Reference Manual¶

1. Introduction¶

INS1000 is an integrated navigation system consisting of an inertial measurement unit (IMU) and other sensors. Thus it can output continuously the position, velocity and attitude information of the vehicle. A dual-antenna GNSS receiver is used as the primary aiding sensor. Also supported is a distance measurement indicator (DMI) which can be attached to a wheel of the vehicle/robot to measure the rotation rate of the wheel. Integration of a DMI would give an improved solution in challenging environments: urban canyons, tunnels or indoor. This document explains how to use the system.

2. The IMU Frame and the Body Frame¶

The IMU frame is the frame in which the IMU’s measurement output is generated. The direction of the axes of an IMU can be identified using the accelerometer signal. When an accelerometer is placed in upward direction on a level surface, its output should be approximately 9.8 \(m/s^{2}\).On the other hand, if it is place in downward direction, the output should be -9.8 \(m/s^{2}\). The positive direction of all three axes of an IMU can be identified this way.

The body frame is the frame in which the inertial navigation solution is generated. The center of the IMU frame coincides with that of the body frame. However, there can be differences in the attitude between the two frames due to physical limitations in the installation of the IMU. For a vehicle, the forward-right-down is typically the body frame of choice. Thus, there will be a rotation matrix \(C_{IMU}^{b}\) to transform the IMU measurements to the body frame and, for the example below, it is written as

\[\begin{split}C_{IMU}^{b} = \begin{bmatrix} c_{11}& c_{12} & c_{13} \\ c_{21}& c_{22} & c_{23}\\ c_{31}& c_{32} & c_{33} \end{bmatrix}=\begin{bmatrix} 1 & 0 & 0\\ 0 & -1 & 0 \\ 0 & 0 & -1 \end{bmatrix}\end{split}\]

_images/The_IMU_frame_and_the_body_frame.png

Figure 1: The IMU frame and the body frame

IMU X	IMU Y	IMU Z	Transformation Matrix
Forward	Right	Down	[1,0,0; 0,1,0; 0,0,1]
Forward	Left	Up	[1,0,0; 0,-1,0; 0,0,-1]
Forward	Down	Left	[1,0,0; 0,0,-1; 0,1,0]
Forward	Up	Right	[1,0,0; 0,0,1; 0,-1,0]
Backward	Left	Down	[-1,0,0; 0,-1,0; 0,0,1]
Backward	Right	Up	[-1,0,0; 0,1,0; 0,0,-1]
Backward	Up	Left	[-1,0,0; 0,0,-1; 0,-1,0]
Backward	Down	Right	[-1,0,0; 0,0,1; 0,1,0]
Right	Backward	Down	[0,-1,0; 1,0,0; 0,0,1]
Right	Forward	Up	[0,1,0; 1,0,0; 0,0,-1]
Right	Up	Backward	[0,0,-1; 1,0,0; 0,-1,0]
Right	Down	Forward	[0,0,1; 1,0,0; 0,1,0]
Left	Forward	Down	[0,1,0; -1,0,0; 0,0,1]
Left	Backward	Up	[0,-1,0; -1,0,0; 0,0,-1]
Left	Up	Forward	[0,0,1; -1,0,0; 0,-1,0]
Left	Down	Backward	[0,0,-1; -1,0,0; 0,1,0]
Up	Forward	Left	[0,1,0; 0,0,-1; -1,0,0]
Up	Backward	Right	[0,-1,0; 0,0,1; -1,0,0]
Up	Right	Forward	[0,0,1; 0,1,0; -1,0,0]
Up	Left	Backward	[0,0,-1; 0,-1,0; -1,0,0]
Down	Forward	Right	[0,1,0; 0,0,1; 1,0,0]
Down	Backward	Left	[0,-1,0; 0,0,-1; 1,0,0]
Down	Left	Forward	[0,0,1; 0,-1,0; 1,0,0]
Down	Right	Backward	[0,0,-1; 0,1,0; 1,0,0]

Table 1: List of IMU to body frame transformation matrices

3. Measuring Lever Arm¶

The lever-arm is the relative position of other sensors from the center of the IMU. To make the measurement process easier, we make a cross-mark on top of the IMU housing and publishes the vector from the center of the IMU to the mark, \(l_{I}^{IMU}\), which is called the internal lever-arm. Thus users can measure the relative position from the cross-mark to other sensors which is referred to as the external lever-arm in the body frame, \(l_{E}^{b}\). Therefore, the total lever-arm vector is computed as follows:

\[C_{IMU}^{b}l_{I}^{IMU}+l_{E}^{b}\]

