Fix tiny bug that was inadverted for years!

src/processor/processor_odom_3D.cpp

@@ -56,9 +56,9 @@ void ProcessorOdom3D::computeCurrentDelta(const Eigen::VectorXs& _data,
     else
     {
         // rotation in quaternion form
-        _delta = _data;
-        disp = _data.head<3>().norm();
-        rot = 2 * acos(_data(3));
+        _delta  = _data;
+        disp    = _data.head<3>().norm();
+        rot     = 2.0 * acos(_data(6)); // '6' is the real part of the quaternion
     }
     /* Jacobians of d = data2delta(data, dt)
      * with: d =    [Dp Dq]