How does DWA works in relation to global planner?

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I am also trying to sort out how this is working because I am having issues with it. But to answer your questions specifically

Looking at the ROS implementation here is more info on the inputs

The question about knowing where the obstacles are. It uses a costmap. This is set it initialize in dwa_planner_ros and then is passed to dwa_planner in its constructor

The question about the trajectory is the global plan This is set it initialize in dwa_planner_ros and then is passed to dwa_planner in its constructor. as fergs said the global plan is just a set of pose

Other information velocity max and mins are sent in and they are split into linear x and theta z velocities from the min (which should be negative) to the max and put into 2 array of potential velocities to be used. this is done in planner_util I think. Also the robot's current velocity and position are passed in.

DWA is really more of a controller - not a planner. Given a trajectory (which in ROS is simply an array of geometry_msgs/Pose), and the current position of the robot (again, another Pose message), it will compute the best command to apply to the mobile base at that instant in time (in ROS, a geometry_msgs/Twist message). If you run the DWA algorithm at a high enough frequency (20-50hz), you can "follow" the plan pretty accurately.

In the ROS implementation, the "trajectory" is nothing but a series of poses - there is no time-parameterization, etc. This trajectory is created by a global planner (which, really, is the only real "planner" since DWA really is more of a "controller").

The ROS implementations are located here: https://github.com/ros-planning/navig...