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Channel Definitions

Standard Channels

Speed

Speed is a Doppler derived channel coming directly from our GPS engine, this is the 2D speed and has no direction. This data is calculated directly at the reference antenna

 

If IMU integration is on, speed will be filtered using a Kalman filter producing a less noisy channel. This is also lever arm compensated to eliminate the effect of body movement on the roof mounted measurement location of the GPS antenna.

Also in the case that GPS signal is lost the IMU will continue to provide speed data however this will degrade in accuracy over time. It is recommended not to use data that has been without GPS for more than 10 seconds.

 

LongAcc

LongAcc is the longitudinal acceleration value that is derived by differentiating the longitudinal component of the Doppler derived Speed calculated at the reference antenna.

This measurement is independent of body pitch angle.

If IMU integration is on, LongAcc will be filtered using a Kalman filter producing a more noise free channel, that is also lever arm compensated to remove body pitch induced overshoot during high dynamic braking or acceleration. In the case that GPS signal is lost the IMU will continue to provide acceleration data however this will degrade in accuracy over time. It is recommended not to use data that has been without GPS for more than 10 seconds.

 

LatAcc

LatAcc is the lateral acceleration value that is derived by differentiating the Doppler derived Speed and Heading channels calculated at the reference antenna.

This measurement is independent of body roll angle.

 

If IMU integration is on, LatAcc will be filtered using a Kalman filter producing a more noise free channel, that is also lever arm compensated to remove body pitch induced overshoot during high dynamic braking or acceleration. In the case that GPS signal is lost the IMU will continue to provide acceleration data however this will degrade in accuracy over time. It is recommended not to use data that has been without GPS for more than 10 seconds.

 

Heading

Heading is a Doppler derived channel coming directly from the GPS engine. This heading will be the ‘course over ground’ bearing at the antenna location with respect to North, irrespective of vehicle direction.  

 

If IMU integration is on, the Heading value will be filtered using a Kalman filter producing a more noise free channel that is also lever arm compensated to remove body pitch and roll induced overshoot during high dynamic manoeuvres.  In the case that GPS signal is lost the IMU will continue to provide heading data however this will degrade in accuracy over time. It is recommended not to use data that has been without GPS for more than 10 seconds.

 

Height

Height is a positional calculated channel using trilateration from four or more observed satellites. As such it is prone to drift as satellite signal paths are bent through the Earth’s upper Ionosphere . This culminates in a typical accuracy in an open area with respect to absolute position of +/- 3m.

Instantaneous jumps in this channel can occur when a satellite signal is lost or gained.

 

If IMU integration is on, the Height value will be filtered using a Kalman filter producing a less noisy channel. IMU integration will oppose the instantaneous jump in position caused by a satellite signal loss or gain.

Lever arm compensation is also applied to remove the overshoot of position caused by the effect body movement.

In the case that GPS signal is lost the IMU will continue to provide height data however this will degrade in accuracy over time. It is recommended not to use data that has been without GPS for more than 10 seconds.

 

Relative Height

This an integration of Vertical Velocity performed by the VBOX Tools software when a logged file is loaded. It will be zero at the beginning of the file.

This channel has a very high height accuracy over short periods of time and is resilient to satellites appearing or disappearing .

 

Vertical Velocity

Vertical speed is a Doppler derived channel; it has a direction associated (+ve when climbing, -ve when descending).

 

If IMU integration is on, the Vertical speed value will be filtered using a Kalman filter producing a less noisy channel. In the case that GPS signal is lost the IMU will continue to provide vertical speed data however this will degrade in accuracy over time. It is recommended not to use data that has been without GPS for more than 10 seconds.

 

Satellites

Lists the total number of satellites the unit is currently tracking by adding the channels GPS satellites and GLONASS satellites. This excludes SBAS satellites and cannot exceed 31.

 

Glonass Satellites

Lists the total number of GLONASS satellites the unit is currently tracking in the solution. This Excludes SBAS satellites.