The following methods can be used to precisely measure the lever-arms:

Computer Aided Design (CAD) Software
Close-range Photogrammetry
Precision Surveying using total stations or theodolites together with GNSS

4. NTRIP Client¶

A base station can send out RTCM messages to support the RTK, which enables cm-level positioning accuracy. Networked Transport of RTCM via Internet Protocol (NTRIP) is a protocol to stream the RTCM data over the internet. The user can configure the NTRIP client settings using the control software.

5. User ICD Messages¶

As shown in Figure 2, all ICD messages are composed of header, payload and checksum parts. The header’s size is 6 bytes containing 2 sync bytes, message ID, message sub-ID and payload length.

Header (6 bytes)

Payload

CheckSum (2 bytes)

Figure 2: Message structure

The checksum shall be computed over the payload part using the Fletcher-16 algorithm as below sample code. Note that all multi-byte entries are written in little-endian format.

checksum_A = checksum_B = 0;
for (i = 0; i < payload_length; ++i)
{
    checksum_A += payload[i];
    checksum_B += checksum_A;
}

5.1. Kalman Filter Navigation Message (1 Hz)¶

This message is an output of the navigation message at the center of the IMU in 1 Hz synchronized with the GNSS measurements. If the inertial navigator is not running, however, this message contains GNSS-only solutions of the primary GNSS antenna.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x01
5	uint16_t	Payload length	91
6	double	System time	seconds
7	double	GPS time; see Note 1	seconds
8	double	Latitude	radians
9	double	Longitude	radians
10	double	Ellipsoidal height	m
11	double	Velocity in north	m/s
12	double	Velocity in east	m/s
13	double	Velocity in down	m/s
14	double	Roll, rotation about the x-axis	radians
15	double	Pitch, rotation about the y-axis	radians
16	double	Heading, rotation about the z-axis	radians
17	uint8_t	Position mode	See Note 2
18	uint8_t	Velocity mode	See Note 2
19	uint8_t	Attitude status	0: Invalid, 1: Coarse, 2: Fine
20	uint8_t	Checksum A
21	uint8_t	Checksum B

Note

GPS seconds since starting week; thus this will not rollover after 604800.
Position and velocity mode are defined as follows:
- 0: Invalid,
- 1: Dead-reckoning (navigating with inertial measurements only),
- 2: Stand-alone (autonomous or single point positioning),
- 3: Precise point positioning (using precise ephemeris data)
- 4: Code differential (using code-corrections from base stations or SBAS)
- 5: RTK float
- 6: RTK fixed
- 7: User aiding (aiding by the user input)

5.2. Satellite Signal Strength¶

This message delivers the satellite signal strength information obtained from the GNSS observable.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x02
5	uint16_t	Payload length	19 + N_SV * 10
6	double	System time	seconds
7	double	GPS time
8	uint8_t	Receiver ID
9	uint8_t	Antenna ID
10	uint8_t	Number of satellites (N_SV)
11	uint8_t	SV system; see Note 1	First satellite data
12	uint8_t	SVID; see Note 2
13	float	L1 C/N0 (dB-Hz)
14	float	L2 C/N0 (dB-Hz)
15	uint8_t	SV system	Second satellite data
16	uint8_t	SVID
17	float	L1 C/N0 (dB-Hz)
18	float	L2 C/N0 (dB-Hz)
…
	uint8_t	Checksum A
	uint8_t	Checksum B

Note

0: GPS, 1: GLONASS, 2: Galileo, 3: QZSS, 4: Beidou, 5: SBAS
SVID is the unique satellite number used in each satellite system; for GPS it is the PRN number and for GLONASS it is the SLOT number.

