Fix the ear clipping

Ear clipping method get sometimes wrong result on some concave polygon.
The original isEar() method only check whether there is any point in
the triangle. It will get wrong result if the triangle don't have
inside point but is a concave point of the polygon. Check the triangle
each time in isEar() will fix this bug.

surface/src/ear_clipping.cpp

@@ -66,7 +66,7 @@ pcl::EarClipping::performProcessing (PolygonMesh& output)
 void
 pcl::EarClipping::triangulate (const Vertices& vertices, PolygonMesh& output)
 {
-  const int n_vertices = static_cast<const int> (vertices.vertices.size ());
+  const size_t n_vertices = static_cast<size_t> (vertices.vertices.size ());
 
   if (n_vertices < 3)
     return;
@@ -77,11 +77,9 @@ pcl::EarClipping::triangulate (const Vertices& vertices, PolygonMesh& output)
   }
 
   std::vector<uint32_t> remaining_vertices (n_vertices);
-  if (area (vertices.vertices) > 0) // clockwise?
-    remaining_vertices = vertices.vertices;
-  else
-    for (int v = 0; v < n_vertices; v++)
-      remaining_vertices[v] = vertices.vertices[n_vertices - 1 - v];
+
+  // put the clockwise check in the isEar() to fix complex situation's decompose bug
+  remaining_vertices = _Vertices.vertices;
 
   // Avoid closed loops.
   if (remaining_vertices.front () == remaining_vertices.back ())
@@ -157,12 +155,12 @@ pcl::EarClipping::isEar (int u, int v, int w, const std::vector<uint32_t>& verti
   p_w = points_->points[vertices[w]].getVector3fMap();
 
   const float eps = 1e-15f;
-  Eigen::Vector3f p_uv, p_uw;
-  p_uv = p_v - p_u;
-  p_uw = p_w - p_u;
+  Eigen::Vector3f p_vu, p_vw;
+  p_vu = p_u - p_v;
+  p_vw = p_w - p_v;
 
   // Avoid flat triangles.
-  if ((p_uv.cross(p_uw)).norm() < eps)
+  if ((p_vu[0] * p_vw[1] - p_vu[1] * p_vw[0] > 0) != ((p_vu.cross(p_vw)).norm() < eps))
     return (false);
 
   Eigen::Vector3f p;