controllers::PredictiveStanleyController Class Reference

This class implements the Predictive Stanley Controller. This controller is used to follow a path using the Stanley method with predictive control. More...

#include <PredictiveStanleyController.h>

Collaboration diagram for controllers::PredictiveStanleyController:

Classes
struct	DriveVector

Public Member Functions
	PredictiveStanleyController (const double dControlGain=0.1, const double dAngularVelocityLimit=90.0, const int nPredictionHorizon=5, const double dPredictionTimeStep=0.01)
	Construct a new Predictive Stanley Controller:: Predictive Stanley Controller object.
	~PredictiveStanleyController ()
	Destroy the Predictive Stanley Controller:: Predictive Stanley Controller object.
DriveVector	Calculate (const geoops::RoverPose &stCurrentPose, const double dMaxSpeed=constants::NAVIGATING_MOTOR_POWER)
	Calculate an updated steering angle for the rover based on the current pose using the predictive stanley controller.
void	SetReferencePath (const std::vector< geoops::Waypoint > &vReferencePath)
	Sets the path that the controller will follow.
void	SetReferencePath (const std::vector< geoops::UTMCoordinate > &vReferencePath)
	Sets the path that the controller will follow.
void	SetReferencePath (const std::vector< geoops::GPSCoordinate > &vReferencePath)
	Sets the path that the controller will follow.
void	SetControlGain (const double dControlGain)
	Setter for the control gain of the stanley controller.
void	SetAngularVelocityLimit (const double dAngularVelocityLimit)
	Setter for the angular velocity limit of the stanley controller.
std::vector< geoops::Waypoint >	GetReferencePath () const
	Accessor for the reference path that the controller is following.
double	GetControlGain () const
	Accessor for the control gain of the stanley controller.
double	GetAngularVelocityLimit () const
	Accessor for the angular velocity limit of the stanley controller.
double	GetReferencePathTargetIndex () const
	Accessor for the current target index in the reference path.

Private Member Functions
geoops::Waypoint	FindClosestWaypointInPath (const geoops::UTMCoordinate &stCurrentPosition)
	Given the current position of the rover, find the point on the reference path that is closest to the rover's front axle position (based on the wheelbase). This is what makes sure the rover progresses forward in indexes along the path.

Private Attributes
UnicycleModel	m_UnicycleModel
double	m_dControlGain
double	m_dAngularVelocityLimit
int	m_nPredictionHorizon
double	m_dPredictionTimeStep
int	m_nCurrentReferencePathTargetIndex
std::vector< geoops::Waypoint >	m_vReferencePath

Detailed Description

This class implements the Predictive Stanley Controller. This controller is used to follow a path using the Stanley method with predictive control.

Note

See docs/WhitePapers/2020-A-Path-Tracking-Algorithm-Using-Predictive-Stanley-Lateral-Controller.pdf

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

Constructor & Destructor Documentation

PredictiveStanleyController()

controllers::PredictiveStanleyController::PredictiveStanleyController	(	const double	dControlGain = 0.1,
		const double	dAngularVelocityLimit = 90.0,
		const int	nPredictionHorizon = 5,
		const double	dPredictionTimeStep = 0.01
	)

Construct a new Predictive Stanley Controller:: Predictive Stanley Controller object.

Parameters

dControlGain	- The control gain for the controller.
dSteeringAngleLimit	- The maximum steering angle the rover can turn.
nPredictionHorizon	- The number of predictions to make.
dPredictionTimeStep	- The time step to predict the future state. How far into the future to predict.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        // Initialize member variables.
        m_dControlGain                     = dControlGain;
        m_dAngularVelocityLimit            = dAngularVelocityLimit;
        m_nPredictionHorizon               = nPredictionHorizon;
        m_dPredictionTimeStep              = dPredictionTimeStep;
        m_nCurrentReferencePathTargetIndex = 0;
        m_UnicycleModel                    = UnicycleModel(0.0, 0.0, 0.0);
    }