5.3. SV Visibility¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x03
5	uint16_t	Payload length	18 + N_SV * 10
6	double	System time	seconds
7	double	GPS time	seconds
8	uint8_t	Receiver number
9	uint8_t	N_SV	Number of SV data
10	uint8_t	SV system	First satellite data
11	uint8_t	SVID
12	float	Azimuth (deg)
13	float	Elevation (deg)
14	uint8_t	SV system	Second satellite data
15	uint8_t	SVID
16	float	Azimuth (deg)
17	float	Elevation (deg)
…
	uint8_t	Checksum A
	uint8_t	Checksum B

5.4. Install Parameters¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x04
5	uint16_t	Payload length	72+N_ANT*32
6	double[3][3]	IMU axes transformation matrix
7	uint8_t	N_ANT	Number of antennas
8	double[3]	Lever-arm vector of 1st antenna	m
9	double	Lever-arm variance of 1st antenna	\(m^{2}\)
10	double[3]	Lever-arm vector of 2nd antenna	m
11	double	Lever-arm variance of 2nd antenna	\(m^{2}\)
…
	uint8_t	Checksum A
	uint8_t	Checksum B

5.5. Nav Uncertainty Message¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x05
5	uint16_t	Payload length	32
6	double	System time	seconds
7	double	Position RMS	m
8	double	Velocity RMS	m/s
9	double	Attitude RMS	deg
10	uint8_t	Checksum A
11	uint8_t	Checksum B

5.6. Product ID Message¶

This message contains the identification number of the product. To receive this message send the message defined in Section 8.1.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x06
5	uint16_t	Payload length	2
6	uint16_t	Product ID
7	uint8_t	Checksum A
8	uint8_t	Checksum B

5.7. Navigation Data Message (High Rate)¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x07
5	uint16_t	Payload length	99
6	double	System time	seconds
7	double	GPS time of week	seconds
8	double	Latitude	deg
9	double	Longitude	deg
10	double	Ellipsoidal height	m
11	double[3]	Velocity in NED	m/s
12	double[4]	Body to NED attitude quaternion	See Note 1 in Section 6.13
13	uint8_t	Alignment mode
14	uint16_t	GPS week number
15	uint8_t	Checksum A
16	uint8_t	Checksum B

5.8. Scaled Raw IMU Data¶

This message contains scaled raw IMU data. The reference frame of this data is the IMU frame.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x08
5	uint16_t	Payload length	56
6	double	System time	seconds
7	double[3]	Acceleration	\(m/s^{2}\)
8	double[3]	Rotation rate	degrees/s
9	uint8_t	Checksum A
10	uint8_t	Checksum B

5.9. Solution Status (1 Hz)¶

This message shows the Kalman filter solution status. The RMS of the position, velocity and attitude is the squre-root of the diagonal elements of the covariance matrix of the Kalman filter.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x09
5	uint16_t	Payload length	92
6	double	System time	seconds
7	uint8_t	Number of SVs used
8	uint8_t	Processing mode
9	uint16_t	GPS week number; if 0 time is not synced to GPS
10	double	GPS time of week	seconds
11	double[3]	Position RMS (NED)	m
12	double[3]	Velocity RMS (NED)	m/s
13	double[3]	Attitude RMS (NED)	deg
14	uint8_t	Checksum A
15	uint8_t	Checksum B

5.10. Repackaged GSV Message¶

This is a repackaged NMEA GSV message generated by the receiver.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x0A
5	uint16_t	Payload length	length 12 + N_SV * 5
6	double	System time	seconds
7	uint8_t	Receiver number
8	uint8_t	Antenna ID
9	uint8_t	SV system
10	uint8_t	N_SV
11	uint8_t	SVID	SVID of 1st SV
12	uint8_t	Elevation	deg
13	uint16_t	Azimuth	deg
14	uint8_t	SNR	db-Hz
15	uint8_t	SVID	SVID of 2nd SV
16	uint8_t	Elevation	deg
17	uint16_t	Azimuth	deg
18	uint8_t	SNR	db-Hz
…
	uint8_t	Checksum A
	uint8_t	Checksum B

5.11. Vehicle Dynamics Message¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x0B
5	uint16_t	Payload length	67
6	double	System time	seconds
7	double	GPS time of week	seconds
8	double[3]	Acceleration in body frame. See Note 2 in Section 5.13
9	double[3]	Rotation rate in body frame. See Note 3 in Section 5.13
10	uint16_t	GPS week number
11	uint8_t	Alignment mode
12	uint8_t	Checksum A
13	uint8_t	Checksum B

5.12. Distance Measurement Indicator Data12¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x0C
5	uint16_t	Payload length	13
6	double	System time	seconds
7	int32_t	Pulse count
8	uint8_t	DMI ID
9	uint8_t	Checksum A
10	uint8_t	Checksum B

