Swift Duro Inertial User manual

Duro Inertial User Manual
Version 2
2022-07-13
Supported Platforms
Platform
Duro Inertial
Firmware
≥ 2.1.21
Overview
Duro Inertial is a ruggedized version of Swift Navigation’s Piksi® Multi dual-frequency Real Time Kinematics (RTK) GNSS
receiver including inertial sensor fusion algorithm, which combines GNSS and inertial measurements into an unified
solution. The combination of GNSS and inertial measurements allows Duro Inertial to provide highly-accurate, continuous
position solutions during brief GNSS outages and to deliver robust precision navigation solutions in harsh GNSS
environments.
This document describes Duro Inertial with firmware version 3.0.
The INS settings and IMU sensors alignment process have significantly changed between firmware versions 2.4 and 3.0.
For the older firmware use Duro Inertial User Manual v1 (UM-110008-01).
About this Manual
Every effort has been taken to ensure the accuracy of the contents of this manual. This manual is based on Duro Inertial
firmware version 3.0.11. In case of differences between the manual and the product, use the information from the
product.
Prerequisites
This document describes the installation, configuration, and operation of features specific to Duro Inertial. Users should
be familiar with the information contained in the Duro User Manual before following this guide.
Duro User Manual - https://www.swiftnav.com/latest/duro-user-manual

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Table of Contents
Overview 1
About this Manual 1
Prerequisites 1
Table of Contents 2
System Architecture 3
Installation 3
GNSS Antenna Mounting 3
Duro Inertial Mounting 4
Antenna Offset 5
Vehicle Frame Orientation 7
Configuration 7
Firmware Version 7
Default Configuration 7
Firmware Settings 8
IMU Settings 9
INS Settings 9
Other Settings 10
RTK Corrections 11
Operation 11
Alignment Process 11
LED Indicators 12
Device Data Output 13
SBP Messages 13
NMEA Messages 14
Known Issues 15
Appendix A - Identifying Duro Inertial 15
Appendix B - Duro Inertial Orientations 16
Appendix C - Duro Inertial Installation Worksheet 18
Appendix D - Device and Vehicle Frames 19
Glossary 20
Additional References 21
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System Architecture
Typical Duro Inertial system setup is shown on the diagram depicted below. The product is able to combine real time
GNSS observables from a base and a rover as well as motion sensed by the MEMS IMU in the product into one Fused RTK
GNSS + INS position, velocity, attitude, and time solution (PVAT).
Figure 1: Duro Inertial system architecture
Installation
For proper Duro Inertial operation it is essential to mount both the Duro Inertial and the GNSS antenna securely and firmly
to the vehicle body. During operation, the antenna and Duro Inertial must remain in the same position relative to each
other (i.e., both must be mounted on the same frame).
GNSS Antenna Mounting
For the best signal reception, mount the GNSS antenna on a stable structure located away from other antennas and
devices.
The GNSS antenna should be mounted completely externally. Do not place the GNSS antenna inside, or partially inside, of
a housing or vehicle.
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The GNSS antenna should have the best achievable sky view, in all directions, down to the horizon. Do not shield or
occlude any portion of the antenna.
The GNSS antenna is sensitive to its environment. Since producing high-accuracy GNSS position solutions requires
tracking carrier phase information from satellites, it is much more sensitive to obstructions than standard consumer
GNSS receivers (like those found in smartphones and handhelds).
All antenna offset measurements should be taken to the phase center of the GNSS antenna.
Duro Inertial Mounting
In order to properly detect motion, Duro Inertial must be securely and firmly mounted to the vehicle. Mounting Duro Inertial
on the vehicle centerline is recommended.
To maximize sensor sensitivity, mounting Duro Inertial in an orientation orthogonal to the vehicle body is recommended.
This means that Duro Inertial should be mounted with all three axes forming angles in multiples of 90° (0°, 90°, 180°,
270°), with respect to the primary direction of vehicle motion. For easier installation and setup, it is recommended to align
the X axis direction of the Duro Inertial with the primary direction of vehicle motion.
