difference between the various navigation packages

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hello, could someone briefly describe the diferences between the various ROS navigation packages? There's at least http://wiki.ros.org/navigation , http://wiki.ros.org/3d_navigation , and http://wiki.ros.org/nav2d . The description of http://wiki.ros.org/navigation says its a A 2D navigation stack but the video (with the PR2) shows it avoiding a 3D obstacle (person holding a plank). If it is indeed a 2D navigation stack what is nav2d for? If it is indeed a 3D navigation stack then what is 3d_navigation for?

thanks!