~PredictiveStanleyController()

controllers::PredictiveStanleyController::~PredictiveStanleyController

(

)

Destroy the Predictive Stanley Controller:: Predictive Stanley Controller object.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        // Nothing to do yet.
    }

Member Function Documentation

Calculate()

PredictiveStanleyController::DriveVector controllers::PredictiveStanleyController::Calculate	(	const geoops::RoverPose &	stCurrentPose,
		const double	dMaxSpeed = constants::NAVIGATING_MOTOR_POWER
	)

Calculate an updated steering angle for the rover based on the current pose using the predictive stanley controller.

Parameters

stCurrentPose	- The current pose of the rover.
dMaxSpeed	- The maximum speed the rover can travel.

Returns

double - The new output steering angle for the rover.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        // Create instance variables.
        double dSteeringAngle = 0.0;
        std::vector<UnicycleModel::Prediction> vPredictions;
 
        // Check if the reference path is empty.
        if (m_vReferencePath.empty())
        {
            // Submit logger message.
            LOG_WARNING(logging::g_qSharedLogger, "PredictiveStanleyController::Calculate: Reference path is empty. Cannot calculate drive powers.");
 
            return DriveVector{0.0, 0.0};
        }
 
        // Check if we are at the end of the path. Normally stanley would continue driving in the last direction of the calculated path
        // headings, but we want to make sure we get to the end point, so we'll just drive straight to it once at the end of the path.
        // We check if we are on the last segment (size - 2).
        if (m_nCurrentReferencePathTargetIndex >= static_cast<int>(m_vReferencePath.size()) - 2)
        {
            // Get the start and end points of the last segment.
            geoops::UTMCoordinate stLastPoint         = m_vReferencePath.back().GetUTMCoordinate();
            geoops::UTMCoordinate stSecondToLastPoint = m_vReferencePath[m_vReferencePath.size() - 2].GetUTMCoordinate();
            geoops::UTMCoordinate stRoverPos          = stCurrentPose.GetUTMCoordinate();
 
            // Calculate vector of the last segment (Start -> End).
            double dSegmentX     = stLastPoint.dEasting - stSecondToLastPoint.dEasting;
            double dSegmentY     = stLastPoint.dNorthing - stSecondToLastPoint.dNorthing;
            double dSegmentLenSq = dSegmentX * dSegmentX + dSegmentY * dSegmentY;
 
            // Calculate vector from Segment Start -> Rover.
            double dRoverVectorX = stRoverPos.dEasting - stSecondToLastPoint.dEasting;
            double dRoverVectorY = stRoverPos.dNorthing - stSecondToLastPoint.dNorthing;
 
            // Project rover onto the segment vector with a dot product.
            // t represents the normalized distance along the segment (0.0 = start, 1.0 = end).
            double dNormalDistance = 0.0;
            if (dSegmentLenSq > 1e-6)
            {
                dNormalDistance = (dRoverVectorX * dSegmentX + dRoverVectorY * dSegmentY) / dSegmentLenSq;
            }
 
            // Check if we have passed the end (t >= 1.0) or are very close to it.
            // We add a small tolerance (e.g., 0.99) or strictly check t >= 1.0.
            if (dNormalDistance >= 1.0)
            {
                // We have reached or passed the end.
                // Calculate heading to the last point to ensure we turn around if we overshot.
                double dHeadingToLastWaypoint = geoops::CalculateGeoMeasurement(stRoverPos, stLastPoint).dStartRelativeBearing;
                return DriveVector{dHeadingToLastWaypoint, 1.0};
            }
        }
 
        // Update the unicycle model with the current state.
        m_UnicycleModel.UpdateState(stCurrentPose.GetUTMCoordinate().dEasting, stCurrentPose.GetUTMCoordinate().dNorthing, stCurrentPose.GetCompassHeading());
        // Predict the future state of the model.
        m_UnicycleModel.Predict(m_dPredictionTimeStep, m_nPredictionHorizon, vPredictions);
 
