7.47 wavefront

Authors

Brian P. Gerkey gerkey(at)stanford.edu,Andrew Howard ahoward(at)usc.edu

Synopsis

The wavefront driver implements a simple path planner for a planar mobile robot. The underlying planner, which uses wavefront propagation, was written by Andrew Howard; the integration into Player was done by Brian Gerkey.

This driver works in the following way: upon receiving a new position target, a path is planned from the robot's current pose, as reported by the underlying localize device. The waypoints in this path are handed down, in sequence, to the underlying position device.

By tying everything together in this way, this driver offers the mythical ``global goto'' for your robot.

Interfaces

Supported interfaces:

• position

Required devices:

• position
• localize

Supported configuration requests:

• None.

Configuration file options

Name Type Default Meaning

position_index integer 0 Index of the underlying position device.

localize_index integer 0 Index of the underlying localize device.

map_filename string none Bitmap file containing map in which to plan.

map_scale float none Meters per pixels in map.

robot_radius length 0.15 Radius of robot.

safety_dist length robot_radius Distance to keep between robot and obstacles.

max_radius length 1.0 Distance beyond which is considered infinite for planning purposes (?)

dist_penalty float 1.0 Fudge factor to discourage cutting corners.

dist_epsilon length 3*robot_radius Distance from target position that will be considered acceptable.

angle_epsilon angle 10 degrees Angular difference from target angle that will be considered acceptable.

Notes

• This driver is new, not widely tested, and non-trivial to configure and use.
• There is currently no way to get feedback from the planner, such as: the current list of waypoints, the lack of a feasible path, or the achievement of the final goal.
• The underlying position device must be capable of doing position control (i.e., not velocity control), preferably with local obstacle avoidance (a very good candidate is the vfh driver).
• The underlying localize device must have already converged to a reasonable estimate of the robot's pose before targets are sent to this driver (otherwise results will be unpredictable at best).
• The target thresholds (dist_epsilon and angle_epsilon) should be greater than those thresholds in the underlying position device, assuming it's vfh. Otherwise, the underlying driver thinks the robot has reached a target, while the wavefront driver is still waiting.