[GRASS5] detri license clarified (new hope for geom)

[David D Gray]

Markus Neteler wrote:
> 
> On Tue, Dec 05, 2000 at 04:39:31PM +0100, Andreas Lange wrote:
> > Hi,
> >
> > does this mean that the geom lib must be moved to src.nonGPL?
> > This would mean that s.geom and v.geom can no longer be used.
> >
> > I had a very superficial glance at geom and detri, but i can not say how
> > much work it will be to adapt s.geom and v.geom to this library.
> > And i am not able to do that.
> >
> > [...]
> 
> > The people working on the vector library should decide if we should
> > include the detri library. As far as i remember the detri library is 3D
> > and may be faster than gts (where the delaunay triangulation is only
> > 2D). But i am totally clueless, so that i can not recommend anything.
> David and Radim (and others), please advise us!
> 

For a later version of the vector library we want to have support for 3d
vector maps directly in the vector API itself. The idea is to use
triangulated surfaces as the geometric primitive. So a suitable library
would have to be able to do 3d triangulations, also would have to be
implemented as a well-exposed API - most of the triangulation hacks seem
to be end-use programs. I suspect that whatever is used will have to be
customised to some extent.

To create a suitable surface, triangulations should 

* be constrained so that triangles are moderately well-behaved, but this
should be flexible

* show some relationship between local cell size and relief, for example
larger triangles in regions of low curvature. But then - how is point
selection done?


There is another public domain (sensu stricto) implementation called
dewall, which does 3d  (http://vcg.iei.pi.cnr.it/DVRunstruct.html). The
documentation (dewall.pdf) gives some benchmarks for different
algorithms.

In sum, I don't have a clear idea yet how to get the details of the
vector library, but we need a triangulation API. If it's not Detri, it
would be something else, perhaps the precise method is not critical.

David

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