Pure Pursuit
Linear and angular velocity control commands
Libraries:
Robotics System Toolbox /
Mobile Robot Algorithms
Navigation Toolbox /
Control Algorithms
Description
The Pure Pursuit block computes linear and angular velocity commands for following a path using a set of waypoints and the current pose of a differential drive vehicle. The block takes updated poses to update velocity commands for the vehicle to follow a path along a desired set of waypoints. Use the Max angular velocity and Desired linear velocity parameters to update the velocities based on the performance of the vehicle.
The look-ahead distance port and parameter compute a look-ahead point on the path, which is an instantaneous local goal for the vehicle. The angular velocity command is computed based on this point. Changing the look-ahead distance has a significant impact on the performance of the algorithm. A higher look-ahead distance results in a smoother trajectory for the vehicle, but can cause the vehicle to cut corners along the path. Too low of a look-ahead distance can result in oscillations in tracking the path, causing unstable behavior. For more information on the pure pursuit algorithm, see Pure Pursuit Controller.
Examples
Path Following with Obstacle Avoidance in Simulink®
Use Simulink to avoid obstacles while following a path for a differential drive robot. This example uses ROS to send and receive information from a MATLAB®-based simulator. You can replace the simulator with other ROS-based simulators such as Gazebo®.
Ports
Input
Pose — Current vehicle pose
[x y theta]
vector
Current vehicle pose, specified as an [x y theta]
vector, which corresponds to the x-y position and
orientation angle, theta. Positive angles are
measured counterclockwise from the positive
x-axis.
Waypoints — Waypoints
[ ] (default) | n-by-2 array
Waypoints, specified as an n-by-2 array of
[x y]
pairs, where n is the
number of waypoints. You can generate the waypoints using path planners
like mobileRobotPRM
(Robotics System Toolbox) or specify
them as an array in Simulink®.
Desired Linear Velocity — Linear velocity
scalar in meters per second
Desired linear velocity, specified as a scalar in meters per second. The controller assumes that the vehicle drives at a constant linear velocity and that the computed angular velocity is independent of the linear velocity.
Dependencies
To enable this port, select the Specify desired linear velocity from input port parameter.
Lookahead Distance — Look-ahead distance
scalar in meters per second
Look-ahead distance, specified as a scalar in meters per second. The look-ahead distance changes the response of the controller. A vehicle with a higher look-ahead distance produces smooth paths but takes larger turns at corners. A vehicle with a smaller look-ahead distance follows the path closely and takes sharp turns, but oscillate along the path. For more information on the effects of look-ahead distance, see Pure Pursuit Controller.
Dependencies
To enable this port, select the Specify lookahead distance from input port parameter.
Output
Linear Velocity — Linear velocity
scalar in meters per second
Linear velocity, returned as a scalar in meters per second.
Data Types: double
Angular Velocity — Angular velocity
scalar in radians per second
Angular velocity, returned as a scalar in radians per second.
Data Types: double
Target Direction — Target direction for vehicle
scalar in radians
Target direction for the vehicle, returned as a scalar in radians. The forward direction of the vehicle is considered zero radians, with positive angles measured counterclockwise. This output can be used as the input to the TargetDir port for the Vector Field Histogram block.
Dependencies
To enable this port, select the Show Target Direction output port parameter.
Parameters
Specify desired linear velocity from input port — Enable input port for desired linear velocities
off
(default) | on
Select this parameter to enable input of desired linear velocities at the Desired Linear Velocity input port.
Clear this parameter to specify desired linear velocity using the Desired linear velocity (m/s) parameter
Desired linear velocity (m/s) — Linear velocity
0.1
(default) | scalar
Desired linear velocity, specified as a scalar in meters per second. The controller assumes that the vehicle drives at a constant linear velocity and that the computed angular velocity is independent of the linear velocity.
Dependencies
To enable this parameter, clear the Specify desired linear velocity from input port parameter.
Maximum angular velocity (rad/s) — Angular velocity
1.0
(default) | scalar
Maximum angular velocity, specified as a scalar in radians per second. The controller saturates the absolute angular velocity output at the given value.
Specify lookahead distance from input port — Enable input port for look-ahead distances
off
(default) | on
Select this parameter to enable input of look-ahead distances at the Lookahead Distance input port.
Clear this parameter to specify desired linear velocity using the Lookahead distance (m) parameter
Lookahead distance (m) — Look-ahead distance
1.0
(default) | scalar
Look-ahead distance, specified as a scalar in meters. The look-ahead distance changes the response of the controller. A vehicle with a higher look-ahead distance produces smooth paths but takes larger turns at corners. A vehicle with a smaller look-ahead distance follows the path closely and takes sharp turns, but oscillate along the path. For more information on the effects of look-ahead distance, see Pure Pursuit Controller.
Dependencies
To enable this parameter, clear the Specify lookahead distance from input port parameter.
Show Target Direction output port — Target direction indicator
off
(default) | on
Select this parameter to enable the Target Direction output port. This port gives the target direction as an angle in radians from the forward position, with positive angles measured counterclockwise.
Simulate using — Type of simulation to run
Code generation
(default) | Interpreted execution
Interpreted execution
— Simulate model using the MATLAB® interpreter. This option shortens startup time but has a slower simulation speed thanCode generation
. In this mode, you can debug the source code of the block.Code generation
— Simulate model using generated C code. The first time you run a simulation, Simulink generates C code for the block. The C code is reused for subsequent simulations, as long as the model does not change. This option requires additional startup time, but the speed of the subsequent simulations is comparable toInterpreted execution
.
Tunable: No
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
Version History
Introduced in R2019bR2024a: Specify linear velocity and look-ahead distance at input ports, and renamed output ports
The Pure Pursuit block has two sets of changes:
You can now specify the desired linear velocity at the Desired Linear Velocity input port by selecting the Specify desired linear velocity from input port parameter.
You can now specify the desired linear velocity at the Lookahead Distance input port by selecting the Specify lookahead distance from input port parameter.
The output ports and a parameter have new names. This table shows the names prior to R2024a, and the names for R2024a and after.
Name Prior to R2024a Name for R2024a and after LinVel output port Linear Velocity output port AngVel output port Angular Velocity output port TargetDir output port Target Direction output port Show TargetDir output port parameter Show Target Direction output port parameter
See Also
Blocks
Classes
Topics
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