        // Loop through all the predicted future states to compute the steering angle.
        for (size_t nIter = 0; nIter < vPredictions.size(); ++nIter)
        {
            // Create instance variables.
            double dPredictedXPosition = vPredictions[nIter].dXPosition;
            double dPredictedYPosition = vPredictions[nIter].dYPosition;
            double dPredictedTheta     = vPredictions[nIter].dTheta;
 
            // Create a UTM coordinate for the predicted position.
            geoops::UTMCoordinate stPredictedPosition = stCurrentPose.GetUTMCoordinate();
            stPredictedPosition.dEasting              = dPredictedXPosition;
            stPredictedPosition.dNorthing             = dPredictedYPosition;
            // Find the closest point to the reference path.
            geoops::Waypoint stClosestWaypoint = FindClosestWaypointInPath(stPredictedPosition);
 
            // Compute the path forward vector from the segment start -> next waypoint (use index set by FindClosestWaypointInPath).
            int nIdx                                    = m_nCurrentReferencePathTargetIndex;
            int nNextIdx                                = std::min(nIdx + 1, static_cast<int>(m_vReferencePath.size() - 1));
            const geoops::UTMCoordinate& stSegmentStart = m_vReferencePath[nIdx].GetUTMCoordinate();
            const geoops::UTMCoordinate& stSegmentEnd   = m_vReferencePath[nNextIdx].GetUTMCoordinate();
 
            // Forward vector of the path segment.
            double dForwardVectorX = stSegmentEnd.dEasting - stSegmentStart.dEasting;
            double dForwardVectorY = stSegmentEnd.dNorthing - stSegmentStart.dNorthing;
            double dForwardNorm    = std::hypot(dForwardVectorX, dForwardVectorY);
            // Degenerate segment. Skip this prediction step.
            if (dForwardNorm < 1e-9)
            {
                continue;
            }
 
            // Unit forward vector.
            double dFwdUnitX = dForwardVectorX / dForwardNorm;
            double dFwdUnitY = dForwardVectorY / dForwardNorm;
            // Math angle of segment (atan2 gives angle from +X (East), CCW positive) in degrees.
            double dSegmentMathDeg = std::atan2(dForwardVectorY, dForwardVectorX) * (180.0 / M_PI);
            // Convert math angle to COMPASS heading (0 = North, clockwise positive):
            // compass = (90 - math) mod 360.
            double dPathHeadingDeg = std::fmod(90.0 - dSegmentMathDeg + 360.0, 360.0);
            // Predicted theta is produced by UnicycleModel in DEGREES (compass). Treat as degrees.
            double dPredThetaDeg = dPredictedTheta;
            // Small helper: signed smallest-angle difference in degrees in (-180, 180].
            std::function<double(double, double)> AngleDiffDeg = [](double targetDeg, double sourceDeg) -> double
            {
                double diff = std::fmod(targetDeg - sourceDeg + 540.0, 360.0) - 180.0;
                return diff;
            };
            // Heading error (degrees): positive means we should rotate clockwise to match target (compass conv).
            double dHeadingError = AngleDiffDeg(dPathHeadingDeg, dPredThetaDeg);
 
            // Vehicle vector relative to the closest point. (projection)
            double dVehicleVectorX = dPredictedXPosition - stClosestWaypoint.GetUTMCoordinate().dEasting;
            double dVehicleVectorY = dPredictedYPosition - stClosestWaypoint.GetUTMCoordinate().dNorthing;
            // Longitudinal projection and lateral vector.
            double dLongitudinal    = dVehicleVectorX * dFwdUnitX + dVehicleVectorY * dFwdUnitY;
            double dLateralX        = dVehicleVectorX - dLongitudinal * dFwdUnitX;
            double dLateralY        = dVehicleVectorY - dLongitudinal * dFwdUnitY;
            double dLateralDistance = std::hypot(dLateralX, dLateralY);
            // Sign using cross product. (left positive)
            double dCross           = dFwdUnitX * dVehicleVectorY - dFwdUnitY * dVehicleVectorX;
            double dCrossTrackError = (dCross > 0.0 ? 1.0 : -1.0) * dLateralDistance;    // meters
 
