How does ros determine orientation?
I've got odometry data and it contains x,y,z odometry and orientation quarternions. But I dont know how does ros determine the x,y,z. I mounted lidar on top of my robot. So is x the same direction as the front of my lidar?
Usually, yes. See http://www.ros.org/reps/rep-0103.html and http://www.ros.org/reps/rep-0105.html