# cameas

## Syntax

## Description

returns the expected measurement for a state based on the constant-acceleration
motion model. You can also use it as a measurement function in a Kalman filter. The
`measurement`

= cameas(`state`

)`state`

argument specifies the current state.

also specifies the measurement coordinate system, `measurement`

= cameas(`state`

,`frame`

)`frame`

.

also specifies the sensor position, `measurement`

= cameas(`state`

,`frame`

,`sensorpos`

)`sensorpos`

.

also
specifies the sensor velocity, `measurement`

= cameas(`state`

,`frame`

,`sensorpos`

,`sensorvel`

)`sensorvel`

.

specifies the measurement parameters,
`measurement`

= cameas(`state`

,`measurementParameters`

)`measurementParameters`

.

`[`

returns the measurement bounds used by a tracking filter (`measurement`

,`bounds`

] = cameas(___)`trackingEKF`

or `trackingUKF`

) in residual calculations. See the
`HasMeasurementWrapping`

property of the filter object for
more details.

## Examples

### Create Measurement from Accelerating Object in Rectangular Frame

Define the state of an object in 2-D constant-acceleration motion. The state is the position, velocity, and acceleration in both dimensions. The measurements are in rectangular coordinates.

state = [1,10,3,2,20,0.5].'; measurement = cameas(state)

`measurement = `*3×1*
1
2
0

The measurement is returned in three-dimensions with the *z*-component set to zero.

### Create Measurement from Accelerating Object in Spherical Frame

Define the state of an object in 2-D constant-acceleration motion. The state is the position, velocity, and acceleration in both dimensions. The measurements are in spherical coordinates.

```
state = [1,10,3,2,20,5].';
measurement = cameas(state,'spherical')
```

`measurement = `*4×1*
63.4349
0
2.2361
22.3607

The elevation of the measurement is zero and the range rate is positive. These results indicate that the object is moving away from the sensor.

### Create Measurement from Accelerating Object in Translated Spherical Frame

Define the state of an object moving in 2-D constant-acceleration motion. The state consists of position, velocity, and acceleration in each dimension. The measurements are in spherical coordinates with respect to a frame located at *(20;40;0)* meters from the origin.

```
state = [1,10,3,2,20,5].';
measurement = cameas(state,'spherical',[20;40;0])
```

`measurement = `*4×1*
-116.5651
0
42.4853
-22.3607

The elevation of the measurement is zero and the range rate is negative indicating that the object is moving toward the sensor.

### Create Measurement from Constant-Accelerating Object Using Measurement Parameters

Define the state of an object moving in 2-D constant-acceleration motion. The state consists of position, velocity, and acceleration in each dimension. The measurements are in spherical coordinates with respect to a frame located at *(20;40;0)* meters from the origin.

state2d = [1,10,3,2,20,5].';

The elevation of the measurement is zero and the range rate is negative indicating that the object is moving toward the sensor.

frame = 'spherical'; sensorpos = [20;40;0]; sensorvel = [0;5;0]; laxes = eye(3); measurement = cameas(state2d,'spherical',sensorpos,sensorvel,laxes)

`measurement = `*4×1*
-116.5651
0
42.4853
-17.8885

The elevation of the measurement is zero and the range rate is negative. These results indicate that the object is moving toward the sensor.

Put the measurement parameters in a structure and use the alternative syntax.

measparm = struct('Frame',frame,'OriginPosition',sensorpos,'OriginVelocity',sensorvel, ... 'Orientation',laxes); measurement = cameas(state2d,measparm)

`measurement = `*4×1*
-116.5651
0
42.4853
-17.8885

### Display Residual Wrapping Bounds for `cameas`

Specify a 2-D state and specify a measurement structure such that the function outputs azimuth, range, and range-rate measurements.

state = [10 1 0.1 10 1 0.1]'; % [x vx ax y vy ay]' mp = struct("Frame","Spherical", ... "HasAzimuth",true, ... "HasElevation",false, ... "HasRange",true, ... "HasVelocity",false);

Output the measurement and wrapping bounds using the `cameas`

function.

[measure,bounds] = cameas(state,mp)

`measure = `*2×1*
45.0000
14.1421

`bounds = `*2×2*
-180 180
-Inf Inf

## Input Arguments

`state`

— Current state

real-valued *3D*-by*N* matrix

Current state for constant-acceleration motion, specified as a real-valued
*3D*-by*N* matrix.
*D* is the number of spatial degrees of freedom of
motion and *N* is the number states. For each spatial
degree of motion, the state vector, as a column of the
`state`

matrix, takes the form shown in this
table.

Spatial Dimensions | State Vector Structure |
---|---|

1-D | `[x;vx;ax]` |

2-D | `[x;vx;ax;y;vy;ay]` |

3-D | `[x;vx;ax;y;vy;ay;z;vz;az]` |

For example, `x`

represents the
*x*-coordinate, `vx`

represents the
velocity in the *x*-direction, and `ax`

represents the acceleration in the *x*-direction. If the
motion model is in one-dimensional space, the *y*- and
*z*-axes are assumed to be zero. If the motion model is
in two-dimensional space, values along the *z*-axis are
assumed to be zero. Position coordinates are in meters. Velocity coordinates
are in meters/second. Acceleration coordinates are in
meters/second^{2}.