            // Apply an exponential weight factor that decreases as we predict further into the future.
            double dTimeWeight = std::exp(-1.5 * static_cast<double>(nIter));
 
            // Use model velocity if available, otherwise fall back to provided dMaxSpeed
            double dModelSpeed = m_UnicycleModel.GetVelocity();
            double dSpeed      = (dModelSpeed > 0.0) ? dModelSpeed : dMaxSpeed;
            dSpeed             = std::max(dSpeed, 1e-4);
 
            // Stanley control law to compute the steering angle.
            double dStanleyTermRad = std::atan2(m_dControlGain * dCrossTrackError, dSpeed);
            double dStanleyTermDeg = dStanleyTermRad * (180.0 / M_PI);
            // Combine the heading error and the stanley term.
            dSteeringAngle += (dStanleyTermDeg + dHeadingError) * dTimeWeight;
 
            // Limit the steering angle to the given limit.
            dSteeringAngle = std::clamp(dSteeringAngle, -m_dAngularVelocityLimit, m_dAngularVelocityLimit);
        }
 
        // The new steering heading must be from 0-360 degrees.
        double dAbsoluteHeadingGoal = numops::InputAngleModulus(stCurrentPose.GetCompassHeading() + dSteeringAngle, 0.0, 360.0);
 
        return DriveVector{dAbsoluteHeadingGoal, dMaxSpeed};
    }

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SetReferencePath() [1/3]

void controllers::PredictiveStanleyController::SetReferencePath

(

const std::vector< geoops::Waypoint > &

vReferencePath

)

Sets the path that the controller will follow.

Parameters

vReferencePath

- A reference to a vector of waypoints that make up the path.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        // Reset the current target index.
        m_nCurrentReferencePathTargetIndex = 0;
        // Reset the bicycle model.
        m_UnicycleModel.ResetState();
 
        // Smooth the path by fitting it to a B-spline.
        std::vector<geoops::Waypoint> vSmoothedPath = pathplanners::postprocessing::FitPathWithBSpline(vReferencePath);
 
        // Set the reference path.
        m_vReferencePath = vSmoothedPath;
    }

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SetReferencePath() [2/3]

void controllers::PredictiveStanleyController::SetReferencePath

(

const std::vector< geoops::UTMCoordinate > &

vReferencePath

)

Sets the path that the controller will follow.

Parameters

vReferencePath

- A reference to a vector of UTM coordinates that make up the path.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        // Convert UTM coordinates to waypoints.
        std::vector<geoops::Waypoint> vConvertedPath;
        for (const geoops::UTMCoordinate& stUTMCoord : vReferencePath)
        {
            vConvertedPath.emplace_back(geoops::Waypoint(stUTMCoord, geoops::WaypointType::eNavigationWaypoint, 0.0, -1));
        }
 
        // Set the reference path.
        this->SetReferencePath(vConvertedPath);
    }

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SetReferencePath() [3/3]

void controllers::PredictiveStanleyController::SetReferencePath

(

const std::vector< geoops::GPSCoordinate > &

vReferencePath

)

Sets the path that the controller will follow.

