Improved handling of bounding polytope

include/osg/Plane

@@ -123,6 +123,14 @@ class OSG_EXPORT Plane
                    _fv[3];
         }
 
+        /** calculate the dot product of the plane normal and a point.*/
+        inline float dotProductNormal(const osg::Vec3& v) const
+        {
+            return _fv[0]*v.x()+
+                   _fv[1]*v.y()+
+                   _fv[2]*v.z();
+        }
+
         /** intersection test between plane and vertex list
             return 1 if the bs is completely above plane,
             return 0 if the bs intersects the plane,