**Example: **`[5;0.1;0.01;0;-0.2;-0.01;-3;0.05;0]`

**Data Types: **`double`

`frame`

— Frame to report measurements

`'rectangular'`

(default) | `'spherical'`

Frame to report measurements, specified as `'rectangular'`

or
`'spherical'`

. When you specify frame as
`'rectangular'`

, a measurement consists of *x*,
*y*, and *z* Cartesian coordinates. When you
specify frame as `'spherical'`

, a measurement consists of azimuth,
elevation, range, and range rate.

**Data Types: **`char`

| `string`

`sensorpos`

— Sensor position

`[0;0;0]`

(default) | real-valued 3-by-1 column vector

Sensor position with respect to the navigation frame, specified as a real-valued 3-by-1 column vector. Units are in meters.

**Data Types: **`single`

| `double`

`sensorvel`

— Sensor velocity

`[0;0;0]`

(default) | real-valued 3-by-1 column vector

Sensor velocity with respect to the navigation frame, specified as a real-valued 3-by-1 column vector. Units are in m/s.

**Data Types: **`single`

| `double`

`laxes`

— Local sensor axes coordinates

`[1,0,0;0,1,0;0,0,1]`

(default) | 3-by-3 orthogonal matrix

Local sensor axes coordinates, specified as a 3-by-3 orthogonal matrix. Each column
specifies the direction of the local *x*-, *y*-, and
*z*-axes, respectively, with respect to the navigation frame. The
matrix is the rotation matrix from the global frame to the sensor frame.

**Data Types: **`single`

| `double`

`measurementParameters`

— Measurement parameters

structure | array of structures

Measurement parameters, specified as a structure or an array of structures. This table lists the fields in the structure.

Field | Description | Example |
---|---|---|

`Frame` | Frame used to report measurements, specified as one of these values: `'Rectangular'` — Detections are reported in rectangular coordinates.`'Spherical'` — Detections are reported in spherical coordinates.
In Simulink, when you create an object detection Bus, specify
| `'spherical'` |

`OriginPosition` | Position offset of the origin of the frame relative to the parent frame, specified as an `[x y z]` real-valued vector. | `[0 0 0]` |

`OriginVelocity` | Velocity offset of the origin of the frame relative to the parent frame, specified as a `[vx vy vz]` real-valued vector. | `[0 0 0]` |

`Orientation` | Frame rotation matrix, specified as a 3-by-3 real-valued orthonormal matrix. | `[1 0 0; 0 1 0; 0 0 1]` |

`HasAzimuth` | Logical scalar indicating if azimuth is included in the measurement. This
field is not relevant when the | `1` |

`HasElevation` | Logical scalar indicating if elevation information is included in the measurement. For
measurements reported in a rectangular frame, and if
`HasElevation` is false, the reported measurements assume 0
degrees of elevation. | `1` |

`HasRange` | Logical scalar indicating if range is included in the measurement. This
field is not relevant when the | `1` |