Duro Inertial must be rigidly mounted to the body of the vehicle. Any vibration which is not directly related to vehicular
motion will degrade the quality of the inertial data. Installing Duro Inertial on a flexible vehicle rooftop, engine cover, or
fender - where the mounting surface can flex and vibrate independently of the vehicle body - should be avoided. Similarly,
placing the sensor on plush seating of a vehicle with the antenna on the rigid part of the vehicle will yield poor results.
Ensure that the Duro Inertial enclosure is on the same rigid body as the GNSS antenna. Some suspension systems may
isolate the chassis from the cab and if the antenna moves when the Duro Inertial does not it will degrade results. When
installing the device inside a vehicle, directly mounting it to the vehicle chassis is recommended. Ideally, Duro Inertial
should be mounted rigidly to the vehicle’s inertial mass, directly above the center of rotation (i.e the pivot point).
A straightforward approach to installing Duro Inertial is to mount it on a rigid surface, located on the top of the vehicle,
with the GNSS antenna attached to the receiver using an included bracket. This approach is demonstrated in Figure 2.
Mounting the GNSS antenna directly on the top of the receiver improves performance and makes setup easier. In this
configuration, there is no need to measure the antenna lever arm - the default antenna offset settings can be used.
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Figure 2: Duro Inertial sample installation
If it is impractical to mount the entire Duro Inertial system on the top of a vehicle, mounting the Duro Inertial enclosure and
GNSS antenna to the same rigid body, while minimizing the distance between them, is recommended. Ideally, the GNSS
antenna should be mounted directly above Duro Inertial - with the antenna and enclosure both mounted on the vehicle
centerline. On passenger vehicles, practical mount points for the Duro Inertial enclosure may include: the spare tire bay,
the seat support rails, and the floor of the vehicle chassis.
Antenna Offset
After installing the GNSS antenna and Duro Inertial on the vehicle, the antenna offset needs to be measured. The antenna
offset consists of X, Y, and Z components which should be measured along Duro Inertial’s X, Y, and Z axes (i.e. within the
device frame) from Duro to the antenna. The “Device Frame” is the reference frame aligned with the markings on the Duro
Inertial enclosure. These values will need to be provided to the device firmware settings during the configuration step.
On Duro Inertial, the device frame reference point is the intersection of the reference mark from the top of the enclosure
and the bottom surface of Duro Inertial (see Figure 3). The orientation of the device frame is shown in Figure 4. Note, the
Z-axis is defined to be in the “down” direction.
FIgure 3: Device Frame Reference Point (dimensions in millimeters)
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Figure 4: Device Frame Orientation
Distance value in the marked direction of the axis will have a positive sign. The value in the opposite direction will have a
negative sign. Distances should be measured in meters, with 1 cm accuracy, from the Duro Inertial reference point to the
phase center of the GNSS antenna.
The phase center of the GPS500 GNSS mini-survey antenna included in the Duro Inertial Starter Kit is located at the center
of the antenna, 50 mm above the bottom of the antenna mount (middle point between L1 and L2 phase centers).
Figure 5: GPS500 mini-survey antenna phase center location.
Use the Duro Inertial Vehicle Profile Worksheet provided in Appendix C to write down antenna offset measurements taken
on the vehicle for future reference.
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Vehicle Frame Orientation
In addition to the antenna offset, the vehicle frame orientation should be measured. Entering proper orientation to the
Duro Inertial firmware settings is essential for a correct navigation output.
To obtain yaw, pitch, and roll angles for the orthogonal mounting, refer to Appendix B - Duro Inertial Orientations, and use
the values which match your installation. One way to think of the vehicle frame orientation is the rotations required to
make the axis of the vehicle frame align with the axis marked on Duro.
Use the Duro Inertial Vehicle Profile Worksheet provided in Appendix C to record vehicle frame orientation values for future
reference. The vehicle frame, and the pitch roll and yaw orientation directions, are defined according to the diagram below,
where z is defined into the page (down).
Figure 6: Vehicle Frame definition
Configuration
For proper operation, and the best performance, Duro Inertial firmware needs to be configured correctly. Duro Inertial has
all applicable settings for Piksi Multi and Duro in addition to the Duro Inertial specific settings in the “ins” (inertial
navigation system) settings grouping. Follow the instructions below to setup Duro Inertial firmware.