5.13. Compact Navigation Message (High Rate)¶

This message is a high-rate real-time navigation output at the position defined by the user.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x0D
5	uint16_t	Payload length	119
6	double	System time if week = 0, otherwise GPS timeof week	seconds
7	double	Latitude	degrees
8	double	Longitude	degrees
9	float	Ellipsoidal height	m
10	float[3]	Velocity in North, East, Down	m/s
11	float[4]	Attitude quaternion; see Note 1	Scalar, X, Y, Z
12	float[3]	Acceleration in body frame; see Note 2	m/s2
13	float[3]	Rotation rate in body frame; see Note 3	degrees/s
14	float[3]	Position RMS in NED	m
15	float[3]	Velocity RMS in NED	m/s
16	float[3]	Attitude RMS in NED	degrees
17	uint16_t	GPS week number	If 0 time is not synced to GPS
18	uint8_t	Alignment status	0: Invalid, 1: Coarse, 2: Fine
19	uint8_t	Checksum A
20	uint8_t	Checksum B

Note

Attitude quaternion for the transformation from the body frame to the NED frame, \(q_{b}^{n}\). Note that the quaternion in ROS is defined as (X, Y, Z, scalar). The DCM corresponding to \(q_{b}^{n}\) can be computed as follows:

\[\begin{split}C_{b}^{n} = \begin{bmatrix} q_{0}^{2}+ q_{1}^{2}- q_{2}^{2}- q_{3}^{2} & 2(q_{1}q_{2}-q_{0}q_{3}) & 2(q_{1}q_{3}+q_{0}q_{2}) \\ 2(q_{1}q_{2}+q_{0}q_{3})& q_{0}^{2}- q_{1}^{2}+q_{2}^{2}- q_{3}^{2} & 2(q_{2}q_{3}-q_{0}q_{1})\\ 2(q_{1}q_{3}-q_{0}q_{2}) & 2(q_{2}q_{3}+q_{0}q_{1}) & q_{0}^{2}-q_{1}^{2}- q_{2}^{2}+ q_{3}^{2} \end{bmatrix}\end{split}\]

where \(q_{i}\) are elements of \(q_{b}^{n}\). Let \(C_{b}^{n} = \begin{Bmatrix}c_{ij}\end{Bmatrix}\) then if \(\begin{vmatrix}c_{31}\end{vmatrix}< 0.9999\) the Euler angles can be computed as follows:

\[\phi =atan2(c_{32},c_{33})\]

\[\Theta = atan\begin{pmatrix}-c_{31}/\sqrt{c_{32}^{2}+c_{33}^{2}}\end{pmatrix}\]

\[\psi = atan2(c_{21},c_{11})\]

where \(\phi\), \(\Theta\) and \(\psi\) are the roll, pitch and heading, respectively.

Acceleration output is corrected for the gravity, Coriolis force and the estimated accelerometer biases: \(f^{b}-b_{a}+C_{e}^{b}(g^{e}-2w_{ie}^{e}\times v^{e} )\) where \(f^{b}\) is the specific force measurement from the IMU, \(b_{a}\) estimated accelerometer bias, \(C_{e}^{b}\) the DCM for the transformation from the ECEF to the body frame, \(g^{e}\) the gravity vector computed from the model, \(w_{ie}^{e}\) the earth’s rotation rate vector, and \(v^{e}\) the velocity vector.
Rotation rate output is corrected for the earth rotation rate and the estimated gyro biases, i.e., \(w_{ie}^{e}\).

5.14. NMEA PECNM Message¶

This message is NMEA style text message corresponding to the message in Section 5.13.

5.15. NMEA GPRMC Message¶

This is the NMEA GPRMC message generated by the primary GNSS receiver.

