Object Detections

Sensor detections are returned as a cell array of objectDetection objects. A detection contains these properties.

PropertyDefinition
TimeMeasurement time
MeasurementObject measurements
MeasurementNoiseMeasurement noise covariance matrix
SensorIndexUnique ID of the sensor
ObjectClassIDObject classification
MeasurementParametersParameters used by initialization functions of nonlinear Kalman tracking filters
ObjectAttributesAdditional information passed to tracker

Measurements and Measurement Noise

The sensor measures the coordinates of the target. The Measurement and MeasurementNoise values are reported in the coordinate system specified by the DetectionCoordinates property of the sensor.

When the DetectionCoordinates property is 'Scenario', 'Body', or 'Sensor rectangular', the Measurement and MeasurementNoise values are reported in rectangular coordinates. Velocities are only reported when the range rate property, HasRangeRate, is true.

When the DetectionCoordinates property is 'Sensor spherical', the Measurement and MeasurementNoise values are reported in a spherical coordinate system derived from the sensor rectangular coordinate system. Elevation and range rate are only reported when HasElevation and HasRangeRate are true.

Measurements are ordered as [azimuth, elevation, range, range rate]. Reporting of elevation and range rate depends on the corresponding HasElevation and HasRangeRate property values. Angles are in degrees, range is in meters, and range rate is in meters per second.

Measurement Coordinates

DetectionCoordinatesMeasurement and Measurement Noise Coordinates
'Scenario'

Coordinate Dependence on HasRangeRate

HasRangeRateCoordinates
true[x; y; z; vx; vy; vz]
false[x; y; z]
'Body'
'Sensor rectangular'
'Sensor spherical'

Coordinate Dependence on HasRangeRate and HasElevation

HasRangeRateHasElevationCoordinates
truetrue[az; el; rng; rr]
truefalse[az; rng; rr]
falsetrue[az; el; rng]
falsefalse[az; rng]

Measurement Parameters

The MeasurementParameters property consists of an array of structures that describe a sequence of coordinate transformations from a child frame to a parent frame or the inverse transformations (see Frame Rotation). In most cases, the longest required sequence of transformations is Sensor → Platform → Scenario.

If the detections are reported in sensor spherical coordinates and HasINS is set to false, then the sequence consists only of one transformation from sensor to platform. In the transformation, the OriginPosition is same as the MountingLocation property of the sensor. The Orientation consists of two consecutive rotations. The first rotation, corresponding to the MountingAngles property of the sensor, accounts for the rotation from the platform frame (P) to the sensor mounting frame (M). The second rotation, corresponding to the azimuth and elevation angles of the sensor, accounts for the rotation from the sensor mounting frame (M) to the sensor scanning frame (S). In the S frame, the x direction is the boresight direction, and the y direction lies within the x-y plane of the sensor mounting frame (M).

If HasINS is true, the sequence of transformations consists of two transformations – first form the scenario frame to the platform frame then from platform frame to the sensor scanning frame. In the first transformation, the Orientation is the rotation from the scenario frame to the platform frame, and the OriginPosition is the position of the platform frame origin relative to the scenario frame.

Trivially, if the detections are reported in platform rectangular coordinates and HasINS is set to false, the transformation consists only of the identity.

The fields of MeasurementParameters are shown here. Not all fields have to be present in the structure. The set of fields and their default values can depend on the type of sensor.

FieldDescription
Frame

Enumerated type indicating the frame used to report measurements. When detections are reported using a rectangular coordinate system, Frame is set to 'rectangular'. When detections are reported in spherical coordinates, Frame is set 'spherical' for the first struct.

OriginPosition

Position offset of the origin of the child frame relative to the parent frame, represented as a 3-by-1 vector.

OriginVelocity

Velocity offset of the origin of the child frame relative to the parent frame, represented as a 3-by-1 vector.

Orientation

3-by-3 real-valued orthonormal frame rotation matrix. The direction of the rotation depends on the IsParentTochild field.

IsParentToChild

A logical scalar indicating if Orientation performs a frame rotation from the parent coordinate frame to the child coordinate frame. If false, Orientation performs a frame rotation from the child coordinate frame to the parent coordinate frame.

HasElevation

A logical scalar indicating if elevation is included in the measurement. For measurements reported in a rectangular frame, and if HasElevation is false, the measurements are reported assuming 0 degrees of elevation.

HasAzimuthA logical scalar indicating if azimuth is included in the measurement.
HasRangeA logical scalar indicating if range is included in the measurement.
HasVelocity

A 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].

Object Attributes

Object attributes contain additional information about a detection:

AttributeDescription
TargetIndex

Identifier of the platform, PlatformID, that generated the detection. For false alarms, this value is negative.

SNR

Detection signal-to-noise ratio in dB.