Reference Path Generator

R2026b

Generate vehicle reference pose and path curvatures

Since R2026a

• 

Reference Path Generator block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

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. It then 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. Optionally, you can specify a vehicle reference using reference path waypoints and instantaneous vehicle position.

The figure shows how the Reference Path Generator block generates the reference horizon from the fitted path. Blue circles represent the specified waypoints or a RoadRunner scenario object, Reference path waypoints [m, rad] or RoadRunner Scenario object, connected by a smooth clothoid curve. From the current vehicle position and orientation specified by the block inputs, X, Y, and psi, the block identifies the nearest point on the path. It then 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, providing a continuous horizon.

Examples

Generate Constant Velocity Reference Path with Handling Limits

Use the Reference Path Generator block to generate a constant velocity reference for a path-following simulation.

• Open Live Script

Use RoadRunner Scenario Object as Reference Oval Path

Use Reference Path Generator block to simulate vehicle that follows a RoadRunner scenario object.

• Open Live Script

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. The block uses this input to verify that the vehicle has reached the XGate location to start 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. The block uses this input to generate an appropriate reference pose.

Data Types: single | double

psi — Vehicle yaw angle

scalar

Vehicle yaw angle with respect to the global coordinate system. The block uses this input 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

Reference path waypoints [m, rad] or RoadRunner Scenario object — Reference path

n-by-3 array (default) | n-by-3 array | scenario object

Reference path that the block uses to generate vehicle reference pose, curvature, and optional velocity signals. You can specify the reference path as either:

• Numeric waypoints defined in workspace variables

• A RoadRunner scenario object

Type	Data Description
Numeric waypoints	Reference path waypoints, specified as an n-by-2 array where n is the number of waypoints, in m. Optionally, you can specify a third column in the array of path tangent angles, in rad, which the block enforces during the fitting process. Specifying this third column can lead to more precise and consistent fitting.
In R2026b: RoadRunner objects	RoadRunner scenario object, including: roadrunnerAPI (RoadRunner Scenario) Route (RoadRunner Scenario) Vehicle (RoadRunner Scenario) Scenario (RoadRunner Scenario)

Note

To get a good path fit, 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

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"

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"

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

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

Reference Velocity

Velocity reference — Velocity reference

None (default) | Constant | Waypoint

Since R2026b

Set a velocity reference for the vehicle as it follows the generated path.

Parameter	Setting	Description
Velocity reference	None	No specified reference velocity. If you want the vehicle to have a target velocity as it follows the path, you must modify the model.
	Constant	As it follows the path, the vehicle uses the constant target velocity specified by the Nominal reference velocity parameter.
	Waypoint	As it follows the path, the vehicle uses the target velocity specified by the Nominal reference velocity parameter. The value is a velocity array of the same dimensions specified in Reference path waypoints, refPathXY. Along the path between the waypoints, the block interpolates the reference velocity.

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:	velRefMode
Values:	None (default) | Constant | Waypoint

Nominal reference velocity or RoadRunner Scenario object, velRef [velRefUnit] — Nominal reference velocity

200 (default) | [0, inf)

Since R2026b

Nominal reference velocity, specified in the units set by the Reference velocity unit, velRefUnit parameter.

• If Velocity reference is set to Constant, then this value is scalar.

• If Velocity reference is set to Waypoint, then this value is reference path waypoints specified as an n-by-3 array, where n is the number of waypoints.

Dependencies

To enable this parameter, set Velocity reference to either Constant or Waypoint.

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:	velRef
Values:	20 (default) | [0, inf)
Data Types:	single | double

Example: velRef=240

Reference velocity unit, velRefUnit [] — Velocity unit

mph (default) | m/s | km/hr

Since R2026b

Nominal reference velocity unit.

Dependencies

To enable this parameter, set Velocity reference to either Constant or Waypoint.

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:	velRefUnit
Values:	m/s (default)
Data Types:	char | string

Example: velRefUnit="km/hr"

Enable curvature-based constraints — Option to constrain reference velocity

off (default) | on

Since R2026b

Option to constrain the reference velocity.

Dependencies

To enable this parameter, set Velocity reference to either Constant or Waypoint.

