perturb

Apply perturbations to object

Syntax

offsets = perturb(obj)

Description

offsets = perturb(obj) applies the perturbations defined on the object, obj and returns the offset values. You can define perturbations on the object by using the perturbations function.

Examples

Perturb Waypoint Trajectory

Define a waypoint trajectory. By default, this trajectory contains two waypoints.

traj = waypointTrajectory

traj = 
  waypointTrajectory with properties:

         SampleRate: 100
    SamplesPerFrame: 1
          Waypoints: [2×3 double]
      TimeOfArrival: [2×1 double]
         Velocities: [2×3 double]
             Course: [2×1 double]
        GroundSpeed: [2×1 double]
          ClimbRate: [2×1 double]
        Orientation: [2×1 quaternion]
          AutoPitch: 0
           AutoBank: 0
     ReferenceFrame: 'NED'

Define perturbations on the Waypoints property and the TimeOfArrival property.

rng(2020);
perturbs1 = perturbations(traj,'Waypoints','Normal',1,1)

perturbs1=2×3 table
       Property          Type            Value       
    _______________    ________    __________________

    "Waypoints"        "Normal"    {[  1]}    {[  1]}
    "TimeOfArrival"    "None"      {[NaN]}    {[NaN]}

perturbs2 = perturbations(traj,'TimeOfArrival','Selection',{[0;1],[0;2]})

perturbs2=2×3 table
       Property           Type                     Value             
    _______________    ___________    _______________________________

    "Waypoints"        "Normal"       {[     1]}    {[            1]}
    "TimeOfArrival"    "Selection"    {1×2 cell}    {[0.5000 0.5000]}

Perturb the trajectory.

offsets = perturb(traj)

offsets=2×1 struct array with fields:
    Property
    Offset
    PerturbedValue

The Waypoints property and the TimeOfArrival property have changed.

traj.Waypoints

ans = 2×3

    1.8674    1.0203    0.7032
    2.3154   -0.3207    0.0999

traj.TimeOfArrival

ans = 2×1

     0
     2

Perturb Accuracy of insSensor

Create an insSensor object.

sensor = insSensor

sensor = 
  insSensor with properties:

           MountingLocation: [0 0 0]            m    
               RollAccuracy: 0.2                deg  
              PitchAccuracy: 0.2                deg  
                YawAccuracy: 1                  deg  
           PositionAccuracy: [1 1 1]            m    
           VelocityAccuracy: 0.05               m/s  
       AccelerationAccuracy: 0                  m/s² 
    AngularVelocityAccuracy: 0                  deg/s
                  TimeInput: 0                       
               RandomStream: 'Global stream'         

Define the perturbation on the RollAccuracy property as three values with an equal possibility each.

values = {0.1 0.2 0.3}

values=1×3 cell array
    {[0.1000]}    {[0.2000]}    {[0.3000]}

probabilities = [1/3 1/3 1/3]

probabilities = 1×3

    0.3333    0.3333    0.3333

perturbations(sensor,'RollAccuracy','Selection',values,probabilities)

ans=7×3 table
            Property                Type                        Value                 
    _________________________    ___________    ______________________________________

    "RollAccuracy"               "Selection"    {1×3 cell}    {[0.3333 0.3333 0.3333]}
    "PitchAccuracy"              "None"         {[   NaN]}    {[                 NaN]}
    "YawAccuracy"                "None"         {[   NaN]}    {[                 NaN]}
    "PositionAccuracy"           "None"         {[   NaN]}    {[                 NaN]}
    "VelocityAccuracy"           "None"         {[   NaN]}    {[                 NaN]}
    "AccelerationAccuracy"       "None"         {[   NaN]}    {[                 NaN]}
    "AngularVelocityAccuracy"    "None"         {[   NaN]}    {[                 NaN]}

Perturb the sensor object using the perturb function.

rng(2020)
perturb(sensor);
sensor

sensor = 
  insSensor with properties:

           MountingLocation: [0 0 0]            m    
               RollAccuracy: 0.5                deg  
              PitchAccuracy: 0.2                deg  
                YawAccuracy: 1                  deg  
           PositionAccuracy: [1 1 1]            m    
           VelocityAccuracy: 0.05               m/s  
       AccelerationAccuracy: 0                  m/s² 
    AngularVelocityAccuracy: 0                  deg/s
                  TimeInput: 0                       
               RandomStream: 'Global stream'         

The RollAccuracy is perturbed to 0.5 deg.

