insSensor

Inertial navigation and GPS simulation model

Description

The insSensor System object™ models data output from an inertial navigation and GPS.

To model output from an inertial navigation and GPS:

1. Create the insSensor object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?.

Creation

Syntax

INS = insSensor

INS = insSensor(Name,Value)

Description

INS = insSensor returns a System object, INS, that models an inertial navigation and GPS reading based on an inertial input signal.

INS = insSensor(Name,Value) sets each property Name to the specified Value. Unspecified properties have default values.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

RollAccuracy — Accuracy of roll measurement (deg)

0.2 (default) | nonnegative real scalar

Accuracy of the roll measurement of the sensor body in degrees, specified as a nonnegative real scalar.

Roll is defined as rotation around the x-axis of the sensor body. Roll noise is modeled as a white noise process. RollAccuracy sets the standard deviation, in degrees, of the roll measurement noise.

Tunable: Yes

Data Types: single | double

PitchAccuracy — Accuracy of pitch measurement (deg)

0.2 (default) | nonnegative real scalar

Accuracy of the pitch measurement of the sensor body in degrees, specified as a nonnegative real scalar.

Pitch is defined as rotation around the y-axis of the sensor body. Pitch noise is modeled as a white noise process. PitchAccuracy defines the standard deviation, in degrees, of the pitch measurement noise.

Tunable: Yes

Data Types: single | double

YawAccuracy — Accuracy of yaw measurement (deg)

1 (default) | nonnegative real scalar

Accuracy of the yaw measurement of the sensor body in degrees, specified as a nonnegative real scalar.

Yaw is defined as rotation around the z-axis of the sensor body. Yaw noise is modeled as a white noise process. YawAccuracy defines the standard deviation, in degrees, of the yaw measurement noise.

Tunable: Yes

Data Types: single | double

PositionAccuracy — Accuracy of position measurement (m)

1 (default) | nonnegative real scalar

Accuracy of the position measurement of the sensor body in meters, specified as a nonnegative real scalar.

Position noise is modeled as a white noise process. PositionAccuracy defines the standard deviation, in meters, of the position measurement noise.

Tunable: Yes

Data Types: single | double

VelocityAccuracy — Accuracy of velocity measurement (m/s)

0.05 (default) | nonnegative real scalar

Accuracy of the velocity measurement of the sensor body in meters per second, specified as a nonnegative real scalar.

Velocity noise is modeled as a white noise process. VelocityAccuracy defines the standard deviation, in meters per second, of the velocity measurement noise.

Tunable: Yes

Data Types: single | double

RandomStream — Random number source

'Global stream' (default) | 'mt19937ar with seed'

Random number source, specified as a character vector:

• 'Global stream' –– Random numbers are generated using the current global random number stream.

• 'mt19937ar with seed' –– Random numbers are generated using the mt19937ar algorithm with the seed specified by the Seed property.

Data Types: char | string

Seed — Initial seed

67 (default) | nonnegative integer scalar

Initial seed of an mt19937ar random number generator algorithm, specified as a real, nonnegative integer scalar.

Dependencies

To enable this property, set RandomStream to 'mt19937ar with seed'.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Usage

Syntax

measurement = INS(motion)

Description

measurement = INS(motion) models the data received from an inertial navigation and GPS reading. The measurement is based on the input signal, motion.

Input Arguments

motion — Ground-truth sensor body motion in local NED

struct

motion is a struct with the following fields:

• 'Position' –– Position of the sensor body in the local NED coordinate system specified as a real finite N-by-3 array in meters. N is the number of samples in the current frame.

• 'Velocity' –– Velocity of the sensor body in the local NED coordinate system specified as a real finite N-by-3 array in meters per second. N is the number of samples in the current frame.

• 'Orientation' –– Orientation of the sensor body with respect to the local NED coordinate system specified as a quaternion N-element column vector or a single or double 3-by-3-by-N rotation matrix. Each quaternion or rotation matrix is a frame rotation from the local NED coordinate system to the current sensor body coordinate system. N is the number of samples in the current frame.

Example: motion = struct('Position',[0,0,0],'Velocity',[0,0,0],'Orientation',quaternion([1,0,0,0]))

Output Arguments

measurement — Measurement of sensor body motion in local NED

struct

measurement is a struct with the following fields:

• 'Position' –– Position measurement of the sensor body in the local NED coordinate system specified as a real finite N-by-3 array in meters. N is the number of samples in the current frame.

• 'Velocity' –– Velocity measurement of the sensor body in the local NED coordinate system specified as a real finite N-by-3 array in meters per second. N is the number of samples in the current frame.

• 'Orientation' –– Orientation measurement of the sensor body with respect to the local NED coordinate system specified as a quaternion N-element column vector or a single or double 3-by-3-by-N rotation matrix. Each quaternion or rotation matrix is a frame rotation from the local NED coordinate system to the current sensor body coordinate system. N is the number of samples in the current frame.

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Specific to insSensor

perturbations	Perturbation defined on object
perturb	Apply perturbations to object

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
reset	Reset internal states of System object

Examples

Generate INS Measurements from Stationary Input

Create a motion struct that defines a stationary position at the local NED origin. Because the platform is stationary, you only need to define a single sample. Assume the ground-truth motion is sampled for 10 seconds with a 100 Hz sample rate. Create a default insSensor System object™. Preallocate variables to hold output from the insSensor object.

