External Aiding Sensors

The Navigation Filter is designed to accept external Aiding Measurement data to help improve its navigation solution. The effectiveness of these aiding measurements is directly affected by the accuracy of the aiding measurement and the care that is taken when installing the aiding sensors. This page provides a brief overview of best practices when installing common aiding sensors and provides recommendations on field-testing approved models to simplify integration with the 3DM-CV7-INS.

 

GNSS Receivers and Antennas

GNSS aiding measurements are provided to the 3DM-CV7-INS from external GNSS receiver(s). Improper installation can lead to navigation solution errors in the 3DM-CV7-INS that can be difficult to debug. Follow the recommendations on the Antenna(s) page to ensure performance is maximized.

u-blox ZED-F9P

The u-blox ZED-F9P has been tested extensively as a GNSS aiding sensor for the 3DM-CV7-INS and provides great for performance for low SWAP-C, in a simple to use interface.

Single Antenna:

Example code is provided in our MIP SDK to simplify integration of this receiver with the 3DM-CV7-INS for a single antenna position, velocity, and time GNSS solution. It is important to configure the 3DM-CV7-INS for your application to ensure the device performs properly.

The ZED-F9P also can stream NMEA data on its UART ports which the 3DM-CV7-INS can directly parse from any of its GPIO ports, greatly simplifying the GNSS integration process. The NMEA Input page provides a high level overview of the steps to configure each device for this simple integration. Use of the MIP Aiding (0x13) command set will enable better navigation performance than the NMEA Input due to the GNSS uncertainties being updated dynamically instead of set statically at initialization, but may require more configuration.

 

Body Frame Velocity Sensors

The following aiding sensors can provide useful aiding measurements to the 3DM-CV7-INS via the Body Frame Velocity (0x13,0x2A) command.

Radar

MicroStrain's Robotics R&D group has performed extensive testing and found radar to be an effective and robust aiding sensor for ground vehicle applications. An example of this integration and the impressive 3DM-CV7-INS performance improvements during a GNSS outage has been published with example code in this white paper: Enhancing Inertial Navigation System Performance with Radar. This white paper provides example code using MicroStrain Inertial ROS driver, a custom ROS package for radar pre-processing, and configuration of a Ublox F9P.

When integrating a radar velocity sensor with the 3DM-CV7-INS, pre-process the velocity into a 3 element vector float format and provide the aiding measurement via the Body Frame Velocity (0x13,0x2A) command. An example of this can be found on the Filter Aiding Measurements page.

Pitot Tube

While the 3DM-CV7-INS does not natively accept air speed data, a pitot tube may be used in conjunction with other sensors to remove wind velocity to calculate the x-axis of the Body Frame Velocity (0x13,0x2A) command. Ensure to either provide Uncertainties of 0 m/s for the y and z-axes or set the Valid Flags to 0 for the same axes of the command.

Optical Flow

Optical Flow can be a useful aiding sensor for applications which are relatively close to the ground and wish to constrain their position error in the event that their GNSS signal becomes degraded or denied. The 3DM-CV7-INS does not natively accept optical flow sensor data, but can accept pre-processed data through the Body Frame Velocity (0x13,0x2A) command.

 

External Magnetometer

The 3DM-CV7-INS supports external magnetometer aiding to mitigate the magnetic interference errors ubiquitous on autonomous vehicle applications. When installing an external magnetometer, ensure to place it far away from potential magnetic interference sources to reduce or eliminate their effect. Examples of common magnetic interference sources are moving ferro-magnetic components like motors, robotic arms, fans etc. See the Filter Aiding Measurements for an example aiding command for external magnetometer input.

 

External Pressure Sensor

The 3DM-CV7-INS supports external pressure sensor aiding to enable the input of higher-accuracy static pressure sensors. This aiding measurement helps constrain altitude drift during GNSS denied environments. Ensure to install this sensor in a location on the vehicle where it is exposed to static atmospheric pressure, but avoid locations of high dynamic pressure ex: the leading edge of a high speed fixed wing drone, in the prop-wash of a quadcopter, etc.

 

NOTE: MicroStrain Support Engineers are always available to assist in sensor integration. See FAQ: Support for contact info.