Parameters

vReferencePath

- A reference to a vector of GPS coordinates that make up the path.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        // Convert GPS coordinates to waypoints.
        std::vector<geoops::Waypoint> vConvertedPath;
        for (const geoops::GPSCoordinate& stGPSCoord : vReferencePath)
        {
            vConvertedPath.emplace_back(geoops::Waypoint(stGPSCoord, geoops::WaypointType::eNavigationWaypoint, 0.0, -1));
        }
 
        // Set the reference path.
        this->SetReferencePath(vConvertedPath);
    }

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SetControlGain()

void controllers::PredictiveStanleyController::SetControlGain

(

const double

dControlGain

)

Setter for the control gain of the stanley controller.

Parameters

dControlGain

- The control gain for the controller.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        m_dControlGain = dControlGain;
    }

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SetAngularVelocityLimit()

void controllers::PredictiveStanleyController::SetAngularVelocityLimit

(

const double

dAngularVelocityLimit

)

Setter for the angular velocity limit of the stanley controller.

Parameters

dAngularVelocityLimit

- The angular velocity limit for the controller.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-11

    {
        m_dAngularVelocityLimit = dAngularVelocityLimit;
    }

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GetReferencePath()

std::vector< geoops::Waypoint > controllers::PredictiveStanleyController::GetReferencePath

(

)

const

Accessor for the reference path that the controller is following.

Returns

std::vector<geoops::Waypoint> - A copy of the reference path.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        return m_vReferencePath;
    }

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GetControlGain()

double controllers::PredictiveStanleyController::GetControlGain

(

)

const

Accessor for the control gain of the stanley controller.

Returns

double - The control gain for the controller.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        return m_dControlGain;
    }

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GetAngularVelocityLimit()

double controllers::PredictiveStanleyController::GetAngularVelocityLimit

(

)

const

Accessor for the angular velocity limit of the stanley controller.

Returns

double - The angular velocity limit for the controller.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-11

    {
        return m_dAngularVelocityLimit;
    }

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GetReferencePathTargetIndex()

double controllers::PredictiveStanleyController::GetReferencePathTargetIndex

(

)

const

Accessor for the current target index in the reference path.

Returns

double - The current target index in the reference path.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        return m_nCurrentReferencePathTargetIndex;
    }

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FindClosestWaypointInPath()

geoops::Waypoint controllers::PredictiveStanleyController::FindClosestWaypointInPath ( const geoops::UTMCoordinate &  stCurrentPosition )

private

Given the current position of the rover, find the point on the reference path that is closest to the rover's front axle position (based on the wheelbase). This is what makes sure the rover progresses forward in indexes along the path.

Parameters

stCurrentPosition	- The current position of the rover.
dCurrentHeading	- The current heading of the rover in degrees from 0-360.

Author

clayjay3 (clayt.nosp@m.onra.nosp@m.ycowe.nosp@m.n@gm.nosp@m.ail.c.nosp@m.om)

Date

2025-01-10

    {
        // Create instance variables.
        geoops::Waypoint stClosestWaypoint;
        double dClosestDistanceSq = std::numeric_limits<double>::max();
        const size_t nWaypoints   = m_vReferencePath.size();
 
        // Check for empty path.
        if (nWaypoints == 0)
        {
            return stClosestWaypoint;
        }
 
        // If only a single waypoint, return it directly.
        if (nWaypoints == 1)
        {
            m_nCurrentReferencePathTargetIndex = 0;
            return m_vReferencePath.front();
        }
 
        // We'll search across path segments (i -> i+1) and compute the closest point on each segment.
        int nBestSegmentIndex = -1;
        geoops::UTMCoordinate stBestProjection;
 
        for (size_t siIter = m_nCurrentReferencePathTargetIndex; siIter < nWaypoints - 1; ++siIter)
        {
            const geoops::UTMCoordinate& stA = m_vReferencePath[siIter].GetUTMCoordinate();
            const geoops::UTMCoordinate& stB = m_vReferencePath[siIter + 1].GetUTMCoordinate();
 
            // Segment vector. (B - A)
            double dSX = stB.dEasting - stA.dEasting;
            double dSY = stB.dNorthing - stA.dNorthing;
 
