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

[Benjamin Ducke]

Hamish wrote:
> 
> For a long time it has been unclear to me, do kernels live in the
> middle of each face like an area centroid with 3D coordinates, or is it
> for true 3D topology like a single point somewhere within a closed
> volume defined by many faces.
> 
> ie would a cube get a single kernel in the center of it* or six
> kernels, one on each face?

That's exactly what I'd like to know too! My recent updates to v.hull
for generating 3D hulls from 3D points threw this one up.
I have decided to put one single kernel into the center of gravity for
the hull, as it seemed to me that this is the 3D equivalent to a 2D
boundary with one centroid.

However, if anyone here sees a need for adding kernels to all faces,
that would be a trivial thing I could add to v.hull (perhaps with
a flag to turn them on?).

> 
> [*] if kernel-as-center-of-volume that could hold attribute info like
> building address or geological mineral type. For kernel-on-face I can't
> think of what kind of attribute you would want to attach to a wall
> besides something obvious like "north facing".
> 
> Thus I'm leaning to the kernel-as-center-of-volume meaning.
> 
> In that case a TIN describing a DEM might just get a single kernel, in
> the middle of XY space and placed below the surface to describe the
> interior side. (?)
> 
> But it would probably only be meaningful for a closed TIN "sphere" of
> the entire geoid surface.
> 
> 
> ??,

Yes, this question would definitely be interesting to discuss for the
v.delaunay 3D update, too.

Benjamin

-- 
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