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

Example: accelLimGroup="on"

Minimum velocity reference, velRefMin — Minimum reference velocity

0 (default) | scalar in the range (-inf, velRefMax)

Since R2026b

Minimum reference velocity, in the units specified by the Reference velocity unit, velRefUnit parameter.

The block does support reverse driving for vehicles without a trailer. If you do specify a minimum reference velocity less than 0:

• A reasonable Reference velocity unit, velRefUnit is -20 mph.

• Carefully tune the Stanley Driver reverse gain.

reseasonable lower limit is -20 mph. Carefully duen the

Dependencies

To enable this parameter, set Velocity reference to either Constant or Waypoint.

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:	velRefMin
Values:	0 (default) | scalar in the range [0, velRefMax)
Data Types:	single | double

Example: velRefMin=10

Maximum velocity reference, velRefMax — Maximum reference velocity

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

Since R2026b

Maximum reference velocity, in the units specified by the Reference velocity unit, velRefUnit parameter.

Dependencies

Enabled when Enable curvature-based constraints is set to on and Velocity reference is set to either:

• Constant

• Waypoint

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:	velRefMax
Values:	250 (default) | scalar in the range (0, inf)
Data Types:	single | double

Example: velRefMax=60

Lateral acceleration limit, ayMax [g] — Lateral acceleration limit

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

Since R2026b

Lateral acceleration limit, in g.

Dependencies

Enabled when Enable curvature-based constraints is set to on and Velocity reference is set to either:

• Constant

• Waypoint

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:	ayMax
Values:	1.2 (default) | scalar in the range (0, inf)
Data Types:	single | double

Example: ayMax=1.1

Braking deceleration limit, axMin [g] — Braking deceleration limit

-0.9 (default) | scalar in the range (-inf,0)

Since R2026b

Braking deceleration limit, in g.

Dependencies

Enabled when Enable curvature-based constraints is set to on and Velocity reference is set to either:

• Constant

• Waypoint

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:	axMin
Values:	-0.9 (default) | scalar in the range (-inf,0)
Data Types:	single | double

Example: axMin=-0.8

Tractive acceleration limit, axMax — Tractive acceleration limit

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

Since R2026b

Tractive acceleration limit, in g.

Dependencies

Enabled when Enable curvature-based constraints is set to on and Velocity reference is set to either:

• Constant

• Waypoint

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:	axMax
Values:	0.30 (default) | scalar in the range (0, inf)
Data Types:	single | double

Example: axMax=0.25

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.

Version History

Introduced in R2026a

R2026b: Import RoadRunner scenarios as reference path

To simplify the workflow for using a RoadRunner object as the reference path in Vehicle Dynamics Blockset™ simulations, directly import scenarios into the Reference Path Generator block. Set the Reference path waypoints [m, rad] or RoadRunner Scenario object parameter to a RoadRunner object, including routes, actors, or scenarios.

Prior to R2026b, the Reference path waypoints [m, rad] or RoadRunner Scenario object parameter was named Reference path waypoints, refPathXY [m] . You could only specify reference path waypoints.

R2026b: Set reference velocity as vehicle follows reference path

Use new parameters to specify an optional velocity reference as the vehicle follows the reference path. Previously, the block did not allow you to set a reference velocity. For compatibility with models created before R2026b, set Velocity reference to None.

Parameter	Setting	Description
Velocity reference	None	No specified reference velocity. If you want the vehicle to have a target velocity as it follows the path, you must modify the model.
	Constant	As it follows the reference path, the vehicle uses the constant velocity specified by the Nominal reference velocity parameter.
	Waypoint	As it follows the reference path, the vehicle uses the velocity specified by the Nominal reference velocity parameter. The value is an array of the same dimensions specified in Reference path waypoints, refPathXY.

If you set Velocity reference to Constant or Waypoint, you can use these parameters to provide constraints on the reference velocity.

Parameter	Description
Minimum velocity reference, velRefMin	Minimum velocity as vehicle follows path
Maximum velocity reference, velRefMax	Maximum velocity as vehicle follows path
Lateral acceleration limit, ayMax	Lateral acceleration limit as vehicle follows path
Braking deceleration limit, axMin	Braking deceleration limit as vehicle follows path
Tractive acceleration limit, axMax	Longitudinal acceleration limit as vehicle follows path