5.16. Time Sync Message¶

This message contains the time sync message between the system time and GPS time. It gets generated at every PPS event. The GPS time corresponding to the system time can be obtained by

GPS time = System computer time - Bias

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x10
5	uint16_t	Payload length	16
6	double	System computer time	seconds
7	double	Bias with respect to GPS time	seconds
8	uint8_t	Checksum A
9	uint8_t	Checksum B

5.17. Raw GNSS Data Message¶

This message contains raw data generated by the GNSS receivers.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x11
5	uint16_t	Payload length	10+N
6	double	System computer time	seconds
7	uint8_t	Receiver number
8	uint8_t	Receiver type
9	uint8_t[N]	Raw GNSS data
10	uint8_t	Checksum A
11	uint8_t	Checksum B

5.18. Engine Version Message¶

This message shows the engine version of the system. To receive this message the user needs to send an 8-byte binary message “0xAF 0x02 0x06 0x0B 0x01 0x02 0x02 0x02” to the system.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x12
5	uint16_t	Payload length	N
6	char[N]	Engine version string
7	uint8_t	Checksum A
8	uint8_t	Checksum B

5.19. GNSS Receiver Acknowledge Message¶

This message shows the acknowledge response from a GNSS receiver.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x13
5	uint16_t	Payload length	2
6	uint8_t	Receiver number
7	uint8_t	Receiver type
8	uint8_t	Checksum A
9	uint8_t	Checksum B

5.20. GNSS Antenna Lever-Arm Calibration Data¶

Although it is recommended to accurately measure the lever-arms, sometimes it is very difficult to measure them. In this case the user can let the system calibrate the lever-arm vector. The calibration, however, must be done in an open-sky area with RTK enabled. For the primary antenna, the trajectory must include frequent turns, up-hill or down-hill driving for a considerably long time (one hour or more). Thus it would be the best to measure precisely with other instruments. Also the dual-antenna solution cannot be used in the solution during the calibration mode. So the INS initialization must be done with GNSS velocity.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x14
5	uint16_t	Payload length	57
6	double	Internal computer time	seconds
7	double[3]	Lever arm vector in body frame
8	double[3]	Variance	m2
9	uint8_t	Antenna indicator; see Note 1	0: pri, 1: sec-pri
10	uint8_t	Checksum A
11	uint8_t	Checksum B

Note

When antenna indicator is ‘1’ the message outputs the vector from the primary to the secondary antenna in the body frame. To get the lever-arm of the secondary antenna, the primary lever-arm vector must be added. Shown in Figure is a plot of this message for a lever-arm of the secondary antenna with respect to the primary antenna. It is recommended to take the mean values after the convergence.

_images/Example_of_a_lever-arm_calibration.png

Figure 4: The IMU frame and the body frame

5.21. DMI Lever-Arm Calibration Data¶

TBD.

5.22. Geoid Height¶

This message outputs the Geoid height, which is the height of Geoid above the ellipsoid. The height above Geoid, treated normally as the height above mean sea level (MSL), can be computed as follows:

Height above MSL = Height above ellipsoid - Geoid height

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x16
5	uint16_t	Payload length	12
6	double	GPS time	seconds
7	float	Geoid height	m
8	uint8_t	Checksum A
9	uint8_t	Checksum B

5.23. Corrected IMU Data¶

This message contains IMU data corrected for the sensor biases estimated by the fusion algorithm. Note that the effect of the gravity and the Earth’s rotation rate is still included in the sensor data. The reference frame of this data is the user body frame and thus the rotation from the IMU frame to the user body frame is applied.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x17
5	uint16_t	Payload length	58
6	double	GPS time of week	seconds
7	double[3]	Acceleration	m/s2
8	double[3]	Rotation rate	degrees/s
9	uint16_t	GPS week number
10	uint8_t	Checksum A
11	uint8_t	Checksum B

5.24. GPS-UTC Time Offset¶

This message contains the offset between the GPS time and the UTC. Note that GPS time is ahead of the UTC, which is called the leap seconds.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x05
4	uint8_t	Message sub-ID	0x18
5	uint16_t	Payload length	1
6	uint8_t	GPS - UTC time offset	seconds
7	uint8_t	Checksum A
8	uint8_t	Checksum B

5.25. NMEA GGA Message¶

This is the NMEA GGA message generated by the primary GNSS receiver.

6. System Diagnostic Messages¶

6.1. Text Message¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x07
4	uint8_t	Message sub-ID	0x00
5	uint16_t	Payload length	N
6	char[N]	Text
7	uint8_t	Checksum A
8	uint8_t	Checksum B

6.2. Sensor Message Count¶

This message indicates the activity of each sub-system thus it can be used to monitor the system.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x07
4	uint8_t	Message sub-ID	0x01
5	uint16_t	Payload length	16
6	uint16_t	IMU message count
7	uint16_t	GNSS message count
8	uint16_t	PPS count
9	uint16_t[5]	Reserved
10	uint8_t	Checksum A
11	uint8_t	Checksum B

7. External Event Messages¶

This section defines messages that users can send to the system to improve the navigation performance.

