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

[Helena Mitasova]

In relation to handling of large data sets - changing the algorithm
may not solve the issue. I haven't tried it with larger data set but
based on my previous experiences it may get stuck on topology building.
So that would need to be solved first (and you cannot skip topology
this time, as we did with points, because the result are areas and
nothing would work with the resulting map without topology).

As for 3D - Benjamin, if you could just add the original z value to the
output vertices (the value for centroid can be computed by calling the
tin.c ) that will be sufficient to get the basic functionality and  
display
the resulting TIN in 3D. For more sophisticated triangulations using
the existing libraries would be a more comprehensive solution,
as suggested by Markus (as long as we can make them part of GRASS
distribution)

Helena

On Jan 28, 2008, at 4:40 AM, Benjamin Ducke wrote:

> I noticed this one too a few days back when I was looking for a
> 3D hull algorithm. Looks like a promising collection of algorithm
> for GRASS.
>
> However, for a quick fix of v.delaunay, as suggested by Helena:
> Might it not be enough to replace the 2D distance measure in
> v.delaunay with a 3D distance, so it will do the tesselation in
> 3D space correctly?
> I could try and find some time to look into that if you think
> it feasible.
>
> Benjamin
>
>
>
> Markus Neteler wrote:
>> On Jan 28, 2008 9:29 AM, Maris Nartiss <maris.gis at gmail.com> wrote:
>>> Fixing large dataset and 3D support problems would be a nice
>>> improvement of GRASS vector support :)
>>
>> Possibly we need to substitute the algorithm? I found for example
>> http://www.qhull.org/
>> "Qhull computes the convex hull, Delaunay triangulation, Voronoi
>> diagram, halfspace intersection about a point, furthest-site Delaunay
>> triangulation, and furthest-site Voronoi diagram. The software  
>> runs in
>> 2-d, 3-d, 4-d, and higher dimensions. Qhull implements the Quickhull
>> algorithm for computing the convex hull. It handles roundoff errors
>> from floating point arithmetic. Qhull also computes volumes, surface
>> areas, and approximations to the convex hull."
>>
>> (seems to be GPL compliant)
>>
>> Markus
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>>
>
> -- 
> Benjamin Ducke, M.A.
> Archäoinformatik
> (Archaeoinformation Science)
> Institut für Ur- und Frühgeschichte
> (Inst. of Prehistoric and Historic Archaeology)
> Christian-Albrechts-Universität zu Kiel
> Johanna-Mestorf-Straße 2-6
> D 24098 Kiel
> Germany
>
> Tel.: ++49 (0)431 880-3378 / -3379
> Fax : ++49 (0)431 880-7300
> www.uni-kiel.de/ufg
>
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