Firmware Version
Duro Inertial requires Piksi Multi firmware v2.1.21 or newer. The latest firmware can be downloaded from the Swift
Navigation Support portal (https://support.swiftnav.com).
Default Configuration
By default, Duro Inertial is configured to be used with the Swift GNSS mini-survey antenna mounted directly to the Duro
Inertial enclosure and with X axis pointing forward. However, the INS fusion output is disabled by default to avoid
outputting position solutions from a possibly incorrectly configured system.
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To view IMU and INS configuration:
●Connect to Duro Inertial via Swift Console
●Select the Settings tab
●Locate the IMU and INS settings group
Figure 7: Duro Inertial IMU and INS settings
Firmware Settings
There are a number of firmware settings which directly affect the behavior of Duro Inertial. These are detailed in the tables
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below. Device settings can be configured via Swift Console on the Settings tab or directly via SBP messages.
IMU Settings
IMU settings control range and output rate from inertial sensors.
Settings Group: imu
Name
Units
Accepted Values
Default Value
Description
acc_range
g
2, 4, 8, 16
8
Acceleration sensor range.
gyro_range
deg/s
125, 250, 500, 1000, 2000
125
Angular rate sensor (gyroscope) range.
imu_rate
Hz
25, 50, 100, 200
100
IMU raw output data rate.
imu_raw_output
n/a
True, False
False
Enable/Disable IMU raw data output.
Notes
●Gyroscope and Accelerometer ranges (acc_range,gyro_range) should be adjusted for the dynamics of your
application. In order to maintain the highest resolution of measurements, choose the smallest range which
encompasses the dynamics of your application. However, keep in mind that your application may involve sudden,
maximum dynamic changes which may not be typical or anticipated. These maximums should be used when
selecting a scale for both accelerometer and gyroscope ranges.
●Duro Inertial does not use the magnetometer sensor and therefore the mag_raw_output and mag_rate parameters
do not need to be set.
●In order to use inertial navigation, imu_raw_output must be enabled and imu_rate must be set to 100 Hz.
●Remember to click the Save on Device button on the Swift Console Settings tab to store new values on the device.
INS Settings
INS settings control inertial navigation sub-system operation.
Settings Group: ins
Name
Units
Accepted Values
Default Value
Description
antenna_offset_x
m
0
Distance along Duro Inertial X-axis from the
reference point to the antenna phase center
antenna_offset_y
m
0
Distance along Duro Inertial Y-axis from the
reference point to the antenna phase center
antenna_offset_z
m
-0.127
Distance along Duro Inertial Z-axis from the
reference point to the antenna phase center
antenna_offset_deviation
m
> 0
0.05
Standard deviation of antenna lever arm
measurement. Must be greater than 0. This value
should overestimate the actual expected error.
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Settings Group: ins
dr_duration_max
s
>= 0
600
Sets the maximum duration for which the inertial
system will dead reckon
dr_timeout_pos_stddev
m
> 0
20
Maximum estimated standard deviation of the
INS position for which the inertial system will
dead reckon
fused_soln_freq
Hz
1, 2, 5, 10, 20
10
Fusion engine output data rate. This value can be
different from the GNSS output rate (soln_freq).
output_mode
Disabled,
Loosely Coupled
Disabled
Sets the operation mode of the inertial
navigation system. Use Loosely Coupled mode
to enable INS operation.
vehicle_frame_pitch
deg
-180 .. 180
0
Pitch angle representing rotation from vehicle
frame to device frame. Rotations are performed
extrinsically in the order roll, pitch, then yaw.
vehicle_frame_roll
deg
-180 .. 180
0
Roll angle representing rotation from vehicle
frame to device frame. Rotations are performed
extrinsically in the order roll, pitch, then yaw.
vehicle_frame_yaw
deg
-180 .. 180
0
Yaw angle representing rotation from vehicle
frame to device frame. Rotations are performed
extrinsically in the order roll, pitch, then yaw.
vehicle_frame_deviation
deg
> 0
1.0
Standard deviation of misalignment
measurement. Must be greater than 0. This value
should overestimate the actual expected error.
