Reference Path Generator

Generate vehicle reference pose and path curvatures

Since R2026a

• 

Libraries:
Vehicle Dynamics Blockset / Vehicle Scenarios / Drive Cycle and Maneuvers

Description

The Reference Path Generator block fits a clothoid curve to user-defined waypoints to generate vehicle reference pose and path curvature. Clothoid curves have curvature that varies linearly with distance traveled, making them ideal for generating smooth, easily navigable trajectories. The block calculates the nearest path using instantaneous vehicle position and computes a reference horizon over a specified length and number of samples for use by a driver block. Select either closed or open-ended waypoints, and specify the distance to search ahead for the nearest waypoint to the vehicle to identify the starting reference point.

The figure shows how the Reference Path Generator block generates the reference horizon from the fitted path. Blue circles represent the specified waypoints, Reference path waypoints, refPathXY [m], connected by a smooth clothoid curve. From the vehicle's current position and orientation specified by the block inputs, X, Y, and psi, the block identifies the nearest point on the path and computes a specified number of evenly spaced points ahead, shown as red circles. These points form the output reference path, DrvRef, used for trajectory planning. The first point is the closest reference location, while the last point lies at a distance, Path search distance, wayptSrchDist [m], along the path from the vehicle position, ensuring a continuous horizon.

Examples

Generate Skidpad Test

Generate skidpad tests for student competitions. View simulation in 3D environment.

• Open Live Script

Follow Waypoints Around Oval Track

Simulate vehicle driving around oval track specified by waypoints. Model loads a minimum number of waypoints and uses a MATLAB^® function to determine the next heading waypoint.

• Open Model

Ports

Input

X — Longitudinal position of vehicle center of mass

scalar

Longitudinal position of the vehicle center of mass in the global coordinate system. This input is required to verify that the vehicle has reached the XGate location to initiate the test procedure.

Data Types: single | double

Y — Lateral position of the vehicle center of mass

scalar

Lateral position of the vehicle center of mass in the global coordinate system. This input is required to generate an appropriate reference pose.

Data Types: single | double

psi — Vehicle yaw angle

scalar in the range [-pi, pi]

Vehicle yaw angle with respect to the global coordinate system. This input is required to generate an appropriate reference pose.

Data Types: single | double

Output

DrvRef — Driver reference data

bus

Driver reference data, returned as a bus containing these block values.

Signal	Description	Units
LngRef	Longitudinal reference velocity	m/s
LtrRef	Lateral reference displacement	m
XRef	Vehicle global longitudinal reference position	m
YRef	Vehicle global lateral reference position	m
PsiRef	Vehicle global yaw reference position	rad
CurvRef	Reference path curvature	1/m
CurvGradRef	Reference path curvature gradient	1/m^2

Data Types: bus

DrvCmd — Driver command data

bus

Driver command data, returned as a bus containing these block values.

Signal		Description
SteerCmd	EnblSteerCmd	Boolean signal used to override driver model steering commands
	SteerCmd	Handwheel angle, in radians
	SteerZero	Boolean signal used to override driver model steering commands with zero when value is true
	SteerHld	Boolean signal used to hold the current driver model steering output when true
AccelCmd	EnblAccelCmd	Boolean signal used to override driver model acceleration commands
	AccelCmd	Normalized accelerator input
	AccelHld	Boolean signal used to hold the current driver model acceleration output when true
	AccelZero	Boolean signal used to override driver model acceleration commands with zero when value is true
DecelCmd	EnblDecelCmd	Boolean signal used to override driver model deceleration commands
	DecelCmd	Normalized decelerator or brake input
	DecelHld	Boolean signal used to hold the current driver model deceleration output when true
	DecelZero	Boolean signal used to override driver model deceleration commands with zero when value is true
	HndBrkCmd	Normalized handbrake or park brake input
TransCmd	TransModeCmd	Command to specify the transmission mode
	GearCmd	Command to specify manual gear number or automatic transmission shifter position
	UpShiftCmd	Command to upshift
	DwnShiftCmd	Command to downshift
	ClutchCmd	Normalized clutch open command for manual transmissions

Data Types: bus

Parameters

To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Reference path waypoints, refPathXY [m] — Reference path waypoints

n-by-3 array

Reference path waypoints specified as an n-by-3 array where n is the number of waypoints, in m. Optionally, you can specify a third column in the array of path tangent angles which will be enforced during the fitting process. This can lead to more precise and consistent fitting.

Note

To get a good path fit, you may need to experiment with increasing or decreasing the number of points in areas of the path where greater precision is needed.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

To get the block parameter value programmatically, use the get_param function.

Parameter:	refPathXY
Values:	n-by-3 array
Data Types:	single | double

Path search distance, wayptSrchDist [m] — Path search distance

100 (default) | scalar in the range (0, inf)

Path search distance, in m.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

To get the block parameter value programmatically, use the get_param function.

Parameter:	wayptSrchDist
Values:	100 (default) | scalar in the range (0, inf)
Data Types:	single | double

Example: wayptSrchDist=80

Number of sample points to calculate the path horizon, numHrznPts [] — Number of sample points

20 (default) | scalar in the range [1,inf)

Number of sample points to calculate the path horizon.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

To get the block parameter value programmatically, use the get_param function.

Parameter:	numHrznPts
Values:	20 (default) | scalar in the range [1,inf)
Data Types:	single | double

Example: numHrznPts=30

Close path using first and last waypoints — Option to close path using first and last waypoints

on (default) | off

Option to close the path using the first and last waypoints.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

To get the block parameter value programmatically, use the get_param function.

Parameter:	pathClosed
Values:	on (default) | off
Data Types:	char | string

Example: pathClosed="off"

Output an array of the search path horizon — Option to output array of search path horizon

off (default) | on

Option to output an array of the search path horizon.

Tunable: Yes

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

To get the block parameter value programmatically, use the get_param function.

Parameter:	multiPoints
Values:	off (default) | on
Data Types:	char | string

Example: multiPoints="on"

Sample rate, dt [s] — Sample rate

0.01 (default) | -1 | positive scalar

Sample rate, in s.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

To get the block parameter value programmatically, use the get_param function.

Parameter:	dt
Values:	0.01 (default) | -1 | positive scalar
Data Types:	single | double

Example: dt=0.02

Plot path and curvature — Option to plot path and curvature

button

Option to plot the path and curvature.

Extended Capabilities

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

Version History

Introduced in R2026a