insAccelerometer

Model accelerometer readings for sensor fusion

Since R2022a

Description

The insAccelerometer object models accelerometer readings for sensor fusion. Passing an insAccelerometer object to an insEKF object enables the insEKF object to fuse accelerometer data. For details on the accelerometer model, see Algorithms.

Creation

Syntax

sensor = insAccelerometer

Description

sensor = insAccelerometer creates an insAccelerometer object. Passing the created sensor to an insEKF object enables the insEKF object to fuse accelerometer data. When fusing data with the fuse object function of insEKF, pass sensor as the second argument to identify the data as obtained from an accelerometer.

Examples

Create insAccelerometer for Use in insEKF

Create two insAccelerometer objects and pass them to an insEKF object.

sensor1 = insAccelerometer;
sensor2 = insAccelerometer;
filterOrientation = insEKF(sensor1,sensor2,insMotionOrientation)

filterOrientation = 
  insEKF with properties:

                   State: [13x1 double]
         StateCovariance: [13x13 double]
    AdditiveProcessNoise: [13x13 double]
             MotionModel: [1x1 insMotionOrientation]
                 Sensors: {[1x1 insAccelerometer]  [1x1 insAccelerometer]}
             SensorNames: {'Accelerometer'  'Accelerometer_1'}
          ReferenceFrame: 'NED'

Since the insMotionOrientation object does not model linear acceleration, the filter does not estimate acceleration.

stateinfo(filterOrientation)

ans = struct with fields:
             Orientation: [1 2 3 4]
         AngularVelocity: [5 6 7]
      Accelerometer_Bias: [8 9 10]
    Accelerometer_1_Bias: [11 12 13]

Create another two insAccelerometer objects and pass them to a new insEKF object. Since the insMotionPose object models linear acceleration, the filter estimates acceleration.

sensor3 = insAccelerometer;
sensor4 = insAccelerometer;

filterPose = insEKF(sensor3,sensor4,insMotionPose)

filterPose = 
  insEKF with properties:

                   State: [22x1 double]
         StateCovariance: [22x22 double]
    AdditiveProcessNoise: [22x22 double]
             MotionModel: [1x1 insMotionPose]
                 Sensors: {[1x1 insAccelerometer]  [1x1 insAccelerometer]}
             SensorNames: {'Accelerometer'  'Accelerometer_1'}
          ReferenceFrame: 'NED'

stateinfo(filterPose)

ans = struct with fields:
             Orientation: [1 2 3 4]
         AngularVelocity: [5 6 7]
                Position: [8 9 10]
                Velocity: [11 12 13]
            Acceleration: [14 15 16]
      Accelerometer_Bias: [17 18 19]
    Accelerometer_1_Bias: [20 21 22]

Fuse a measurement from sensor3.

fuse(filterPose,sensor3,[1 1 1],eye(3))

ans = 22×1

    0.9958
    0.0649
   -0.0649
         0
         0
         0
         0
         0
         0
         0
      ⋮

Algorithms

The insAccelerometer object models the accelerometer reading as acceleration in the sensor frame. Depending on whether the insEKF object estimates linear acceleration in the state equations, the measurement equation takes one of two forms:

• If the insEKF object does not estimate the acceleration state, the measurement equation is:

  $$h(x)=g_{sensor}+\Delta$$

  where h(x) is the three-dimensional measurement output, g_sensor is the gravitational acceleration expressed in the sensor frame, and Δ is the three-dimensional bias of the sensor, modeled as a constant vector in the sensor frame.

• If the insEKF object estimates the acceleration state, the equation is:

  $$h(x)=g_{sensor}+a_{sensor}+\Delta$$

  where a_sensor is the acceleration, excluding the gravity acceleration, expressed in the sensor frame.

Passing an insAccelerometer object to an insEKF filter object enables the filter object to additionally track the bias of the accelerometer. Internally, the insEKF object decides if the acceleration state is estimated by calling its stateparts object function.

Version History

Introduced in R2022a