# cameas

Measurement function for constant-acceleration motion

## Syntax

## Description

returns the measurement, for the constant-acceleration Kalman filter motion model in
rectangular coordinates. The `measurement`

= cameas(`state`

)`state`

argument specifies the
current state of the filter.

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`

.

## 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

## Input Arguments

`state`

— Kalman filter state vector

real-valued *3N*-element vector

Kalman filter state vector for constant-acceleration motion,
specified as a real-valued *3N*-element vector. *N* is
the number of spatial degrees of freedom of motion. For each spatial
degree of motion, the state vector 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`

— Measurement output frame

`'rectangular'`

(default) | `'spherical'`

Measurement output frame, specified as `'rectangular'`

or
`'spherical'`

. When the frame is `'rectangular'`

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

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

**Data Types: **`char`

`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: **`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: **`double`

`laxes`

— Local sensor coordinate axes

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

(default) | 3-by-3 orthogonal matrix

Local sensor coordinate axes, 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. That
is, the matrix is the rotation matrix from the global frame to the sensor frame.

**Data Types: **`double`

`measurementParameters`

— Measurement parameters

structure | array of structure

Measurement parameters, specified as a structure or an array of structures. The fields of the structure are:

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.
| `'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. | `1` |

`HasElevation` | Logical scalar indicating if elevation 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. | `1` |

`HasVelocity` | Logical scalar indicating if the reported detections include velocity measurements. For measurements reported in the rectangular frame, if `HasVelocity` is false, the measurements are reported as `[x y z]` . If `HasVelocity` is `true` , measurements are reported as `[x y z vx vy vz]` . | `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 only want to perform one coordinate transformation, such as a transformation from the body frame to the sensor frame, you only need to specify a measurement parameter structure. If you want to perform multiple coordinate transformations, you need to specify an array of measurement parameter structures. To learn how to perform multiple transformations, see the Convert Detections to objectDetection Format example.

**Data Types: **`struct`

## Output Arguments

`measurement`

— Measurement vector

*N*-by-1 column vector

Measurement vector, returned as an *N*-by-1 column vector. The form
of the measurement depends upon which syntax you use.

When the syntax does not use the

`measurementParameters`

argument, the measurement vector is`[x,y,z]`

when the`frame`

input argument is set to`'rectangular'`

and`[az;el;r;rr]`

when the`frame`

is set to`'spherical'`

.When the syntax uses the

`measurementParameters`

argument, the size of the measurement vector depends on the values of the`frame`

,`HasVelocity`

, and`HasElevation`

fields in the`measurementParameters`

structure.frame measurement `'spherical'`

Specifies 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****HasElevation**false true **HasVelocity**false `[az;r]`

`[az;el;r]`

true `[az;r;rr]`

`[az;el;r;rr]`

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

`'rectangular`

Specifies the Cartesian position and velocity coordinates of the tracked object with respect to the ego vehicle coordinate system.

**Rectangular measurements****HasVelocity**false `[x;y;y]`

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

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

**Data Types: **`double`

## More About

### Azimuth and Elevation Angle Definitions

Define the azimuth and elevation angles used in the toolbox.

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 in 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™.

## See Also

### Functions

`constacc`

|`constaccjac`

|`cameasjac`

|`constturn`

|`constturnjac`

|`ctmeas`

|`ctmeasjac`

|`constvel`

|`constveljac`

|`cvmeas`

|`cvmeasjac`

### Objects

**Introduced in R2018b**

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