FAQ

General:

Navigation Filter:

External Measurements:

Support

Software:

Miscellaneous:

 

General

 

Do settings get erased from the 3DM-CV7 if I unplug it?

  • It depends. The 3DM-CV7 will use the existing "startup settings” stored in the device unless the settings are saved prior to power down. To save the settings, do one of the following:
    • In SensorConnect, click “Save as Startup Settings” in the “Save/Load” tile.
    • In SensorConnect, click the checkbox “Save as Startup Settings” in the “Streaming” tile.
    • In ROS, set the "save_settings" param to true and successfully launch the node
    • In MSCL, use the node.saveSettingsAsStartup() function.
    • Use the Device Settings (0x0C,0x30) command with the SAVE function selector.
  • In SensorConnect, you can also export a .json settings file to your local computer that will save your full device configuration, which can be loaded again in the future.

 

How do I upgrade firmware?

  • Please see the Firmware Upgrades page for methods and instructions on upgrading device firmware.

 

Navigation Filter

 

Why is the filter stuck in Vertical Gyro Mode? 

  • The filter is likely stuck in Vertical Gyro Mode because it does not have sufficient initial conditions. See Filter States for more info on Vertical Gyro Mode.
  • In Vertical Gyro Mode, the Navigation Filter is only reporting valid gyro stabilized pitch, roll, and the change in heading relative to the initial orientation. To transition to Full Navigation mode, the Navigation Filter requires the initial conditions for all states shown in the table below. These can be provided to the Navigation Filter through the Initialization Configuration (0x0D,0x52) command. The time to transition from power on to Full Navigation mode under ideal conditions is typically less than 3 seconds.
Filter Mode Filter State Value Initial Conditions Required Available Outputs
Initialization 1 None None
Vertical Gyro 2 Roll, Pitch (from IMU) Roll, pitch, relative heading
AHRS 3 Absolute heading Roll, pitch, absolute heading
Full Navigation 4 Absolute heading, initial position, initial velocity Roll, pitch, absolute heading, position, velocity

 

How do I improve Navigation Filter performance?

The time to transition to the Full Navigation filter mode is less than 3 seconds under ideal conditions. The following tips commonly resolve cases where convergence takes longer than expected:

  • Ensure that your firmware is updated to the latest version.
  • Ensure antennas are correctly installed, and if using dual antenna, that their offsets are not accidentally swapped (a common problem).
  • Ensure the proper Filter Aiding Measurements are enabled.

 

How do I know when I can trust the Navigation Filter solution?

It is highly recommended to read the Navigation Filter section of the manual. You will need to configure the device to stream the data fields that contain the status information required for your application. Upon receipt of the status fields, you will need to set thresholds for the data based on your application's requirements, for example: 

  • The Status (0x82,0x10) message provides two important pieces of information for the user: the current Filter State (AKA mode) and Status Flags that provide real-time warnings about the filter's condition and its estimates.
    • The Status (0x82,0x10) message will report values of 4, 1, 1, when the Navigation Filter is in normal operation. These numbers correspond to Full Navigation Filter State, Default Dynamics Mode, and Converged filter Status Flags.
    • See "Interpreting the Status data channel" below for more info.
  • Filter Position Uncertainty Messages
    • The user must decide what position uncertainty values are required for their application. Typical 1σ values are:
      • Single point: 1.25-2.5m
      • RTK-Float: 0.1- 0.8m
      • RTK-Fixed: 0.01 - 0.06m (error model assumes maximum base station baseline of 50 km)
    • Position uncertainty is available in different frames in the following messages:
  • Euler Angles Uncertainty (0x82,0x0A)
    • Set application specific Yaw (heading) uncertainty threshold
    • Verify uncertainty is below threshold
  • Aiding Measurement Summary (0x82,0x46)
    • Verify selected Aiding Measurements are reflected in the output as enabled, used, and ideally not reporting any errors.
    • This is easily monitored in SensorConnect.

 

How do I interpret the Status (0x82,0x10) message?

The data fields reported by the Status (0x82,0x10) message are the Filter State, Dynamics Mode, and Status Flags. The Status Flags is a bitfield that must be properly interpreted:

  • SensorConnect's Status QuickView performs the conversion for the user into easy to understand text.
  • The ROS drivers  RQT Status QuickView GUI performs the conversion for the user into easy to understand text.
  • If converting manually, a simple online decimal to binary converter or calculator application in "programmer mode" will work.
  • For embedded applications, a simple bitshift calculation is required.
  • We recommend the user checks for the Filter state = 0x04 and Status flags = 0x01 or 0x02 (i.e. no warnings are raised and the filter condition is either stable or converging) at minimum to verify satisfactory filter performance.

Ex: What does 4, 1, 1025 mean from Status (0x82,0x10)? 

  • One can use any decimal to binary converter, we see the 0th and 10th bit have values of 1.
  • The 0th and 1st bits correspond to the Filter Condition,as described on the Filter Status Flags page. The 0th bit indicates a Filter condition of Stable. This is desired so is not the cause of concern.
  • The 10th Status Flag bit corresponds to a time sync warning as seen in the table below with the 10th bit's row highlighted in yellow. This means no PPS source is detected and the recommended action is to check the PPS source is set correctly i.e. ensure an antenna is connected for the PPS source selected.

