Using PCL with ROS

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Hi!

I am new to ros. I have just recorded a ros bag file using stereo camera. Now I want to perform point cloud registration. I got to know that pcl would suffice for that but I don't know how to use it. Do I need to git clone the library from https://github.com/PointCloudLibrary/... ?? Also I observed that there in a package named pcl_ros in my /opt/ros folder but it does not contain any file for registration. What is its use then??

Thanks in advance