CGAL users discussion list

[Daniel Duque Campayo <>]

Hello again,

From the lack of answers to my question, I gather there is no function to 
tell 
if a point is inside a triangle. For the record, I enclose a function I have 
written which seems to do the trick. The method is based on projecting a 
vector onto two of the sides of the triangle.

Best,

Daniel


// Check whether a point P is inside the (P0,P1,P2) triangle
// P should be coplanar to the triangle
bool is_in_triangle(
                    const Point& P0, const Point& P1, const Point& P2,
                    const Point& P) {
  Vector v1(P1,P0);
  Vector v2(P2,P0);
  Vector v(P,P0);

  double v1v1=v1.squared_length();
  double v2v2=v2.squared_length();
  double v1v2=v1*v2;
  double vv1=v*v1;
  double vv2=v*v2;

  double det=v1v1*v2v2-v1v2*v1v2;
  if(det==0) return false; // degenerate triangle
  double a=vv1*v2v2-vv2*v1v2;
  double b=vv2*v1v1-vv1*v1v2;

  if ((a<0) || (b<0)) return false;

  a/=det;
  b/=det;

  return (a+b) <= 1;

}

-- 
Daniel Duque
http://rincon.uam.es/dir?cw=950067138671875