CODEWITHSUNDEEP
c++geometrycgaltriangulation
quaternionboy
quaternionboy

Reputation: 361

Extracting normals of a CGALTriangulation

In a 3D CGALTriangulation I'm trying to get the normals by this way

    Vector n = CGAL::normal(p1, p2, p3);

Code in context:

for (CGALTriangulation::Finite_facets_iterator it = T.finite_facets_begin();
             it != T.finite_facets_end();
             it++)
        {
            std::pair<CGALTriangulation::Cell_handle, int> f = *it;
            
            const Pointt& p0 = f.first->vertex((f.second))->point();
            
            const Pointt& p1 = f.first->vertex((f.second+1)&3)->point();
            const Pointt& p2 = f.first->vertex((f.second+2)&3)->point();
            const Pointt& p3 = f.first->vertex((f.second+3)&3)->point();

EDIT

for (auto f : T.finite_facets())
{

    //all convex hull facets pointing outside
    if (T.is_infinite(T.mirror_facet(f).first)){
        f = T.mirror_facet(f);
    }

    const auto cell = f.first;
    const int i = f.second;
        
    const Point& p1 = cell->vertex( T.vertex_triple_index(i, 0) )->point();
    const Point& p2 = cell->vertex( T.vertex_triple_index(i, 1) )->point();
    const Point& p3 = cell->vertex( T.vertex_triple_index(i, 2) )->point();

    Vector n = CGAL::normal(p1, p2, p3);
}

Upvotes: 0

Views: 117

Answers (1)

lrineau
lrineau

Reputation: 6274

The orientation of a facet cannot be found that way. To set p1, p2, and p3, use that piece of code:

const auto cell = f.first;
const int i = f.second;

const Pointt& p1 = cell->vertex(T.vertex_triple_index(i, 0)->point();
const Pointt& p2 = cell->vertex(T.vertex_triple_index(i, 1)->point();
const Pointt& p3 = cell->vertex(T.vertex_triple_index(i, 2)->point();

See the documentation of vertex_triple_index.

Upvotes: 3

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