks you Antonio,

in my present case, half a cell offset did not matter in any way, but I
notice your modification.
Your script might be well appreciated in the community....
My suggestion was to complete the v.to.rast module so it could handle 3d
geometries (3d polylines and faces), unfortunately I am only good at
scripting in bash (my knowledge of python and C are too poor to pretend
doing that). 

Bye,
Vincent.


Le mardi 11 février 2014 à 09:05 +0100, antonioall at libero.it a écrit :
Hello Vincent,
> Excuse me for my bad English.
> Certainly you can cite me and my job.
> Attention: the program considers as reference the angle in low at
left 
> of the cell and not the central point.
> Reading the documentation of Grass found in net, I don't understand
what 
> reference is used for the cells.
> If the reference of the cell is its central point, the lines 115 and
116 
> of the script become:
>              x = xref + j * xres + 0.5 * xres
>              y = yref + i * yres + 0.5 * yres
> If you find useful information on the matter, please update me.
> 
> Good job,
> Antonio Alliegro



Le dimanche 09 février 2014 à 16:24 +0100, Vincent Bain a écrit :
> 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.
> 
> 
> Best,
> Vincent.
> 
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