Notes:
●Enter antenna_offset_x/y/z and vehicle_frame_yaw/pitch/roll as they were measured after installation. The
worksheet in Appendix C is a useful tool for determining these values.
●It is required to restart the device after changing INS output_mode (Click the Save on Device button on the Swift
Console Settings tab to store new value before restarting).
●Additionally to the basic settings described above, the INS group contains several advanced settings that can be
used to tune the INS solution for the specific application.
●The INS settings have significantly changed between firmware v2.4 and 3.0. For the older firmware use Duro
Inertial User Manual v1 (UM-110008-01).
●Remember to click the Save on Device button on the Swift Console Settings tab to store new values on the device.
Other Settings
All other Duro Inertial settings (like ports, protocols, rates, etc.) are the same as a standard Duro GNSS-only receiver. Refer
to the Duro User Manual for details about configuring data ports, protocols, message rates, etc.
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RTK Corrections
For the most precise and accurate position output, Duro Inertial should operate in RTK mode. Select and configure an RTK
correction source in the same manner as a GNSS-only Duro. Refer to the Duro User Manual and support articles on the
Swift Navigation Support Portal (support.swiftnav.com) for details.
Operation
With the INS system enabled, Duro Inertial will provide enhanced position output, including Dead Reckoning (DR) mode.
Additionally, the contents of several messages will include status information about the INS.
Duro Inertial requires a valid GNSS solution to initialize (align) the inertial subsystem. After the first valid GNSS solution,
Duro Inertial needs to be driven forward to perform the IMU alignment before it’s able to aid GNSS in precise positioning
through challenging environments (like tree foliage and urban canyons) and to provide navigation solutions during brief
GNSS outages (such as overpasses and short tunnels).
Since the inertial sensors output drifts over time, resulting in decreased position accuracy, the DR mode operation is
time-limited by the dr_duration_max and dr_timeout_pos_stddev setting (see settings in the section above).
Alignment Process
The Duro Inertial needs to perform an alignment procedure before it can provide positioning assistance to the system. The
alignment process will begin once the following conditions are met:
1. The position standard deviation reported by the GNSS Engine is less than 30 m
2. The velocity standard deviation reported by the GNSS Engine is less than 1 m/s
3. Straight-line forward movement occurs at a speed above 5 m/s (18 km/h, or 12 MPH)
Alignment should typically complete within a distance of 20 to 50 m if the sky visibility remains good during the
initialisation phase.
Notes:
●The alignment and calibration constants are not retained through power cycles. Alignment process is required
after each device power up or reset.
●The v3.0 firmware requires alignment to be performed while driving forward. The INS fusion will produce an
incorrect output if alignment is done while driving in reverse direction.
●The minimum alignment speed is configurable by the alignment_cog_min_speed_meters_per_second setting.
Lowering the value decreases alignment accuracy so it should be kept as high as possible.
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LED Indicators
Duro Inertial uses front panel LEDs to indicate when the INS is operational and the output position is computed using both
GNSS and inertial subsystem. Purple lights for the POS LED indicate that INS is in use. Refer to the LED description table
below for detailed information.
Figure 8: Duro Inertial LED indicators
LED Description
LED Name
Color
State
Description
POWER
LED Off
Off
No power or voltage out of range
Green
Continuously on
Device receiving power
POS
LED Off
Off
No position, GNSS antenna not detected
Orange
Slow blinking
No position, antenna detected, no satellite signals received, INS
not initialized
Orange
Fast blinking
No position, receiving satellite signals, INS not initialized
Orange
Continuously on
Position valid, GNSS solution only, INS not initialized/used
Purple
Continuously on
Position valid, combined GNSS and INS solution
Purple
Blinking
Position valid, DR mode (no GNSS solution)
LINK
LED Off
Off
No incoming corrections, no Internet access
Red
Blinking
Incoming corrections, no Internet access
Red
Continuously On
Internet access available, no incoming corrections
Red
On with intermittent flashing
Internet access available, incoming corrections
MODE
LED Off
Off
No RTK
Blue
Blinking
Float RTK mode
Blue
Continuously on
Fixed RTK mode
Note: after power up POS, LINK and MODE LEDs will blink white indicating the boot up process is completed.