Perturb imuSensor Parameters

Create an imuSensor object and show its perturbable properties.

imu = imuSensor;
perturbations(imu)

ans=17×3 table
                   Property                    Type           Value       
    ______________________________________    ______    __________________

    "Accelerometer.MeasurementRange"          "None"    {[NaN]}    {[NaN]}
    "Accelerometer.Resolution"                "None"    {[NaN]}    {[NaN]}
    "Accelerometer.ConstantBias"              "None"    {[NaN]}    {[NaN]}
    "Accelerometer.NoiseDensity"              "None"    {[NaN]}    {[NaN]}
    "Accelerometer.BiasInstability"           "None"    {[NaN]}    {[NaN]}
    "Accelerometer.RandomWalk"                "None"    {[NaN]}    {[NaN]}
    "Accelerometer.TemperatureBias"           "None"    {[NaN]}    {[NaN]}
    "Accelerometer.TemperatureScaleFactor"    "None"    {[NaN]}    {[NaN]}
    "Gyroscope.MeasurementRange"              "None"    {[NaN]}    {[NaN]}
    "Gyroscope.Resolution"                    "None"    {[NaN]}    {[NaN]}
    "Gyroscope.ConstantBias"                  "None"    {[NaN]}    {[NaN]}
    "Gyroscope.NoiseDensity"                  "None"    {[NaN]}    {[NaN]}
    "Gyroscope.BiasInstability"               "None"    {[NaN]}    {[NaN]}
    "Gyroscope.RandomWalk"                    "None"    {[NaN]}    {[NaN]}
    "Gyroscope.TemperatureBias"               "None"    {[NaN]}    {[NaN]}
    "Gyroscope.TemperatureScaleFactor"        "None"    {[NaN]}    {[NaN]}
      ⋮

Specify the perturbation for the NoiseDensity property of the accelerometer as a uniform distribution.

perturbations(imu,'Accelerometer.NoiseDensity', ...
    'Uniform',1e-5,1e-3);

Specify the perturbation for the RandomWalk property of the gyroscope as a truncated normal distribution.

 perts = perturbations(imu,'Gyroscope.RandomWalk', ...
    'TruncatedNormal',2,1e-5,0,Inf);

Load prerecorded IMU data.

load imuSensorData.mat 
numSamples = size(orientations);

Simulate the imuSensor three times with different perturbation realizations.

rng(2021); % For repeatable results
numRuns = 3;
colors = ['b' 'r' 'g'];
for idx = 1:numRuns

    % Clone IMU to maintain original values
    imuCopy = clone(imu);

    % Perturb noise values
    offsets = perturb(imuCopy);

    % Obtain the measurements 
    [accelReadings,gyroReadings] = imuCopy(accelerations,angularVelocities,orientations);
    
    % Plot the results
    plot(times,gyroReadings(:,3),colors(idx));
    hold on;
end
xlabel('Time (s)')
ylabel('Z-Component of Gyro Readings (rad/s)')
legend("First Pass","Second Pass","Third Pass");
hold off

Input Arguments

obj — Object for perturbation

object

Object for perturbation, specified as an object. The objects that you can perturb include:

• waypointTrajectory

• geoTrajectory

• kinematicTrajectory

• insSensor

• imuSensor

• radarEmitter

• fusionRadarSensor

• sonarEmitter

• sonarSensor

• irSensor

• monostaticLidarSensor

Output Arguments

offsets — Property offsets

array of structure

Property offsets, returned as an array of structures. Each structure contains these fields:

Field Name	Description
Property	Name of perturbed property
Offset	Offset values applied in the perturbation
PerturbedValue	Property values after the perturbation

Version History

Introduced in R2020b