CGAL users discussion list

[Sven Andres <>]

Ok, now I found a way to remove the facets that I didn't want - those 
facets closing the surrounded space.
I just inserted a call to "is_Gabriel" for selection.

I also found another way I could have tried if that would not have 
worked - 3D-Alpha-Shapes, but because it worked I didn't try...

Maybe when my collegue tried some other point-sets and has any problems 
with this current solution, or if I should ever have plenty of time and 
nothing to do with that...

With best regards,

Sven

Sven Andres schrieb:
> Hello everybody,
>
> since my first message ("[cgal-discuss] non-convex Objects from 
> Pointset") I did some more reading and trying and I found, that it 
> does not seem to change the shape of the resulting object if I just 
> change the triangulation-method. Maybe the created faces are slightly 
> different, but still the result is a closed model and not the surface 
> I'm looking for.
>
> For those who did not read my first request - I try to turn a set of 
> points (with free orientation in space) into a 3D-Model of the surface 
> described by the points - e.g. just a patch of a spheres outer hull, 
> not a closed object as though it was cut out of a massive sphere. I 
> got to a point where I can extract a set of faces describing the 
> closed object but that is not what I want... A possible way would be 
> to try to project the point-set onto a plane and do 2D-triangulation 
> but we did it like that in the past and we wanted to go away from 
> 2D-triangulation for we got errors on the boundaries with that approach.
>
> My collegue told me he knows about a program (geomagic) using CGAL 
> that offers an "open 3D triangulation" so that you can turn a set of 
> points describing a surface into a non-closed model of the described 
> surface. He suggested that this might work when using another 
> triangulation method or a different geometry-kernel, but I could not 
> find a way to do this yet...
>
> Since yesterday I went away from "triangulation" and read something 
> about ways to handle 3D-surfaces rather than bodies in CGAL.
>
> I read about "envelopes" and "surface_meshing". While surface-meshing 
> seemed like a step into the right direction it looks like it cannot be 
> used on a free set of points - without a complete description of the 
> surface, or at least one giving the possibility to interpolate between 
> given values.
>
> So here I go again. Can anybody give me a hint how to turn any set of 
> points measured from a surface into a set of faces describing the 
> surface?
> Is it possible with CGALs "surface-meshing" or do I need to go a 
> different way?
>
> Any help is absolutely appreciated.
>
> With best regards,
>
> Sven Andres
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