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Device Data Output
Duro Inertial is capable of providing output in Swift Binary Protocol (SBP) and industry standard NMEA 0183 protocol over
UART and Ethernet ports. When INS is enabled, messages in both protocols will provide additional data described below.
SBP Messages
The subset of Swift Binary Protocol messages directly related to Duro Inertial operation are highlighted in the tables
below. When using Duro Inertial, you may need to adjust the enabled_sbp_messages setting for the interfaces you use to
communicate with the device. This setting is a comma separated list of message IDs (in decimal) that will be emitted on
each interface. By default, the enabled_sbp_messages setting does not include any of the inertial-specific messages.
The following position mode values are reported in the “Fix Mode” field in the Status Flags (refer to the SBP protocol
specification for more information):
0 No fix
1 Single Point Position (SPP)
2 Differential GNSS (DGNSS)
3 Float RTK
4 Fixed RTK
5 Dead Reckoning
6 SBAS
Additionally, the “Inertial Navigation Mode” field will contain INS status:
0 INS was not used to compute position
1 INS was used to compute position
Position Messages
Message
Message ID
Notes
SBP_MSG_POS_LLH
522
SBP_MSG_POS_LLH_COV
529
Message is not enabled by default.
SBP_MSG_POS_ECEF
521
Message is not enabled by default.
SBP_MSG_POS_ECEF_COV
532
Message is not enabled by default.
SBP_MSG_POS_LLH_ACC
536
Message is not enabled by default.
Velocity Messages
Message
Message ID
Notes
SBP_MSG_VEL_NED
526
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Velocity Messages
SBP_MSG_VEL_NED_COV
530
Message is not enabled by default.
SBP_MSG_VEL_ECEF
525
Message is not enabled by default.
SBP_MSG_VEL_ECEF_COV
533
Message is not enabled by default.
Orientation Messages
Message
Message ID
Notes
SBP_MSG_ORIENT_EULER
545
Message is not enabled by default. Only produced when INS is
enabled.
Status Messages
Message
Message ID
Notes
SBP_MSG_INS_STATUS
65283
Message is not enabled by default. Only produced when INS is
enabled.
Refer to the SBP protocol specification for message content details.
NMEA Messages
Following NMEA 0183 messages contain Dead Reckoning status information. NMEA messages do not contain orientation
nor other INS specific information.
NMEA 0183 Messages
Message
Notes
GGA
Quality Indicator:
0 - No fix
1 - Single Point Position (SPP)
2 - DGNSS or SBAS
4 - Fixed RTK
5 - Float RTK
6 - Dead Reckoning
GLL
RMC
VTG
Mode Indicator:
N - No fix
A - Autonomous fix
D - DGNSS or SBAS
E - Dead Reckoning (Estimated)
F - Float RTK
R - Fixed RTK
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Known Issues
●Position Valid (PV, pin 17 on the AUX connector) does not go high during Dead Reckoning.
Appendix A - Identifying Duro Inertial
Duro Inertial receivers can be identified in following ways:
1. Duro Inertial has a product name and part number located on the bottom of the enclosure.
Product
Duro® Inertial
Duro®
Part Number
00759-01 and 00759-02
00522-01
product_id
“Duro Inertial”
“Duro”
2. The product_id read-only setting reflects the product ID. This setting exists in the system_info group in the settings
interface that can be accessed via the Swift Binary Protocol API or the Swift Console program.
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Appendix B - Duro Inertial Orientations
Use the pictures below to determine Duro Inertial orientation angles in your vehicle installation.
Angles are in degrees.
