can't call member without object?

edit

i'm using ros kinetic.

In file included from /home/robot/youbot_catkin_ws/src/youbot-controller/src/localisation-component.cpp:1:0:
/home/robot/youbot_catkin_ws/src/youbot-controller/src/localisation-component.hpp: In member function ‘virtual void Localisation::updateHook()’:
/home/robot/youbot_catkin_ws/src/youbot-controller/src/localisation-component.hpp:37:80: error: cannot call member function ‘void KDL::Rotation::GetQuaternion(double&, double&, double&, double&) const’ without object
             KDL::Rotation rot = KDL::Rotation::GetQuaternion(qu.x, qu.y, qu.z, qu.w);
                                                                                    ^
    youbot-controller/CMakeFiles/localisation-component.dir/build.make:62: recipe for target 'youbot-controller/CMakeFiles

/localisation-component.dir/src/localisation-component.cpp.o' failed
    make[2]: *** [youbot-controller/CMakeFiles/localisation-component.dir/src/localisation-component.cpp.o] Error 1
    CMakeFiles/Makefile2:407: recipe for target 'youbot-controller/CMakeFiles/localisation-component.dir/all' failed
    make[1]: *** [youbot-controller/CMakeFiles/localisation-component.dir/all] Error 2
    Makefile:138: recipe for target 'all' failed
    make: *** [all] Error 2
    Invoking "make -j4 -l4" failed

here is d source file:

#ifndef OROCOS_LOCALISATION_COMPONENT_HPP
#define OROCOS_LOCALISATION_COMPONENT_HPP

    #include <rtt/RTT.hpp>
    #include <iostream>
    #include <geometry_msgs/Pose2D.h>
    #include <geometry_msgs/TransformStamped.h>
    #include <kdl/frames.hpp>

    class Localisation
        : public RTT::TaskContext
    {
        geometry_msgs::TransformStamped tfs;
        RTT::OutputPort<geometry_msgs::Pose2D> outpose;
     public:
        Localisation(std::string const& name)
            : TaskContext(name, PreOperational)
        {
        addPort("pose", outpose).doc("Contains latest Youbot Pose.");
    }

    bool configureHook() {
        /** Check in here that we can call rtt_tf */
        return false;
    }

    void updateHook() {
        try {
            /* tfs = ...call rtt_tf and query the transform /odom to /base_footprint ... ; */
        } catch (...) {
            return;
        }
        geometry_msgs::Pose2D pose;
        pose.x = tfs.transform.translation.x;
        pose.y = tfs.transform.translation.y;
        geometry_msgs::Quaternion qu = tfs.transform.rotation;
        KDL::Rotation rot = KDL::Rotation::GetQuaternion(qu.x, qu.y, qu.z, qu.w);
        //KDL::Vector v;
        //pose.theta = rot.GetRotAngle(v);
        //outpose.write(pose); 
    }
};

#endif