Land

Mechanical installation

Land applications assume a 2D motion with (depending on the motion profile) limited to no lateral velocity. The INS sensor can be located anywhere in the vehicle, considering the following recommendations:

• Sensor is rigidly fixed to the vehicle frame
• Sensor is not moving in regard to other equipment (antennas, LIDAR, etc...)
• Sensor is far from vibrations sources.

Note

SBG Systems IMU are designed to handle vibrations without specific care. Nevertheless in case of highly vibrating environment, a mechanical vibration isolation might be required for proper operation. Silicon or wire dampers can be used for that purpose.

Vehicle Reference Frame

The vehicle coordinate frame is defined as follows:

• X axis points to the front of the car
• Y axis points rightward
• Z axis points downward.

Note

The sensor can be placed in any orientation in the vehicle. When IMU axes do not match exactly with the vehicle coordinate frame, the rough and fine alignment parameters should be corrected through the configuration interface to realign the IMU and vehicle coordinate frames.

Primary lever arm

Once the sensor is installed in the vehicle, the center of Rotation of the vehicle should be identified. This is most often located along the rear axle, at the ground level.

The Primary Lever Arm which is the signed distance in the vehicle frame, FROM the IMU, TO the Center of Rotation should be measured within a 5 cm accuracy.

GNSS setup considerations

When installing your INS with a GNSS aiding, you will need to install the GNSS antennas with a clear view of sky (usually on the roof of the vehicle), and fixed with respect to the IMU.

The GNSS lever arms shall also be measured, which are the signed distance, expressed in the vehicle coordinate frame, FROM the sensor center of measurements, TO the GNSS antenna.

We usually require these measurements to be precisely performed, within 1 cm accuracy.

Note

It's generally not practical to measure with such precision the lever arms, so SBG Systems developed lever arm calibration that enables you to measure rough lever arm estimation (10cm precision) and let the tool refine those measurements.

Single antenna installation

Single antenna installation is possible on all automotive applications with the only limitation that the heading will not be observed while stationary.

A single antenna installation with GNSS lever arm is shown below:

Dual GNSS antenna placement

Dual antenna may be required if dynamics are expected to be low during extended periods of time. When using the INS in a dual antenna setup, the heading will remain stable and precise in all conditions. Heading can also be initialized in static conditions.

Dual antenna systems installation will require special care in order to obtain optimal performance:

• The antennas must be fixed with respect to the to the inertial unit
• Same antenna type should be used
  
• Same cables with identical lengths must be used for both antennas. If splitters are used make sure that they are adapted and with the same characteristics
• If antennas are not permanently installed on the vehicle roof, antennas reference marks (usually the connector position) should be mounted in a repeatable fashion in order to guarantee antennas phase center stability from mount to mount and minimize changes to heading misalignment angle.
• Both antennas must have the same view of sky: typically place the antennas on the roof of the vehicle.
  
• Baseline of at least 1 meter between both antennas is recommended for best performance
• If the antenna model does not have integrated ground plane and is not placed on a metal roof, a 10 cm diameter ground plane must be added for both antennas.

Both GNSS antennas lever arms should be measured accordingly.