7.1. Zero Velocity Update Event¶

The user can send zero velocity update (ZUPT) messages when the vehicle is not moving. Especially, this will improve the navigation system where the GNSS signal is degraded. For the ZUPT message to be effective, it shall be sent at a rate higher than 2 Hz (recommended rate is 3 Hz).

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x09
4	uint8_t	Message sub-ID	0x01
5	uint16_t	Payload length	4
6	uint16_t	Horizontal Standard Deviation	mm/s (0: Invalid)
7	uint16_t	Vertical Standard Deviation	mm/s (0: Invalid)
8	uint8_t	Checksum A
9	uint8_t	Checksum B

7.2. Static Heading Event¶

This message can be used to initialize the inertial navigator when the position is available from the GNSS receivers but the heading initialization has difficulties due to degraded GNSS signals. For this message to be effective, it shall be sent at a rate higher than 2 Hz (recommended rate is 3 Hz).

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x09
4	uint8_t	Message sub-ID	0x02
5	uint16_t	Payload length	5
6	int16_t	Heading	0.01 degrees
7	uint16_t	ZUPT RMS	mm/s (0: Invalid)
8	uint8_t	Heading RMS	0.1 deg (0: Invalid)
9	uint8_t	Checksum A
10	uint8_t	Checksum B

7.3. Static Geo-Pose Event¶

This message can be used to initialize or aid the inertial navigation system when GNSS signals are not available. For this message to be effective, it shall be sent at a rate higher than 2 Hz (recommended rate is 3 Hz).

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x09
4	uint8_t	Message sub-ID	0x03
5	uint16_t	Payload length	32
6	double	Latitude	deg
7	double	Longitude	deg
8	float	Ellipsoidal height	m
9	int16_t	Roll	0.01 degrees
10	int16_t	Pitch	0.01 degrees
11	int16_t	Heading	0.01 degrees
12	uint16_t	Position RMS	cm (0: Invalid position)
13	uint16_t	ZUPT RMS	mm/s (0: Invalid)
14	uint8_t	Heading RMS	0.1 deg (0: Invalid)
15	uint8_t	Flags	See Note 1
16	uint8_t	Checksum A
17	uint8_t	Checksum B

Note

The first LSB (0x01) is used to denote the validity of the roll and pitch; the second LSB (0x02) is used to disable GNSS measurements.

7.4. Wheel Speed Event¶

Users can input a wheel speed of their vehicle to improve the navigation performance. For this message to be effective, it shall be sent at a rate higher than 2 Hz.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x09
4	uint8_t	Message sub-ID	0x04
5	uint16_t	Payload length	15
6	double	Time	seconds
7	float	Speed	m/s
8	uint16_t	Speed RMS	mm/s (0: Invalid speed)
9	uint8_t	Flags	See Note 1
10	uint8_t	Checksum A
11	uint8_t	Checksum B

Note

Usage of flags.

8. System Configuration Messages¶

This chapter describes the messages to get the information about the system or to configure the system without using the control software.

8.1. Antenna Separation¶

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x06
4	uint8_t	Message sub-ID	0x06
5	uint16_t	Payload length	04
6	uint8_t	Message type of the request
7	uint8_t	Message sub-ID of the request
8	uint8_t	Response	1: ACK, 2: NACK
9	uint8_t	Reserved
10	uint8_t	Checksum A
11	uint8_t	Checksum B

8.2. User Configuration Setup¶

Send the following message to request the product ID.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x06
4	uint8_t	Message sub-ID	0x0B
5	uint16_t	Payload length	0x01
6	uint8_t	Topic	0x01
7	uint8_t	Checksum A
8	uint8_t	Checksum B

8.3. Antenna Separation¶

This message sets the separation between two antennas, which will aid the ambiguity resolution for the attitude determination.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x06
4	uint8_t	Message sub-ID	0x0D
5	uint16_t	Payload length	8
6	uint8_t	Topic	0x07
7	uint8_t	Antenna ID 1	0x00
8	uint8_t	Antenna ID 2	0x01
9	uint8_t	Reserved
10	float	Separation	m
11	uint8_t	Checksum A
12	uint8_t	Checksum B

8.4. User Configuration Setup¶

This message is used to setup the user configuration which controls the behavior of the navigator. The system will respond with the message in Section 8.1. For this to take effect, the user needs to restart the system after sending this message.

