reading xyz form tf/tfMessage

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hello, I am trying to read xyz from tfMessage which publishes the kinect's translation from the pi_tracker or the openni_launch and i want it sent to tum_simulator..

where is the code

geometry_msgs::Twist command;
ros::Publisher pub_takeoff, pub_land, pub_toggle_state, pub_vel;
geometry_msgs::TransformStamped transforms;
geometry_msgs::Transform transform;
geometry_msgs::Vector3 translation;


using namespace ros;

void chatterCallback(const tf::tfMessage::ConstPtr& mes)

{

    //command.linear=mes;
    command.linear.x = mes->transforms.transform.translation.x;
    //command.linear.y = mes->y;
    //command.linear.z = mes->z;
    //command.angular.z= mes->z;
ROS_INFO("I received %f %f %f %f/n", command.linear.x, command.linear.y, command.linear.z, command.angular.z);
}


int main(int argc, char **argv) {

 //init subscr node
ros::init(argc, argv, "simkin");
// Create a node handle
ros::NodeHandle n;
// Initialize the node
ros::Subscriber sub = n.subscribe("/tf", 1000, chatterCallback);
//ros::spin();


 // A publisher for the movement data
 Publisher pub = n.advertise<geometry_msgs::Twist>("/cmd_vel", 10);

 // Drive forward at a given speed.  The robot points up the x-axis.
 //geometry_msgs::Twist command;


 Rate rate(10);
 while (ok()) {
   pub.publish(command);
   rate.sleep();
   ros::spinOnce();
 }

 return 0;
}