Waypoint Follower

Follow waypoints for UAV

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Libraries:
UAV Toolbox / Algorithms

Description

The Waypoint Follower block follows a set of waypoints for an unmanned aerial vehicle (UAV) using a lookahead point. The block calculates the lookahead point, desired course, and desired yaw given a UAV position, a set of waypoints and a lookahead distance. Specify a set of waypoints and tune the lookahead distance and transition radius parameters for navigating the waypoints. The block supports both multirotor and fixed-wing UAV types.

Examples

Approximate High-Fidelity UAV Model with UAV Guidance Model Block

Prototype and tune a waypoint following navigation system by using a reduced-order model for UAV.

• Open Live Script

Tuning Waypoint Following Controller for Fixed-Wing UAV

Design and tune a waypoint following controller for a fixed-wing UAV by using the Guidance Model and Waypoint Follower blocks.

• Open Live Script

Ports

Input

Pose — Current UAV pose

[x y z chi] vector

Current UAV pose, specified as a [x y z chi] vector. This pose is used to calculate the lookahead point based on the input to the LookaheadDistance port. [x y z] is the current position in meters. chi is the current course in radians. The course input is used only when the waypoints are empty. The UAV course is the angle of direction of the velocity vector relative to north measured in radians.

Example: [0.5;1.75;-2.5;pi]

Data Types: single | double

Waypoints — Set of waypoints

n-by-3 matrix | n-by-4 matrix | n-by-5 matrix

Set of waypoints for the UAV to follow, specified as a matrix with number of rows, n, equal to the number of waypoints. The number of columns depend on the Show Yaw input variable and the Transition radius source parameter.

Each row in the matrix has the first three elements as an [x y z] position in the sequence of waypoints.

If Show Yaw input variable is checked, specify the desired yaw angle, yaw, as the fourth element in radians.

If Show Yaw input variable is unchecked, and Transition radius source is external, the transition radius is the fourth element of the vector in meters.

If Show Yaw input variable is checked, and Transition radius source is external, the transition radius is the fifth element of the vector in meters.

The block display updates as the size of the waypoint matrix changes.

Data Types: single | double

LookaheadDistance — Lookahead distance

positive numeric scalar

Lookahead distance along the path, specified as a positive numeric scalar in meters.

Data Types: single | double

Output

LookaheadPoint — Lookahead point on path

[x y z] position vector

Lookahead point on path, returned as an [x y z] position vector in meters.

Data Types: single | double

DesiredCourse — Desired course

numeric scalar

Desired course, returned as numeric scalar in radians in the range of [-pi, pi]. The UAV course is the angle of direction of the velocity vector relative to north measured in radians. For fixed-wing type UAV, the values of desired course and desired yaw are equal.

Data Types: single | double

DesiredYaw — Desired yaw

numeric scalar

Desired yaw, returned as numeric scalar in radians in the range of [-pi, pi]. The UAV yaw is the forward direction of the UAV regardless of the velocity vector relative to north measured in radians. The desired yaw is computed using linear interpolation between the yaw angle for each waypoint. For fixed-wing type UAV, the values of desired course and desired yaw are equal.

Data Types: single | double

LookaheadDistFlag — Lookahead distance flag

0 (default) | 1

Lookahead distance flag, returned as 0 or 1. 0 indicates lookahead distance is not saturated, 1 indicates lookahead distance is saturated to minimum lookahead distance value specified.

Data Types: uint8

CrossTrackError — Cross track error from UAV position to path

positive numeric scalar

Cross track error from UAV position to path, returned as a positive numeric scalar in meters. The error measures the perpendicular distance from the UAV position to the closest point on the path.

Dependencies

This port is only visible if Show CrossTrackError output port is checked.

Data Types: single | double

Status — Status of waypoint navigation

0 | 1

Status of waypoint navigation, returned as 0 or 1. When the follower has navigated all waypoints, the block outputs 1. Otherwise, the block outputs 0.

Dependencies

This port is only visible if Show UAV Status output port is checked.