 

Bit # Bit Value Description Potential Cause Recommended Action
0-1 1 Filter condition (Stable/Converging/Unstable) Insufficient initial conditions supplied. Verify required conditions are properly enabled. Review Filter States.
2 0 Roll/Pitch Warning Sensor is not aligned with vehicle frame. Review Vehicle Frame page.
3 0 Heading Warning Heading source is not valid. For Dual Antenna: Multipath, EMI, incorrect antenna offsets. For Magnetometer:time varying magnetic interference. For Magnetometer:perform Magnetometer Calibration, check for time varying magnetic interference via Scaled Mag (0x80,0x06), if present use external heading measurement.
4 0 Position Warning Multipath, EMI, incorrect antenna offsets, antennas obstructed, antenna cable shorted. Review How to improve filter performance above. Review: Antenna offsets, FAQ: Antenna sections, FAQ:How to improve filter performance.
5 0 Velocity Warning    
6 0 IMU Bias Warning Gyro bias is high. Perform Capture Gyro Bias (0x0C,0x39)
7 0 GNSS Clock Warning Multipath, excessive vibration. Not critical concern - continue navigation.
8 0 Antenna Lever Arm Warning Antenna Lever Arm offsets are likely incorrect. To improve performance, review Antenna(s) page.
9 0 Mounting Transform Warning Transform is likely incorrect. Review Vehicle Frame page.
10 1 Time Sync Warning No PPS source detected. Check PPS source is set correctly i.e. GNSS receiver 1 = PPS 1
12-15 0 Solution Error Filter computation warning flags. If any bits 12-15 are set, all filter outputs will be invalid. Reset Navigation Filter (0x0D,0x01)

 

  • Note: the filter condition occupies 2 bits (bits 0 and 1) and can be interpreted as shown below (see Filter Status Flags page for more info).
Filter Condition Values Description
1 Stable
2 Converging
3 Unstable/Recovering

 

Can the 3DM-CV7 navigate during a GNSS outage?

  • Yes, the 3DM-CV7-INS was designed with GNSS denied operation in mind. Although the 3DM-CV7 must have entered Full Navigation Mode (Filter Mode 4) prior the outage. If the 3DM-CV7 initially has a GNSS lock and experiences an outage, it will continue to provide a PVAT (Position, Velocity, Attitude, Time) solution throughout the outage.
  • In cases where outages longer than 60 seconds are expected, and depending on the position accuracy requirements of the application, we typically recommend using additional Filter Aiding Measurements .
  • For UAS and USV higher uncertainties may be allowable in which case the user may continue to navigate without these aiding measurements, while monitoring the navigation solution as described above. The 3DM-CV7 can continue to navigate but its position error will increase exponentially, as is the case on the majority of INS systems.

 

Yes, the 3DM-CV7-INS 's Navigation Filter can accept LIDAR, Radar, or Pitot measurements as long as they are pre-processed and input via the Body Frame Velocity (0x13,0x2A) aiding command or appropriate command in ROS, PX4 or ArduPilot. Providing accurate external body frame velocity measurements can greatly help the Navigation Filter during GNSS denied events as outlined in this white paper: Enhancing Inertial Navigation System Performance with Radar. See the Aiding Sensors page for more information and example code.

I don’t have a wheel odometry hardware encoder but I have and want to provide a speed measurement to the 3DM-CV7. Is this possible? 

Yes, the 3DM-CV7-INS 's Navigation Filter can accept speed measurements as long as they are pre-processed and input via the Body Frame Velocity (0x13,0x2A) aiding command. Providing accurate external body frame velocity input can greatly help the Navigation Filter during GNSS outage events as outlined in this white paper: Enhancing Inertial Navigation System Performance with Radar. See the Aiding Sensors page for more information and example code.

  • Uncertainty must be provided and can be determined through one of the following methods: 

    1. Datasheet Value:

      1. Read uncertainty specification from speed sensor datasheet.

    2. System Identification:

      1. If uncertainty is not provided, then drive the vehicle at constant speed and record data.

      2. Next, calculate variance and use 1σ variance as the uncertainty. The intent is to characterize the noise of the speed measurement.

      3. The speed selected should be the most common speed for the vehicle application.

      4. If the speed varies for the application, then this process should be repeated for the most common speeds.

    3. Empirical Filter Tuning:

      1. If methods 1 and 2 are not feasible, then the user must make an educated guess and tune speed uncertainty with multiple runs to observe how the filter performs.

      2. You are welcome to reach out to our Support team for assistance in this tuning.

Data

 

Is the bias removed from Compensated Angular Rate (0x82,0x0E) and Compensated Acceleration (0x82,0x1C) data channels?

Yes, but the Compensated Angular Rate or Compensated Acceleration messages are not anti-aliased at this time. This means, if you choose a sample rate lower than 500 Hz, aliasing can occur, which looks like noise but is actually due to down-sampling. This shortcoming is being addressed in the next firmware release.

 

Support

 

How do I obtain Engineering Support for my device ?

MicroStrain Support Engineers can be contacted through many methods. Please review the Support page for more information.

 

Software

 

Do you have data visualization tools?

  • Yes. You can setup a real-time data visualization dashboard in SensorConnect as shown below. You can also export this data as a CSV file for easy data processing, or to a binary file.

    •  

    Does MicroStrain by HBK have ROS drivers?

    Yes, and we have examples, and a dedicated ROS Engineer to support them and support you! See the Software page for more information.

    Does MicroStrain by HBKhave PX4 drivers? 

    Yes! Please see the Software page for more information.

    Does MicroStrain by HBKhave ArduPilot drivers? 

    Yes! Please see the Software page for more information.

    Does the 3DM-CV7-INS support NMEA input? 

    Yes! The 3DM-CV7-INS provides direct NMEA input on a dedicated port to simplify the integration process. Please see the NMEA Input page for more information and the NMEA Input with Ublox F9P application note for a detailed, step by step guide.