IMU mount alignment

This page documents the IMU mount alignment configuration.

The physical mounting orientation of the CANmod.gps may not align with the orientation of the application in which it is installed. The IMU mount alignment configuration can be used to virtually rotate the device such that it becomes aligned with the application. Aligning the IMU and the application makes it easier to interpret the IMU output.

Warning

IMU mount alignment is required if the automotive sensor fusion feature is enabled. The sensor fusion model assumes that the output of the IMU is aligned with the automotive installation coordinate system. The sensor fusion result can be degraded if the IMU is misaligned a few degrees and can fail completely if the misalignment reaches tens of degrees.

Configuration file fields

This section is autogenerated from the Rule Schema file.

IMU-mount alignment sensor.imu_mount_alignment

IMU-mount alignment configuration

Z angle (0, 360) sensor.imu_mount_alignment.z

Type	Default	Minimum	Maximum
integer	0	0	360

Y angle (-90, 90) sensor.imu_mount_alignment.y

Type	Default	Minimum	Maximum
integer	0	-90	90

X angle (-180, 180) sensor.imu_mount_alignment.x

Type	Default	Minimum	Maximum
integer	0	-180	180

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Configuration explained

This section contains additional information and examples.

If the device is installed such that the IMU-coordinate system and the installation-coordinate system have the same orientation, then the alignment angles can all be set to zero (default).

The Z, Y and X alignment angles represent the Euler-angles required to rotate the installation-coordinate system to the IMU-coordinate system. If multiple angles are misaligned, then the Z rotation should be performed first, then the Y rotation and finally the X rotation.

Warning

It is recommended to install the device such that no more than a single angle is misaligned. Configuring multiple misaligned angles is difficult.

It is generally up to the user to define the installation frame (how the application is oriented). However, if sensor fusion is used then the device assumes a specific automotive installation frame as described in the Automotive sensor fusion Section.

Example, Z misalignment

The required misalignment angle is determined by imagining that the installation-coordinate system is rotated such that it becomes oriented as the IMU-coordinate system.

Below Figure illustrates how the installation-coordinate system is rotated by -30° to align with the IMU-coordinate system.

As defined in the Configuration file fields above, the valid range of the Z angle specifically is 0-360°. To configure a Z misalignment angle of -30°, we calculate the equivalent angle to 360-30 = 330°.

The misalignment configuration becomes:

"imu_mount_alignment": {
    "z": 330,
    "y": 0,
    "x": 0
}