`HasVelocity` | Logical scalar indicating if the reported detections include velocity measurements. For a
measurement reported in the rectangular frame, if `HasVelocity`
is `false` , the measurements are reported as ```
[x y
z]
``` . If `HasVelocity` is `true` ,
the measurement is reported as `[x y z vx vy vz]` . For a
measurement reported in the spherical frame, if `HasVelocity`
is `true` , the measurement contains range-rate
information. | `1` |

`IsParentToChild` | Logical scalar indicating if `Orientation` performs a frame rotation from the parent coordinate frame to the child coordinate frame. When `IsParentToChild` is `false` , then `Orientation` performs a frame rotation from the child coordinate frame to the parent coordinate frame. | `0` |

If you want to perform only one coordinate transformation, such as a transformation from the body frame to the sensor frame, you must specify a measurement parameter structure. If you want to perform multiple coordinate transformations, you must specify an array of measurement parameter structures. To learn how to perform multiple transformations, see the Convert Detections to objectDetection Format (Sensor Fusion and Tracking Toolbox) example.

**Data Types: **`struct`

## Output Arguments

`measurement`

— Measurement of state

real-valued *N*-element row vector | real-valued *M*-by-*N* matrix

Measurement vector, returned as an *N*-element real-valued row vector
or an *M*-by-*N* real-valued matrix.
*M*, the size of each measurement, can vary depending on the
syntax. For more information, see the following table. *N*, the number
of measurements, is the same as the number of states. The format of the measurement
vector depends on the syntax.

When you do not specify the

`measurementParameters`

argument and set the`frame`

argument to`'rectangular'`

, the function outputs measurement vectors in the format of`[x;y;z]`

.When you do not specify the

`measurementParameters`

argument and set the`frame`

argument to`'spherical'`

, the function outputs measurement vectors in the format of`[az;el;r;rr]`

.When you specify the

`measurementParameters`

argument and set the`frame`

field to`'rectangular'`

, the size of the measurement vector depends on the value of the`HasVelocity`

field in the`measurementParameters`

structure. The measurement vector includes the Cartesian position and velocity coordinates of the tracked object with respect to the ego vehicle coordinate system.**Rectangular Measurements**`HasVelocity`

=`'false'`

`[x;y;z]`

`HasVelocity`

=`'true'`

`[x;y;z;vx;vy;vz]`

Position units are in meters and velocity units are in m/s.

When you specify the

`measurementParameters`

argument and set the`frame`

field to`'spherical'`

, the size of the measurement vector depends on the value of the`HasVelocity`

,`HasRange`

, and`HasElevation`

fields in the`measurementParameters`

structure. The measurement vector includes the azimuth angle,*az*, elevation angle,*el*, range,*r*, and range rate,*rr*, of the object with respect to the local ego vehicle coordinate system. Positive values for range rate indicate that an object is moving away from the sensor.**Spherical Measurements**`HasRange`

=`'true'`

`HasRange`

=`'false'`

`HasElevation`

=`'false'`

`HasElevation`

=`'true'`

`HasElevation`

=`'false'`

`HasElevation`

=`'true'`

`HasVelocity`

=`'false'`

`[az;r]`

`[az;el;r]`

`[az]`

`[az;el]`

`HasVelocity`

=`'true'`

`[az;r;rr]`

`[az;el;r;rr]`

`[az]`

`[az;el]`

Angle units are in degrees, range units are in meters, and range rate units are in m/s.

**Data Types: **`double`

`bounds`

— Measurement residual wrapping bounds

real-valued two-element row vector | *M*-by-2 real-valued matrix

Measurement residual wrapping bounds, returned as a two-element real-valued row vector or an
*M*-by-2 real-valued matrix, where *M* is the size of each
measurement. Each row of the matrix corresponds to the lower and upper bounds, respectively,
of each measurement in the `measurement`

output.

The function returns different bound values based on the `frame`

input.

If you specify

`frame`

as`'Rectangular'`

, each row of the matrix is`[-Inf Inf]`

, indicating that the filter did not wrap the measurement residual.

If you specify

`frame`

as`'Spherical'`

, the function returns bounds for each measurement based on the following:When

`HasAzimuth`

=`true`

, the matrix includes a row of`[-180 180]`

, indicating that the filter wrapped the azimuth residual in the range of`[-180 180]`

in degrees.When

`HasElevation`

=`true`

, the matrix includes a row of`[-90 90]`

, indicating that the filter wrapped the elevation residual in the range of`[-90 90]`

in degrees.When

`HasRange`

=`true`

, the matrix includes a row of`[-Inf Inf]`

, indicating that the filter did not wrap the range residual.When

`HasVelocity`

=`true`

, the matrix includes a row of`[-Inf Inf]`

, indicating that the filter did not wrap the range rate residual.

If you set any of the fields to `false`

, the returned
`bounds`

do not contain the corresponding row. For example, if
`HasAzimuth`

= `true`

, `HasElevation`

=
`false`

, `HasRange`

= `true`

,
`HasVelocity`

= `true`

, then the function returns the
bounds as:

-180 180 -Inf Inf -Inf Inf

The filter wraps the measuring residuals based on this equation:

$${x}_{wrap}=mod(x-\frac{a-b}{2},b-a)+\frac{a-b}{2}$$

where *x* is the residual to wrap, *a* is
the lower bound, *b* is the upper bound, *mod* is the
remainder after division, and *x*_{wrap} is the wrapped
residual.

**Data Types: **`single`

| `double`

## More About

### Azimuth and Elevation Angle Definitions

The *azimuth angle* of a vector is the angle between the
*x*-axis and its orthogonal projection onto the
*xy*-plane. The angle is positive when going from the
*x*-axis toward the *y*-axis. Azimuth angles lie between
–180 and 180 degrees. The *elevation angle* is the angle between the
vector and its orthogonal projection onto the *xy*-plane. The angle is
positive when going toward the positive *z*-axis from the
*xy*-plane.

## Extended Capabilities

### C/C++ Code Generation

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

## Version History

**Introduced in R2021a**

## See Also

### Functions

`constacc`

(Sensor Fusion and Tracking Toolbox) |`constaccjac`

(Sensor Fusion and Tracking Toolbox) |`cameasjac`

(Sensor Fusion and Tracking Toolbox) |`cvmeas`

|`ctmeas`

(Sensor Fusion and Tracking Toolbox) |`ctrvmeas`

(Sensor Fusion and Tracking Toolbox) |`singermeas`

(Sensor Fusion and Tracking Toolbox) |`initcaekf`

(Sensor Fusion and Tracking Toolbox) |`initcaukf`

(Sensor Fusion and Tracking Toolbox)

### Objects

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