 

GPS Satellites

Lists the total number of GPS satellites the unit is currently tracking in the solution. This Excludes SBAS satellites.

 

Brake trigger

The brake trigger is an oversampled digital input that is used for identifying exactly when the brake pedal is pressed for brake testing or event marking.

 

Latitude

Latitude is a geographic coordinate that specifies the north-south position of a point on the Earth's surface. Latitude is an angle produced in the GPS engine using trilateration of satellite time signals from four or more observable satellites. Latitude ranges from 0° at the Equator to 90° (North or South) at the poles.

 

This will be augmented and ‘lever arm compensated’ using inertial data if an IMU is present and IMU integration switched on.

 

Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angle produced in the GPS engine using trilateration of satellite time signals from four or more observable satellites. Longitude ranges from 0° at the prime meridian to 180° east and west.

 

This will be augmented and ‘lever arm compensated’ using inertial data if an IMU is present and IMU integration switched on.

 

DGPS

This channel indicates if the GPS is currently using a DGPS correction data to mitigate for GPS positional propagation errors. An improvement in the positional accuracy of the VBOX depends on what type of DGPS message is being used.

 

UTC Time

UTC is the universal coordinated time, which is accurate to about a nanosecond (billionth of a second) per day.

 

Distance

This channel is the accumulative total of distance in metres since the start of the file. This channel is calculated via integration of speed, so is a derivative of a Doppler derived channel

 

Time

This channel is the accumulative total of time in seconds since the start of the file

 

Radius of Turn

The radius of turn channel is derived from the speed and lateral acceleration channels. As IMU integration has an effect on both of these channels, the radius of turn data will also be smoother when IMU integration is enabled.

 

Speed Quality

This is an RMS indication of the quality/accuracy of the current measured GPS speed. It is expressed in km/h. 

 

Centre Line Deviation

This is a measurement vehicle lateral movement (m). This parameter uses a previously sampled test lane heading as a reference and then from the start of each test creates a lateral deviation measurement. So if the vehicle pulls left during a brake stop then this parameter will display a +ve value in metres.

 

Solution Type

A numerical representation of the mode of DGPS correction currently being employed by the GPS receiver :-

1= Stand alone

3= RTK Float

4 = RTK Fixed

IMU Channels

The following Channels are only present if a Racelogic IMU (e.g. IMU04) is connected to a VBOX

 

YawRate

Degrees /second measurement from a gyro in the YAW plane of a vehicle. +ve clockwise

 

X_Accel

Accelerometer measurement in the vehicle longitudinal plane, +ve for acceleration. This measurement is not compensated for gravitational influence.

Y_Accel

Accelerometer measurement in the vehicle lateral plane, +ve for counter clockwise rotation. This measurement is not compensated for gravitational influence.

 

Temp

Value of temperature from the IMU internal temperature sensor, NOT ambient temperature measurement.

 

PitchRate

Rotational rate measurement from a gyro in the longitudinal axis of a vehicle. -ve nose down.

 

RollRate

Rotational rate measurement from a gyro in the lateral axis of a vehicle. +ve for counter clockwise rotation.

 

Z_Accel

Accelerometer measurement in the vehicle vertical,  +ve for upward acceleration. This measurement is not compensated for gravitational influence.

 

Dual Antenna Channels

The following channels are only present if the ‘Dual Antenna’ mode is enabled on a VBOX

True Heading

This is a measurement of heading from the reference antenna to the secondary antenna with respect to north. When mounted on a vehicle it becomes the measurement of heading that the vehicle is facing.

 

Slip_Angle

Slip angle is the difference between Heading & True Heading channels. This is then a measurement of body slip angle at the reference antenna.

As IMU integration has an effect on the heading value, IMU integration will result in a less noisy Slip_Angle channel, it will also translate the measurement from the antenna location to the IMU location.

