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Chapter 4 SMART7 with SPAN Operation
SMART7 Installation and Operation User Manual v6
66
Z Rotation
:
Since the Y axis of the IMU Body frame is collinear with vehicle Y axis, a Z rotation is not required.
X Rotation
:
Since the Y axis of the IMU Body frame is collinear with the vehicle Y axis, an X rotation is also not required
Y Rotation
:
Observe that if a 180 degree rotation is performed about the IMU Body frame Y axis, the rotated IMU Z axis is
now collinear with the Vehicle Z axis, and the rotated IMU X axis is also collinear with the Vehicle X axis.
This solution is not unique. Due to the properties of Euler Angles, there are usually multiple sets of equi-
valent rotations.
The rotational offsets are entered using the
SETINSROTATION
command. For this example, the command to
enter the rotations for the previous example is:
SETINSROTATION RBV 0 180 0
4.3.3 Importance of RBV Calibration
For the SMART7 to provide the best performance, the rotation offset of the IMU body to the Vehicle frame (RBV)
should be known as accurately as possible. Since constraints happen at the vehicle level, any error in the offset
will translate into worse performance.
If the SMART7 is installed as described in
Mounting and Orienting the SMART7
on page 26, the IMU Body frame
is aligned with the Vehicle frame. However, aspects of the vehicle design, such as roof camber or tilt, and slight
misalignments in installation can cause the IMU Body frame to be slightly out of alignment with the Vehicle
frame. The misalignment of the IMU Body frame from the Vehicle frame will add a bias to the SPAN solution.
The following diagrams show a SMART7 on the roof of a vehicle with the three issues mentioned above.