Thanks for your reply, I want to know how to access the sensors data (sonar,laser,odometry) and how to send velocity commands using p2os in ROS. Its ok that it can be controlled by keyboard (there is one node that I 'll test it tomorrow), but I want to write separate x.cpp file, there I want to access sensors data and then I can move ahead like obstacle avoidance [for the time being] and more. There after I 'll go to navigation stack. Is it possible for you to send a test program, say for sonar obstacle avoidance [like we have in Player]?