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x06
4	uint8_t	Message sub-ID	0x0D
5	uint16_t	Payload length	\(93+12n_{A}+2n_{M} or 114+12n_{A}+2n_{M}\)
6	uint8_t	Topic	0x0A
7	uint8_t	Aiding sensor indicators	See Note 1
8	uint8_t	Flags	See Note 2
9	uint8_t	Number of User ICD messages to configure ( \(n_{M}\))
10	uint8_t	Minimum GNSS velocity for heading initialization	m/s
11	uint16_t	Maximum dead-reckon time; the system will stop outputting the navigation solution if the dead-reckoning time exceeds this limit.	seconds
12	uint16_t	Maximum Nav Output Rate	0.1 Hz
13	double[3][3]	IMU to user-frame rotation matrix ( \(C_{IMU}^{b}\) )	In row-major order
14	int32_t[3]	Output position offset	1.0e-4 m
15	int32_t[ \(n_{A}\)][3]	GNSS antenna lever arm in the user body frame	1.0e-4 m
16	User ICD message configuration block; exists only if \(n_{M} > 0\) .		See Note 3
17	DMI configuration block; exists only if the DMI bit is set in the aiding sensor indicators.		See Note 4
18	uint8_t	Checksum A
19	uint8_t	Checksum B

Note

Aiding sensor indicators:

Bits	Usage
1-2	Number of GNSS antennas (nA)
3	DMI exists
4-8	Reserved

Usage of flags:

Bits	Usage
1	Initialize heading from GNSS velocity; to activate this option the x-axis of the user body frame must be aligned with the forward direction of the vehicle.
2	Enable static position pinning; the system will output a fixed position during a static period detected by the GNSS. Note that there is a chance that the system can miss the detection if the signal quality becomes bad.
3	If set the entered GNSS antenna lever-arm is w.r.t. the IMU housing mark; otherwise it is w.r.t. the center of the IMU.
4	If set the entered output position lever-arm is w.r.t. the IMU housing mark; otherwise it is w.r.t. the center of the IMU.
5	If set the entered DMI antenna lever-arm is w.r.t. the IMU housing mark; otherwise it is w.r.t. the center of the IMU.
6-8	Reserved

User ICD message configuration block; care needs to be taken when choosing high-rate outputs as outputting multiple high-rate messages can saturate the communication port.

Field	Type	Description	Content
1	uint8_t	Sub-ID for message 1	See Section 5
2	uint8_t	Port ID for message 1	See below for port ID definition
3	…
4	uint8_t	Sub-ID for message nM	See Section 5
5	uint8_t	Port ID for message nM	See below for port ID definition

Port ID	Definition
0x00	Invalid, the output is turned off
0x01	Ethernet
0x02	UART0
0x04	UART1
0x80	Internal Log

DMI configuration block:

Field	Type	Description	Content
1	uint8_t	DMI ID	0: Invalid, otherwise valid
2	double	DMI scale factor	pulse/m
3	int32_t[3]	DMI lever-arm	1.0e-4 m

8.5. User Configuration Query¶

The system will send the current configuration if it receives the following message:

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x06
4	uint8_t	Message sub-ID	0x0B
5	uint16_t	Payload length	0x01
6	uint8_t	Checksum A
7	uint8_t	Checksum B

The format of the response will be the same as the one in Section 8.4 except that the message sub-ID is 0x0C. If it fails to read the stored configuration, it will respond with the message in Section 8.1 with NACK.

8.6. IP Address of the System¶

Users can query the IP address of the system by sending the following message:

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x06
4	uint8_t	Message sub-ID	0x0B
5	uint16_t	Payload length	0x01
6	uint8_t	Topic	0x0B
7	uint8_t	Checksum A
8	uint8_t	Checksum B

If the Ethernet port is connected, the system will respond with the following message:

Field	Type	Description	Content
1	uint8_t	Sync 1	0xAF
2	uint8_t	Sync 2	0x20
3	uint8_t	Message type	0x06
4	uint8_t	Message sub-ID	0x0C
5	uint16_t	Payload length	0x05
6	uint8_t	Topic	0x0B
7	uint8_t[4]	IP Address
8	uint8_t	Checksum A
9	uint8_t	Checksum B

If the port is not connected the system will send out an NACK message in Section 8.1 with the ‘Reserved’ field 0x0B.