Fs = 100;
duration = 10;
numSamples = Fs*duration;

motion = struct( ...
    'Position', zeros(1,3), ...
    'Velocity', zeros(1,3), ...
    'Orientation', ones(1,1,'quaternion'));

INS = insSensor;

positionMeasurements = zeros(numSamples,3);
velocityMeasurements = zeros(numSamples,3);
orientationMeasurements = zeros(numSamples,1,'quaternion');

In a loop, call INS with the stationary motion struct to return the position, velocity, and orientation measurements in the local NED coordinate system. Log the position, velocity, and orientation measurements.

for i = 1:numSamples
    
    measurements = INS(motion);
    
    positionMeasurements(i,:) = measurements.Position;
    velocityMeasurements(i,:) = measurements.Velocity;
    orientationMeasurements(i) = measurements.Orientation;
    
end

Convert the orientation from quaternions to Euler angles for visualization purposes. Plot the position, velocity, and orientation measurements over time.

orientationMeasurements = eulerd(orientationMeasurements,'ZYX','frame');

t = (0:(numSamples-1))/Fs;

subplot(3,1,1)
plot(t,positionMeasurements)
title('Position')
xlabel('Time (s)')
ylabel('Position (m)')
legend('North','East','Down')

subplot(3,1,2)
plot(t,velocityMeasurements)
title('Velocity')
xlabel('Time (s)')
ylabel('Velocity (m/s)')
legend('North','East','Down')

subplot(3,1,3)
plot(t,orientationMeasurements)
title('Orientation')
xlabel('Time (s)')
ylabel('Rotation (degrees)')
legend('Roll', 'Pitch', 'Yaw')

Generate INS Measurements for a Scenario

Generate INS measurements using the insSensor System object™. Use waypointTrajectory to generate the ground-truth path. Use trackingScenario to organize the simulation and visualize the motion.

Specify the ground-truth trajectory as a figure-eight path in the North-East plane. Use a 50 Hz sample rate and 5 second duration.

Fs = 50;
duration = 5;
numSamples = Fs*duration;
t = (0:(numSamples-1)).'/Fs;

a = 2;

x = a.*sqrt(2).*cos(t) ./ (sin(t).^2 + 1);
y = sin(t) .* x;
z = zeros(numSamples,1);

waypoints = [x,y,z];

path = waypointTrajectory('Waypoints',waypoints,'TimeOfArrival',t);

Create an insSensor System object to model receiving INS data. Set the PositionAccuracy to 0.1.

ins = insSensor('PositionAccuracy',0.1);

Create a tracking scenario with a single platform whose motion is defined by path.

scenario = trackingScenario('UpdateRate',Fs);
quadcopter = platform(scenario);
quadcopter.Trajectory = path;

Create a theater plot to visualize the ground-truth quadcopter motion and the quadcopter motion measurements modeled by insSensor.

tp = theaterPlot('XLimits',[-3, 3],'YLimits', [-3, 3]);
quadPlotter = platformPlotter(tp, ...
    'DisplayName', 'Ground-Truth Motion', ...
    'Marker', 's', ...
    'MarkerFaceColor','blue');
insPlotter = detectionPlotter(tp, ...
    'DisplayName','INS Measurement', ...
    'Marker','d', ...
    'MarkerFaceColor','red');

In a loop, advance the scenario until it is complete. For each time step, get the current motion sample, model INS measurements for the motion, and then plot the result.

while advance(scenario)
    motion = platformPoses(scenario,'quaternion');
    
    insMeas = ins(motion);
    
    plotPlatform(quadPlotter,motion.Position);
    plotDetection(insPlotter,insMeas.Position);
    
    pause(1/scenario.UpdateRate)
end

Generate INS Measurements for a Turning Platform

Generate INS measurements using the insSensor System object™. Use waypointTrajectory to generate the ground-truth path.

Specify a ground-truth orientation that begins with the sensor body x-axis aligned with North and ends with the sensor body x-axis aligned with East. Specify waypoints for an arc trajectory and a time-of-arrival vector for the corresponding waypoints. Use a 100 Hz sample rate. Create a waypointTrajectory System object with the waypoint constraints, and set SamplesPerFrame so that the entire trajectory is output with one call.

eulerAngles = [0,0,0; ...
               0,0,0; ...
               90,0,0; ...
               90,0,0];
orientation = quaternion(eulerAngles,'eulerd','ZYX','frame');

r = 20;
waypoints = [0,0,0; ...
             100,0,0; ...
             100+r,r,0; ...
             100+r,100+r,0];

toa = [0,10,10+(2*pi*r/4),20+(2*pi*r/4)];

Fs = 100;
numSamples = floor(Fs*toa(end));

path = waypointTrajectory('Waypoints',waypoints, ...
    'TimeOfArrival',toa, ...
    'Orientation',orientation, ...
    'SampleRate',Fs, ...
    'SamplesPerFrame',numSamples);

Create an insSensor System object to model receiving INS data. Set the PositionAccuracy to 0.1.

ins = insSensor('PositionAccuracy',0.1);

Call the waypoint trajectory object, path, to generate the ground-truth motion. Call the INS simulator, ins, with the ground-truth motion to generate INS measurements.

[motion.Position,motion.Orientation,motion.Velocity] = path();
insMeas = ins(motion);

Convert the orientation returned by ins to Euler angles in degrees for visualization purposes. Plot the full path and orientation over time.

orientationMeasurementEuler = eulerd(insMeas.Orientation,'ZYX','frame');

subplot(2,1,1)
plot(insMeas.Position(:,1),insMeas.Position(:,2));
title('Path')
xlabel('North (m)')
ylabel('East (m)')

subplot(2,1,2)
t = (0:(numSamples-1)).'/Fs;
plot(t,orientationMeasurementEuler(:,1), ...
     t,orientationMeasurementEuler(:,2), ...
     t,orientationMeasurementEuler(:,3));
title('Orientation')
legend('Yaw','Pitch','Roll')
xlabel('Time (s)')
ylabel('Rotation (degrees)')

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

See System Objects in MATLAB Code Generation (MATLAB Coder).