 

Pitch_Angle

Pitch Angle is the angle between the two GPS antennas when configured in “Pitch mode”. This channel gives an accurate measurement of absolute vehicle pitch relative to a zero line. As it is a direct angular measurement, it does not suffer drift over time.

 

Lat_Vel

Lateral Velocity is speed of the vehicle with respect to lateral direction of the vehicle body (90o to the direction of travel):

It is derived from GPS speed and Slip angle; GPS speed is the speed of the vehicle in the direction of travel of the GPS antenna.

 

The VB3iSL's Lat_Vel (Lateral velocity) CAN channel is calculated in the following way...

Lateral Velocity = Speed x SIN (Slip angle)

 

 

Lat and Long Velocity relationship to slip angle:

Slip angle Arctan(Lateral velocity/Longitudinal velocity) 

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Lng_Vel

Longitudinal Velocity is speed of the vehicle with respect to longitudinal direction of the vehicle body:

It is derived from GPS speed and Slip angle; GPS speed is the speed of the vehicle in the direction of travel of the GPS antenna.

 

The VB3iSL's Long_Vel (Lateral velocity) CAN channel is calculated in the following way...

Longitudinal Velocity = Speed x COS (Slip angle)

 

 

Lat and Long Velocity relationship to slip angle:

Slip angle = Arctan(Lateral velocity/Longitudinal velocity) 

Yaw_Rate

This Yaw rate measurement is derived from the rate of change of True Heading. As such it is noisier than the direct gyro measurement of Yaw rate from the Inertial Measurement Unit.

 

Roll_Angle

Roll Angle is the angle between the two GPS antennas when configured in “Roll mode”. This channel gives an accurate measurement of absolute vehicle roll relative to a zero line. As it is a direct angular measurement it does suffer drift over time.

 

Slip_COG, Slip_FL, Slip_FR, Slip_RL, Slip_RR

These channels are body slip angle measurements translated to different locations on the vehicle, using yaw rate and x and y offsets in metres.

 

True_Head2

This is a measurement of heading from the reference antenna to the secondary antenna with respect to north. When mounted on a vehicle it becomes the measurement of heading that the vehicle is facing. When an IMU is connected to the VBOX then this True Heading is combined with Yaw rate in an online filter to further reduce the amount of noise. This is used in the ADAS vehicle separation calculations.

Note: it is never used in Slip Angle.

 

Kalman Filter Channels

The following channels are only available if an IMU04 is connected to a VBOX v3 with IMU integration switched on.

 

Latitude_raw

This contains the raw GPS Latitude value derived from positional data.

 

Longitude_raw

This contains the raw GPS Longitude value derived from positional data.

 

Height_raw

This contains the raw GPS height value derived from positional data.

 

Speed_raw

This contains the raw GPS data from the Doppler derived GPS Speed.

 

Vertical_Velocity_raw

This contains the raw GPS data from the Doppler derived vertical Speed.

 

Heading_raw

This channel contains the raw GPS data from the Doppler derived GPS Heading.

 

IMU Kalman

This channel indicates the Kalman Filter status in numerical form.

 

RMS_HPOS

Accuracy of the current GPS horizontal positional measurement.

 

RMS_VPOS

Accuracy of the current GPS vertical positional measurement.

 

RMS_HVEL

Accuracy of the current GPS horizontal velocity measurement

 

RMS_VVEL

Accuracy of the current GPS vertical velocity measurement.

 

Head_imu

Head_imu is the heading of the body of the vehicle generated by the Kalman filter using GPS and Inertial data. This is the IMU integration equivalent of twin antenna ‘True Heading’.

 

Pitch_imu

Pitch_imu is the pitch angle measured in degrees, generated from the Kalman filter using GPS and inertial data.

 

Roll_imu

Roll_imu is the roll angle measured in degrees, generated from the Kalman filter using GPS and inertial data.

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Last modified
11:43, 28 Jun 2017

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