ZED-F9R-Integration manual
• IMU-mount roll/pitch angle initialization ongoing: The alignment engine is initializing the IMU-
mount roll and pitch angles (UBX-ESF-ALG.status is 1). Both angles can only be initialized if
vehicle encounters left and right turns (as during a normal drive).
• IMU-mount yaw angle initialization ongoing: The alignment engine is initializing the IMU-
mount yaw angle (UBX-ESF-ALG.status is 2). IMU-mount yaw angle can only be initialized
once IMU-mount roll and pitch angles are initialized and if vehicle encounters left and right
turns (as during a normal drive).
•
IMU-mount alignment coarse calibration ongoing: Once initialized (UBX-ESF-ALG.status
is 3), the automatic IMU-mount alignment engine has sufficient confidence in all IMU-
mount misalignment angles and validates their use for compensating the accelerometer and
gyroscope data (fused navigation solutions can be computed). The IMU-mount misalignment
angles are filtered each time the observed vehicle dynamics are measurable.
• IMU-mount alignment fine calibration ongoing: Once the IMU-mount misalignment angles are
estimated with a good accuracy, the automatic IMU-mount alignment engine becomes more
conservative in updating the IMU-mount misalignment angles (UBX-ESF-ALG.status is 4).
3.2.7.3.3 Alignment reset
If for some reasons the IMU-mount misalignment angles estimated by the automatic IMU-mount
alignment engine are no longer valid (for example due to a change in the physical mounting of
the device), the IMU-mount misalignment angles can be reset by sending a UBX-ESF-RESETALG
message. In addition, the misalignment angles are also reset in the following cases:
• If a cold start command is sent.
• If the user-defined IMU-mount misalignment angles are changed by sending CFG-SFIMU-
IMU_MNTALG keys (see User-defined IMU-mount alignment section for more details.
The IMU-mount alignment engine then falls back into initialization mode.
3.2.7.3.4 Alignment errors
The following errors might be output in the UBX-ESF-ALG.error bit field:
• IMU-mount roll/pitch angle error: If the automatic IMU-mount alignment engine suspects
wrong IMU-mount roll and/or IMU-mount pitch misalignment angles (either due to a wrong
initialization or a change in the physical mounting of the device), the UBX-ESF-ALG.error bit
0 is set to 1.
• IMU-mount yaw angle error: If the automatic IMU-mount alignment engine suspects wrong
IMU-mount yaw misalignment angle (either due to a wrong initialization or a change in the
physical mounting of the device), the UBX-ESF-ALG.error bit 1 is set to 1.
•
Euler angle singularity ('gimbal-lock') error: The Euler angle singularity UBX-ESF-ALG.error
bit 2 is set when the automatic IMU-mount alignment engine detects an installation where the
IMU frame is misaligned in such a way that a degree of freedom is lost when two IMU-mount
misalignment (Euler) angles begin to describe the same rotations (or axes). This happens, for
example, with an IMU-mount misalignment of +/- 90 degrees around the IMU-mount pitch
axis, where IMU-mount roll and IMU-mount yaw cannot be distinguished from each other.
In such a case, these IMU-mount misalignment angles start to heavily fluctuate with time
due to the mathematical singularity occurring at these points, meaning that the IMU-mount
misalignment angles output in the UBX-ESF-ALG are not stable in time. Note however that
each individual set of IMU-mount misalignment angles output in such a case still describes the
correct rotation. Moreover, the internal rotation applied for aligning the IMU readings does not
suffer from this singularity issue and optimal fusion can still be achieved.
3.2.7.4 Navigation output
3.2.7.4.1 Local-level north-east-down (NED) frame
The local-level frame is a geodetic frame with the following features:
UBX-20039643 - R06
3 Receiver functionality Page 35 of 119
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