9. CANBUS Messages¶

Defined in this section are the messages to be sent through the CANBUS.

9.1 Message ID 0x001¶

This message contains the system time of the navigation data.

Field	Type	Description	Content
1	uint32_t	Seconds
2	uint32_t	Nano seconds

9.2 Message ID 0x002¶

This message contains the GPS seconds of the week of the navigation message.

Field	Type	Description	Content
1	uint32_t	Seconds
2	uint32_t	Nano seconds

9.3 Message ID 0x003¶

This message contains the horizontal position of the vehicle.

Field	Type	Description	Content
1	int32_t	Latitude	\(10^{-7}\) deg/bit
2	int32_t	Longitude	\(10^{-7}\) deg/bit

9.4 Message ID 0x004¶

This message contains the horizontal velocity.

Field	Type	Description	Content
1	int32_t	Velocity in North	\(10^{-4}\) m/s
2	int32_t	Velocity in East	\(10^{-4}\) m/s

9.5 Message ID 0x005¶

This message contains the vertical position and velocity.

Field	Type	Description	Content
1	int32_t	Ellipsoidal height	\(10^{-4}\) m
2	int32_t	Velocity in Down	\(10^{-4}\) m/s

9.6 Message ID 0x006¶

This message contains the roll and pith of the vehicle.

Field	Type	Description	Content
1	int32_t	Roll	\(10^{-6}\) deg
2	int32_t	Pitch	\(10^{-6}\) deg

9.7 Message ID 0x007¶

Field	Type	Description	Content
1	int32_t	Heading	\(10^{-6}\) deg
2	uint16_t	GPS week number
3	uint8_t	Alignment status	0: Invalid, 1: Coarse, 2: Fine
4	uint8_t	Roll, pitch heading status	0: Invalid, 1: Valid

9.8 Message ID 0x008¶

This message contains x-components of the corrected IMU data.

Field	Type	Description	Content
1	int32_t	Acceleration X-axis	\(10^{-6}\) m/s2/bit
2	int32_t	Rotation rate in X-axis	1/360000 deg/bit

9.9 Message ID 0x009¶

This message contains y-components of the corrected IMU data.

Field	Type	Description	Content
1	int32_t	Acceleration Y-axis	\(10^{-6}\) m/s2/bit
2	int32_t	Rotation rate in Y-axis	1/360000 deg/bit

9.10 Message ID 0x00A¶

This message contains z-components of the corrected IMU data.

Field	Type	Description	Content
1	int32_t	Acceleration Z-axis	\(10^{-6}\) m/s2/bit
2	int32_t	Rotation rate in Z-axis	1/360000 deg/bit

9.11 Message ID 0x101¶

This message contains the system time of the raw IMU data.

Field	Type	Description	Content
1	uint32_t	seconds	seconds
2	uint32_t	Nano seconds

9.12 Message ID 0x101¶

This message contains x-axis components of the raw IMU data.

Field	Type	Description	Content
1	int32_t	Acceleration X-axis	\(10^{-6}\) m/s2/bit
2	int32_t	Rotation rate in X-axis	1/360000 deg/bit

9.13 Message ID 0x0103¶

This message contains y-axis components of the raw IMU data.

Field	Type	Description	Content
1	int32_t	Acceleration Y-axis	\(10^{-6}\) m/s2/bit
2	int32_t	Rotation rate in Y-axis	1/360000 deg/bit

9.14 Message ID 0x0104¶

This message contains z-axis components of the raw IMU data.

Field	Type	Description	Content
1	int32_t	Acceleration Z-axis	\(10^{-6}\) m/s2/bit
2	int32_t	Rotation rate in Z-axis	1/360000 deg/bit

10. Tips for System Usage¶

If a laptop computer’s display is too close to a GNSS antenna, it can cause adverse effects on the navigation system due to jamming/interference.

_images/Laptop_computer_jamming_the_GNSS.png

Figure 5: Laptop computer jamming the GNSS