            // Vector from A -> P.
            double dPX                   = stCurrentPosition.dEasting - stA.dEasting;
            double dPY                   = stCurrentPosition.dNorthing - stA.dNorthing;
 
            double sSegmentLengthSquared = dSX * dSX + dSY * dSY;
            double dProjT                = 0.0;
            if (sSegmentLengthSquared > 0.0)
            {
                // projection parameter t = dot(P-A, B-A) / |B-A|^2.
                dProjT = (dPX * dSX + dPY * dSY) / sSegmentLengthSquared;
                dProjT = std::clamp(dProjT, 0.0, 1.0);
            }
            else
            {
                // Degenerate segment (A == B). Use A as projection.
                dProjT = 0.0;
            }
 
            // Projection point coordinates.
            double dProjX = stA.dEasting + dProjT * dSX;
            double dProjY = stA.dNorthing + dProjT * dSY;
 
            // Squared distance from P to projection.
            double dx     = stCurrentPosition.dEasting - dProjX;
            double dy     = stCurrentPosition.dNorthing - dProjY;
            double distSq = dx * dx + dy * dy;
 
            if (distSq < dClosestDistanceSq)
            {
                dClosestDistanceSq                         = distSq;
                nBestSegmentIndex                          = static_cast<int>(siIter);
                stBestProjection.dEasting                  = dProjX;
                stBestProjection.dNorthing                 = dProjY;
                stBestProjection.nZone                     = stA.nZone;
                stBestProjection.bWithinNorthernHemisphere = stA.bWithinNorthernHemisphere;
            }
        }
 
        // If we didn't find a segment (shouldn't happen), fall back to the closest waypoint vertex search.
        if (nBestSegmentIndex < 0)
        {
            double dClosestDist = std::numeric_limits<double>::max();
            for (size_t siIter = 0; siIter < nWaypoints; ++siIter)
            {
                double dDistance = geoops::CalculateGeoMeasurement(stCurrentPosition, m_vReferencePath[siIter].GetUTMCoordinate()).dDistanceMeters;
                if (dDistance < dClosestDist)
                {
                    dClosestDist                       = dDistance;
                    stClosestWaypoint                  = m_vReferencePath[siIter];
                    m_nCurrentReferencePathTargetIndex = static_cast<int>(siIter);
                }
            }
            return stClosestWaypoint;
        }
 
        // Build a waypoint for the projected point.
        // Use the properties of the segment start waypoint as a base, then set the UTM to the projection.
        geoops::Waypoint stSegmentStart   = m_vReferencePath[nBestSegmentIndex];
        geoops::UTMCoordinate stBestCoord = geoops::UTMCoordinate(stBestProjection.dEasting,
                                                                  stBestProjection.dNorthing,
                                                                  stBestProjection.nZone,
                                                                  stBestProjection.bWithinNorthernHemisphere,
                                                                  stSegmentStart.GetUTMCoordinate().dAltitude,
                                                                  stSegmentStart.GetUTMCoordinate().d2DAccuracy,
                                                                  stSegmentStart.GetUTMCoordinate().d3DAccuracy,
                                                                  stSegmentStart.GetUTMCoordinate().dMeridianConvergence,
                                                                  stSegmentStart.GetUTMCoordinate().dScale,
                                                                  stSegmentStart.GetUTMCoordinate().eCoordinateAccuracyFixType,
                                                                  stSegmentStart.GetUTMCoordinate().bIsDifferential);
        stClosestWaypoint                 = geoops::Waypoint(stBestCoord);
 
        // Update the controller's current reference index to the segment start index so callers can use (index + 1).
        m_nCurrentReferencePathTargetIndex = nBestSegmentIndex;
 
        return stClosestWaypoint;
    }

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---

The documentation for this class was generated from the following files:

• src/algorithms/controllers/PredictiveStanleyController.h
• src/algorithms/controllers/PredictiveStanleyController.cpp