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Forum: Geometry
Re: Question Polyhedron::SetReferences: List N is not empty (Nicola Mori)
Re: None Re: Polyhedron::SetReferences: List N is not empty (John Allison)
Re: More Re: Polyhedron::SetReferences: List N is not empty (Nicola Mori)
Re: None Re: Polyhedron::SetReferences: List N is not empty (John Allison)
Date: 09 Apr, 2015
From: Nicola Mori <Nicola Mori>

With a better understanding of the polyhedron dump (thanks John) I have been able to find the reason of the messages. It is because my facets, in more complex settings, can have more than one neighbouring facet per side. For example, it might happen this:

  *----*----*
  |    |    |
  | 1  |    |
  |    |    |
  *----* 3  |
  |    |    |
  | 2  |    |
  |    |    |
  *----*----*

i.e. the left side of the quadrangular facet 3 is the neighbour of both facet 1 and 2. But the neighbourhood is obviously not recognized, since in general the three facets can lie in different planes (while for my case they are indeed in the same plane).

In my geometry this happens because what I'm trying to do is to implement is a terrain starting from terrain height measurements on a (x,y) grid, I interpolate between the heights using triangular facets, but to close the solid I have to create side faces and a bottom face. The side faces requires to reproduce the height profile at the border of the map, e.g.:

  z ^    *            
    |    |\       *   
    |    | \     /|\
    |    |  \   / | \
    |    |   \ /  *--*
    |    *----*---*  |\
    |    |    |   |  | \ /
    |    |    |   |  *--*
    |    |    |   |  |  |
    |    *----*---*--*--*-
    |   
    -----------------------> x

In the above tessellation there is no perfect match between the sides of adjacent facets, but I cannot refine the tessellation since each point can have a different z so too many facets will be produced.

In the end I solved the problem by expanding the grid with rows and columns at constant z, to flatten the profile of the border and avoid the need of a refined tessellation of the side faces to follow the profile of the border.

Thanks again for your precious help, John.

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