Yaw: 0
Pitch: 0
Roll: 0
Yaw: 90
Pitch: 0
Roll: 0
Yaw: 180
Pitch: 0
Roll: 0
Yaw: -90
Pitch: 0
Roll: 0
Yaw: 0
Pitch: 0
Roll: 180
Yaw: 90
Pitch: 0
Roll: 180
Yaw: 180
Pitch: 0
Roll: 180
Yaw: -90
Pitch: 0
Roll: 180
Yaw: 0
Pitch: 90
Roll: 0
Yaw: 0
Pitch: 90
Roll: -90
Yaw: 0
Pitch: 90
Roll: 180
Yaw: 0
Pitch: 90
Roll: 90
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Yaw: 0
Pitch: -90
Roll: 180
Yaw: 0
Pitch: -90
Roll: -90
Yaw: 0
Pitch: -90
Roll: 0
Yaw: 0
Pitch: -90
Roll: 90
Yaw: -90
Pitch: 0
Roll: -90
Yaw: 0
Pitch: 0
Roll: -90
Yaw: 90
Pitch: 0
Roll: -90
Yaw: 0
Pitch: 180
Roll: 90
Yaw: 90
Pitch: 0
Roll: 90
Yaw: 180
Pitch: 0
Roll: 90
Yaw: -90
Pitch: 0
Roll: 90
Yaw: 0
Pitch: 0
Roll: 90
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Appendix C - Duro Inertial Installation Worksheet
Print and use this form to record Duro Inertial installation details and measurements. Antenna offset and vehicle frame
rotation need to be entered to firmware settings for proper system operation.
General
Date
Vehicle Name
Duro Inertial S/N
Antenna Offset (measured along X/Y/Z axis of Duro after installation, from Duro to antenna)
X
Degrees
Y
Degrees
Z
Degrees
Deviation
Degrees
Vehicle Frame Rotation
Yaw (Z)
Degrees
Pitch (Y)
Degrees
Roll (X)
Degrees
Deviation
Degrees
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Appendix D - Device and Vehicle Frames
The three Euler-angle settings for configuring the Device frame orientation with respect to the vehicle frame orientation
represent three extrinsic rotations in the order roll, pitch, and yaw. For example, a rotation matrix that can be used to
rotate a vector from the device frame (i.e a velocity in the Duro Inertial frame X-direction) to the Vehicle Frame, can be
represented as follows:
Extrinsic rotations are defined as rotations about the body where the body does not move.
Similarly, the Quaternion and Euler angle output from the device describe the orientation of the Vehicle Body Frame with
respect to the Navigation frame in real time. The euler rotations should be applied intrinsically in the order yaw, pitch, and
roll in order to rotate from a frame aligned with the local-level NED frame to the vehicle body frame. Mathematically, it can
be shown that this description of the real time Euler angles is equivalent to an Extrinsic rotation in the order roll, pitch, yaw
to rotate the vehicle frame into the local level NED frame. The equations below can be used to relate the Euler angles
reported in MSG_ORIENT_EULER, to the Body velocities reported in MSG_VEL_BODY, to the Navigation velocities reported
in MSG_VEL_NED. The vehicle body frame is defined according to Figure 6.
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Glossary
Term
Description
Antenna Offset
Three-dimensional distance between Duro Inertial and GNSS Antenna
Device Frame
The reference frame aligned with the XYZ axis markings on Duro Inertial
DR
Dead Reckoning
Dead Reckoning
Position computation method where the current position is computed based on a prior
known position and an estimated movement
Firmware
Embedded software running on electronic device
Fix
Valid position
DGPS, DGNSS
Differential GPS/GNSS
GNSS
Global Navigation Satellite System mainly including GPS, GLONASS, BeiDou (BDS), and
Galileo satellite systems
IMU
Inertial Measurement Unit
INS
Inertial Navigation System
Lever Arm
Three-dimensional distance between Duro Inertial reference point and GNSS antenna phase
center
Loosely Coupled
Navigation technique that takes GNSS position data and combines it with inertial sensor
measurements for a unified output
MPH
Miles Per Hour
Phase Center
Point inside the GNSS antenna for which position is calculated
Piksi Multi
Swift Navigation RTK GNSS receiver module included in Duro Inertial
RTK
Real Time Kinematic
SBAS
Satellite Based Augmentation System
SBP
Swift Binary Protocol - Swift Navigation’s proprietary protocol
SPP
Single Point Position
Swift Console
Graphic User Interface (GUI) program providing visual representation of what's happening
inside Swift Navigation’s GNSS receivers. Console displays information and allows the user to
adjust the settings on the hardware. Available for Windows, macOS and Linux.
Tracking
Receiving signals from GNSS satellites
www.swiftnav.com
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