My advisor gave me a bag file for a pr2 robot, which includes three kinds of
topic, namely sensor_msgs/pointcloud, sensor_msgs/pointcloud2 and
tf/tfmessage. 
I want to get the robot motion information and the obstacle position
information. From the tf document I can get two kinds of information. One
kind is of a tree  to introduce the relationship of different links. But the
other kind like this:
transforms
	[0]
		header
			seq: 0
			stamp: 1274768649205000409
				secs: 1274768649
				nsecs: 205000409
			frame_id: /odom_combined
		child_frame_id: /base_footprint
		transform
			translation
				x: 2.12986805655
				y: -0.140524320055
				z: 0.0
			rotation
				x: 0.00490979815527
				y: 0.00847065476276
				z: 0.721995381834
				w: 0.691828599077
I want to know  how to use the translation and rotation operations.
Another question is about the sensor_msgs/pointcloud topic. In the
sensor_msgs/pointcloud document, I don't know how to use the index, distance
and timestamp channel. I want to know how to find the help document.
Thank you.
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