[GRASS-dev] convert 3D polygons or Tins to a DEM?

Martin Landa landa.martin at gmail.com
Sat Feb 2 08:59:12 EST 2008


Hi,

2008/1/30, Benjamin Ducke <benjamin.ducke at ufg.uni-kiel.de>:

> If we have 3D input points for the TIN construction, then
> the resulting triangles should be 3D face primitives not
> areas (of which I assumed they were 2D primitives in the
> GRASS vector model), shouldn't they?

AFAIU, face is 3D boundary, kernel is 3D centroid for volume (3D
corpus, the topological composition of faces and kernel). So resulting
triangles should be zero-height volumes (volumes constracted from one
face and kernel). ??

> We would then also be talking about kernels, not centroids,
> which should be placed in the 3D geometric center of each
> traingular face?

yes.

> Or am I getting this totally wrong?
>
> Also, it seems to me that for a 3D delaunay triangulation
> the algorithm has to search for the nearest point in 3D
> space, because if it uses a 2D search, than it will be fooled
> by undercutting points and triangulate the wrong
> point triplets (I admit that undercuts don't usually appear in terrain
> surface modelling, but I have some data where they do).
>
> I guess the problem of building topology for massive data sets should
> be solved in the GRASS vector libraries, not in individual modules?

Yes, it need to be solved on library level.

[snip]

Regards, Martin

-- 
Martin Landa <landa.martin at gmail.com> * http://gama.fsv.cvut.cz/~landa *


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