in calc_normal for EdgeHandle average incident face normals instead of incident vertex normals

src/OpenMesh/Core/Mesh/PolyMeshT.hh

@@ -456,13 +456,7 @@ public:
   }
 
   /// calculated and returns the average of the two vertex normals
-  Normal calc_normal(EdgeHandle _eh) const
+  Normal calc_normal(EdgeHandle _eh) const;
-  {
-    HalfedgeHandle _heh = this->halfedge_handle(_eh, 0);
-    VertexHandle vh0 = this->from_vertex_handle(_heh);
-    VertexHandle vh1 = this->to_vertex_handle(_heh);
-    return 0.5 * (this->calc_normal(vh0) + this->calc_normal(vh1));
-  }
 
   /** defines a consistent representation of a sector geometry:
       the halfedge _in_heh defines the sector orientation

src/OpenMesh/Core/Mesh/PolyMeshT_impl.hh

@@ -424,6 +424,28 @@ calc_normal(HalfedgeHandle _heh, const double _feature_angle) const
 //-----------------------------------------------------------------------------
 
 
+template <class Kernel>
+typename PolyMeshT<Kernel>::Normal
+PolyMeshT<Kernel>::
+calc_normal(EdgeHandle _eh) const
+{
+  Normal n(0);
+  for (int i = 0; i < 2; ++i)
+  {
+    const auto heh = this->halfedge_handle(_eh, i);
+    const auto fh = this->face_handle(heh);
+    if (fh.is_valid())
+      n += calc_normal(fh);
+  }
+  const auto length = norm(n);
+  if (length != 0)
+    n /= length;
+  return n;
+}
+
+//-----------------------------------------------------------------------------
+
+
 template <class Kernel>
 bool
 PolyMeshT<Kernel>::