Chapter 3 SPAN Operation
OEM7 SPAN Installation and Operation User Manual v14
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option that allows the offsets to be entered relative to the Vehicle Frame. In these cases, the rotation from the
IMU Body Frame to the Vehicle Frame (RBV) is used to rotate offsets into the default IMU Body frame as
required. To achieve the best results, this means that the RBV rotation must be known very precisely. Typically
this is achieved through the SPAN RBV Calibration procedure. See
Body to Vehicle Frame Rotation Calibration
on page 102 or
Multi-Line Body to Vehicle Frame Rotation Calibration Routine
on page 103 for inform-
ation about this calibration procedure.
3.2.2 Rotational Offsets
The differences in orientation between the IMU and other SPAN components are called rotational offsets. Rota-
tional offsets are given as the rotation from the IMU Body Frame to the frame of interest.
The order of rotations is Z-X-Y and all rotations are right handed.
Generally, frames of reference are defined as Z up, with Y forward, and X completing the right-handed system.
An example is the vehicle frame, where Z is always considered to be upwards, Y forward through the direction of
travel, and X to the right.
Rotational Offsets - Example
Consider an IMU installed in the following way:
Here, the Euler Angles to rotate from the IMU Body frame to the Vehicle frame (RBV) are:
l
X: -90
l
Y: 0
l
Z: +90
To reach this answer, keep in mind the following rules:
l
The goal is to rotate the IMU Body frame to be coincident with the Vehicle frame (i.e. IMU X equals Vehicle
X, IMU Y equals Vehicle Y, IMU Z equals Vehicle Z).
l
You must rotate from the IMU Body frame to the Vehicle frame.
l
You must rotate in the order Z, X, Y.
l
Positive rotation is defined according to the right hand rule.