Data Types: uint8

Parameters

UAV type — Type of UAV

fixed-wing (default) | multirotor

Type of UAV, specified as either fixed-wing or multirotor.

This parameter is non-tunable.

StartFrom — Waypoint start behavior

first (default) | closest

Waypoint start behavior, specified as either first or closest.

When set to first, the UAV flies to the first path segment between waypoints. If the set of waypoints input in Waypoints changes, the UAV restarts at the first path segment.

When set to closest, the UAV flies to the closest path segment between waypoints. When the waypoints input changes, the UAV recalculates the closest path segment.

This parameter is non-tunable.

Transition radius source — Source of transition radius

internal (default) | external

Source of transition radius, specified as either internal or external. If specified as internal, the transition radius for each waypoint is set using the Transition radius (r) parameter in the block mask. If specified as external, specify each waypoints transition radius independently using the input from the Waypoints port.

When the UAV is within the transition radius, the block transitions to following the next path segment between waypoints.

This parameter is non-tunable.

Transition radius (r) — Transition radius for waypoints

10 (default) | positive numeric scalar

Transition radius for waypoints, specified as a positive numeric scalar in meters.

When the UAV is within the transition radius, the block transitions to following the next path segment between waypoints.

This parameter is non-tunable.

Minimum lookahead distance (m) — Minimum lookahead distance

0.1 (default) | positive numeric scalar

Minimum lookahead distance, specified as a positive numeric scalar in meters.

When input to the LookaheadDistance port is less than the minimum lookahead distance, the LookaheadDistFlag is returned as 1 and the lookahead distance value is specified as the value of minimum lookahead distance.

This parameter is non-tunable.

Hover at last waypoint — Lookahead point location at last waypoint

off (default) | on

The location of Lookahead point at the end of waypoint navigation. If enabled, the lookahead point remains stationary at the last waypoint. If disabled, the lookahead point continues to traverse the straight-line path connecting the last two waypoints.

This parameter is non-tunable.

Dependencies

To enable this parameter, set UAV type to multirotor

Show Yaw input variable — Accept yaw input for waypoints

off (default) | on

Accept yaw inputs for waypoints when selected. If selected, the Waypoints input accepts yaw inputs for each waypoint.

Show CrossTrackError output port — Output cross track error

off (default) | on

Output cross track error from the CrossTrackError port.

This parameter is non-tunable.

Show UAV Status output port — Output UAV waypoint status

off (default) | on

Output UAV waypoint status from the Status port.

This parameter is non-tunable.

Simulate using — Type of simulation to run

Interpreted execution (default) | Code generation

• Interpreted execution — Simulate model using the MATLAB^® interpreter. This option shortens startup time but has a slower simulation speed than Code 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 to Interpreted execution.

This parameter is non-tunable.

Tunable: No

More About

Waypoint Hyperplane Condition

When following a set of waypoints, the first waypoint may be ignored based on the pose of the UAV. Due to the nature of the lookahead distance used to track the path, the waypoint follower checks if the UAV is near the next waypoint to transition to the next path segment using a transition region. However, there is also a condition where the UAV transitions when outside of this region. A 3-D hyperplane is drawn at the next waypoint. If the UAV pose is inside this hyperplane, the waypoint follower transitions to the next waypoint. This behavior helps to ensure the UAV follows an achievable path.

The hyperplane condition is satisfied if:

(p-w1)^T (w2-w1) ≥ 0

p is the UAV position, and w1 and w2 are sequential waypoint positions.

If you find this behavior limiting, consider adding more waypoints based on your initial pose to force the follower to navigate towards your initial waypoint.

References

[1] Park, Sanghyuk, John Deyst, and Jonathan How. "A New Nonlinear Guidance Logic for Trajectory Tracking." AIAA Guidance, Navigation, and Control Conference and Exhibit, 2004.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2018b

R2024b: Hover at last waypoint

You can now configure the lookahead point to remain stationary at the final waypoint by enabling the Hover at last waypoint parameter. This parameter is only available when you set UAV Type as multirotor.