CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 08/26/2016 05:32 AM, zys wrote:
> <http://cgal-discuss.949826.n4.nabble.com/file/n4662163/snapshot_of_CGAL.jpg>
>
> The 3-D alpha shape demo shows alpha as percentage. What is the exact value
> of alpha?

The code used in the demo (demo/Alpha_shape_3/MainWindow.cpp) is the
following:


void
MainWindow::alphaChanged(int i)
{
  if (scene.alpha_shape.number_of_alphas() > 0){
    if(i < 100){
      int n = static_cast<int>((i * 
scene.alpha_shape.number_of_alphas())/ 100);
      if(n == 0) n++;
      scene.alpha_shape.set_alpha(scene.alpha_shape.get_nth_alpha(n));
    } else {
      Alpha_iterator alpha_end_it = scene.alpha_shape.alpha_end();
      scene.alpha_shape.set_alpha((*(--alpha_end_it))+1);
    }
  } else {
    scene.alpha_shape.set_alpha(0);
  }
  viewer->alphaChanged();
  Q_EMIT(alphaChanged());
}

It is based on the nth-alpha's.
If you want to see the current alpha, you can for example put a cout
near the calls to set_alpha()


Sebastien.

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