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add a geometric test to prevent folding and self-intersections

This commit is contained in:
Sébastien Loriot 2019-09-11 14:44:27 +02:00
parent 5e736889d2
commit 7cf0c7daad
1 changed files with 68 additions and 1 deletions
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69
Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/remove_degeneracies.h
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@ -119,6 +119,56 @@ void collect_badly_shaped_triangles(const typename boost::graph_traits<TriangleM
}
}
// Following Ronfard et al. 96 we look at variation of the normal after the collapse
// the collapse must be topologically valid
template <class TriangleMesh, class NamedParameters>
bool is_collapse_geometrically_valid(typename boost::graph_traits<TriangleMesh>::halfedge_descriptor h,
const TriangleMesh& tmesh,
const NamedParameters& np)
{
typedef typename boost::graph_traits<TriangleMesh>::halfedge_descriptor halfedge_descriptor;
typedef typename GetVertexPointMap<TriangleMesh, NamedParameters>::const_type VPM;
typedef typename boost::property_traits<VPM>::reference Point_ref;
typedef typename GetGeomTraits<TriangleMesh, NamedParameters>::type Traits;
VPM vpm = choose_param(get_param(np, internal_np::vertex_point),
get_const_property_map(vertex_point, tmesh));
/// @todo handle boundary edges
h = opposite(h, tmesh); // Euler::collapse edge keeps the target and removes the source
// source is kept, target is removed
CGAL_assertion( target(h, tmesh)==vertex_removed );
Point_ref kept = get(vpm, source(h, tmesh));
Point_ref removed= get(vpm, target(h, tmesh));
// consider triangles incident to the vertex removed
halfedge_descriptor stop = prev(opposite(h, tmesh), tmesh);
halfedge_descriptor hi = opposite(next(h, tmesh), tmesh);
std::vector<halfedge_descriptor> triangles;
while (hi!=stop)
{
if (!is_border(hi, tmesh))
{
Point_ref a = get(vpm, target(next(hi, tmesh), tmesh));
Point_ref b = get(vpm, source(hi, tmesh));
//ack a-b-point_remove and a-b-point_kept has a compatible orientation
/// @todo use a predicate
typename Traits::Vector_3 n1 = CGAL::cross_product(removed-a, b-a);
typename Traits::Vector_3 n2 = CGAL::cross_product(kept-a, b-a);
if ( n1*n2 <=0 )
return false;
}
hi = opposite(next(hi, tmesh), tmesh);
}
return true;
}
} // namespace internal
// @todo check what to use as priority queue with removable elements, set might not be optimal
@ -170,7 +220,6 @@ bool remove_almost_degenerate_faces(const FaceRange& face_range,
int kk=0;
std::ofstream(std::string("tmp/n-00000.off")) << tmesh;
#endif
while (!edges_to_collapse.empty())
{
edge_descriptor e = *edges_to_collapse.begin();
@ -211,6 +260,23 @@ bool remove_almost_degenerate_faces(const FaceRange& face_range,
}
h = opposite(h, tmesh);
}
if ( !internal::is_collapse_geometrically_valid(h, tmesh, np) )
{
h = opposite(h, tmesh);
if ( !internal::is_collapse_geometrically_valid(h, tmesh, np) )
{
#ifdef CGAL_PMP_DEBUG_REMOVE_DEGENERACIES
std::cerr << "Warning: geometrically invalid edge collapse! "
<< tmesh.point(source(e, tmesh)) << " "
<< tmesh.point(target(e, tmesh)) << std::endl;
#endif
next_edges_to_collapse.insert(e);
continue;
}
e = edge(h, tmesh); // update the edge
}
edges_to_flip.erase(e);
next_edges_to_collapse.erase(e); // for edges added in faces incident to a vertex kept after a collapse
#ifdef CGAL_PMP_DEBUG_REMOVE_DEGENERACIES_EXTRA
@ -332,6 +398,7 @@ bool remove_almost_degenerate_faces(const FaceRange& face_range,
if (undo)
{
/// @todo we could decide on a metric and allow the filp only if it is improving the mesh
Euler::flip_edge(h, tmesh); // avoid infinite loop: flip only if a cap is removed
// even if we inserted some edges above these will be tested before flipping (not optimal but it does not harm)
next_edges_to_flip.insert(e); // we add it for the next round in case some other flip fix the loop