Local Planner
The global path that is given to the path follower, is first processed by a local planner, before the robot controller is called to generate movement commands. This local planner can be used to generate admissible paths, even when the global planner does not respect the robots kinematic constraints.
Local planners are also used for obstacle avoidance. They plan short paths multiple times per second, thus avoiding moving obstacles. Local planners are based on constraints and scorers, such as distance to the global path, distance to the obstacles and more.
For high speed navigation, local planners are indispensable because they can compensate errors due to the dynamics of the robot. The global path is then only used to guide the local planner in the desired direction.
The following figure demonstrates the local planner approach:
The green line is the global path and currently seen obstacles are shown in gold. In this case, the path is statically defined. The blue line is the current local path, which is correctly computed for the robots kinematics and the current pose.