# measurement

## Description

returns the measurement `z`

= measurement(`sensor`

,`filter`

)`z`

from the state maintained in the filter
object. You must implement this method when you define a sensor object based on the `positioning.INSSensorModel`

abstract class.

## Examples

### Customize Sensor Model Used with `insEKF`

Customize a sensor model used with the `insEKF`

object. The sensor measures the velocity state, including a bias affected by random noise.

Customize the sensor model by inheriting from the `positioning.INSSensorModel`

interface class and implementing its methods. Note that only the `measurement`

method is required for implementation in the `positioning.INSSensorModel`

interface class. These sections provide an overview of how the `BiasSensor`

class implements the `positioning.INSSensorModel`

methods, but for details on their implementation, see the details of the implementation are in the attached `BiasSensor.m`

file.

**Implement sensorStates method**

To model bias, the `sensorStates`

method needs to return a state, `Bias`

, as a structure. When you add a `BiasSensor`

object to an `insEKF`

filter object, the filter adds the bias component to the state vector of the filter.

**Implement measurement method**

The measurement is the velocity component of the filter state, including the bias. Therefore, return the summation of the velocity component from the filter and the bias.

**Implement measurementJacobian method**

The `measurementJacobian`

method returns the partial derivative of the `measurement`

method with respect to the state vector of the filter as a structure. All the partial derivatives are `0`

, except the partial derivatives of the measurement with respect to the velocity and bias state components.

**Implement stateTransition method**

The `stateTransiton`

method returns the derivative of the sensor state defined in the `sensorStates`

method. Assume the derivative of the bias is affected by a white noise with a standard deviation of `0.01`

. Return the derivative as a structure. Note that this only showcases how to set up the method, and does not correspond to any practical application.

**Implement stateTransitionJacobian method**

Since the `stateTransiton`

function does not depend on the state of the filter, the Jacobian matrix is 0.

**Create and add inherited object**

Create a `BiasSensor`

object.

biSensor = BiasSensor

biSensor = BiasSensor with no properties.

Create an `insEKF`

object with the `biSensor`

object.

filter = insEKF(biSensor,insMotionPose)

filter = insEKF with properties: State: [17x1 double] StateCovariance: [17x17 double] AdditiveProcessNoise: [17x17 double] MotionModel: [1x1 insMotionPose] Sensors: {[1x1 BiasSensor]} SensorNames: {'BiasSensor'} ReferenceFrame: 'NED'

The filter state contains the bias component.

stateinfo(filter)

`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]
BiasSensor_Bias: 17

**Show customized BiasSensor class**

`type BiasSensor.m`

classdef BiasSensor < positioning.INSSensorModel %BIASSENSOR Sensor measuring velocity with bias % Copyright 2021 The MathWorks, Inc. methods function s = sensorstates(~,~) % Assume the sensor has a bias. Define a Bias state to enable % the filter to estimate the bias. s = struct('Bias',0); end function z = measurement(sensor,filter) % Measurement is the summation of the velocity measurement and % the bias. velocity = stateparts(filter,'Velocity'); bias = stateparts(filter,sensor,'Bias'); z = velocity + bias; end function dzdx = measurementJacobian(sensor,filter) % Compute the Jacobian, which is the partial derivative of the % measurement (velocity plus bias) with respect to the filter % state vector. % Obtain the dimension of the filter state. N = numel(filter.State); % The partial derviative of the Bias with respect to all the % states is zero, except the Bias state itself. dzdx = zeros(1,N); % Obtain the index for the Bias state component in the filter. bidx = stateinfo(filter,sensor,'Bias'); dzdx(:,bidx) = 1; % The partial derivative of the Velocity with respect to all the % states is zero, except the Velocity state itself. vidx = stateinfo(filter,'Velocity'); dzdx(:,vidx) = 1; end function dBias = stateTransition(~,~,dt,~) % Assume the derivative of the bias is affected by a zero-mean % white noise with a standard deviation of 0.01. noise = 0.01*randn*dt; dBias = struct('Bias',noise); end function dBiasdx = stateTransitonJacobian(~,filter,~,~) % Since the stateTransiton function does not depend on the % state of the filter, the Jacobian is all zero. N = numel(filter.State); dBiasdx = zeros(1,N); end end end

## Input Arguments

`sensor`

— Sensor model used with INS filter

object inherited from `positioning.INSSensorModel`

class

Sensor model used with an INS filter, specified as an object inherited from the `positioning.INSSensorModel`

abstract class.

`filter`

— INS filter

`insEKF`

object

INS filter, specified as an `insEKF`

object.

## Output Arguments

`z`

— Measurement

*M*-by-1 real-valued vector

Measurement, returned as an *M*-by-1 real-valued vector.

## Version History

**Introduced in R2022a**

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