CGAL users discussion list

> On 12/10/07, 
> 
>  
> <>
>  wrote:
> > If not, is there a code example that iterates over
> > all of the exterior facets and provide both the
> > exterior polygon boundary and the any internal
> > polygon hole boundaries?
> 
> Hi Wayne,
> 
> The K-3D method to convert the Nef3 polyhedra back to K3-D mesh format
> requires exactly this info. The source can be seen on
> http://k3d.svn.sourceforge.net/viewvc/k3d/trunk/modules/booleans/conversion.cpp?view=markup
> 
> The to_mesh function on line 128 puts the points and the indices for
> face and hole loops in the arrays that are declared at the start of
> the function. Note that I am quite new to CGAL, and this probably is
> not the best method to convert from Nef3.

Bart:

Thank you for the pointer into your code.  I never really
understood it because I wasn't too sure what the K-3D
data structures were.

The algorithm I use is thus:

  foreach facet in facets {
     if facet.volume.mark {
         # We have a facet to be displayed:
         shalfedges := facet.shalfedges
         # Extract normal:
         nx := -facet.a
         ny := -facet.b
         nz := -facet.c
         # Visit each boundary/hole:
         is_outer := true
         is_hole := false
         for shalfedge in shalfedges {
            # Iterate around the boundary/hole:
            stop := shalfedge
            do {
                vertex := shalfedge.source.vertex
                shalfedge := shalfedge.prev
            } until shalfedge == stop
            is_hole := true
            is_outer := false
         }
      }
   }

I think the mail list manager is going to squeeze out
my pretty indentation, so you might have to reindent it
using the braces as a cue.

Cheers,

-Wayne