Resolve "Work on const / non-const in wolf base classes"

Closes #184 (closed)

src/processor/processor_odom_3D.cpp

@@ -56,7 +56,7 @@ void ProcessorOdom3D::computeCurrentDelta(const Eigen::VectorXs& _data,
         // rotation in quaternion form
         _delta  = _data;
         disp    = _data.head<3>().norm();
-        rot     = 2.0 * acos(_data(3));
+        rot     = 2.0 * acos(_data(6)); // '6' is the real part of the quaternion
     }
     /* Jacobians of d = data2delta(data, dt)
      * with: d =    [Dp Dq]