Chapter 4 SMART7 with SPAN Operation
SMART7 Installation and Operation User Manual v6
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Description
10
WAITING_
AZIMUTH
The INS filter has determined the IMU orientation, received an initial position and
completed initial bias estimates. Azimuth input (from vehicle motion, dual antenna or
command) is required for alignment.
11
INITIALIZING_
BIASES
The INS filter has determined the IMU orientation, received an initial position and is
conducting an initial IMU bias estimate.
12
MOTION_
DETECT
Vehicle motion has been detected during the alignment procedure.
4.5.1 System Start-Up and Alignment Techniques
The system requires an initial position, velocity and attitude estimate to start the navigation filter. This is called
system alignment. On start-up, the system has no position, velocity or attitude information. When the system is
first powered up, the following sequence of events happens:
1. The first satellites are tracked and coarse time is solved.
2. Enough satellites are tracked to compute a position.
3. Receiver “fine time” is solved, meaning the time on board the receiver is accurate enough to begin timing
IMU measurements.
4. The INS Status field changes from INS_INACTIVE through DETERMINING_ORIENTATION and
WAITING_INITIALPOS.
5. Once a GNSS position is available, an initial IMU bias estimate is conducted. During this period, the INS
Status field reports INITIALIZING_BIASES.
6. After the bias estimate is complete, the coarse alignment routing starts. Bias estimates will be refined and a
static alignment completed, if IMU quality allows. During this period the INS Status field reports INS_
ALIGNING.
7. If static coarse alignment is not possible or is locked out by command, the system will require an external
azimuth input, either from vehicle motion, dual antenna input or command input. While in this state the INS
Status field reports WAITING_AZIMUTH.
If vehicle movement is detected, any ongoing static coarse alignment will be reset, and the INS Status field
will report MOTION_DETECT.
8. After an alignment is completed, the INS Status field changes to INS_ALIGNMENT_COMPLETE. The sys-
tem transitions to navigation mode.
9. The solution is refined using updates from GNSS. Once the system is operating within specifications and
after some vehicle movement, the INS Status field changes to INS_SOLUTION_GOOD. This indicates that
the INS filter has successfully converged to within performance specifications.
Kinematic Alignment
The kinematic or moving alignment is performed by estimating the heading from the GNSS velocity vector and
injecting it into the SPAN filter as the initial system heading.
For the kinematic alignment routine to work optimally, the course-over-ground azimuth must not include any bias
from the defined Vehicle Frame. (For example, a plane being blown in the wind has a large ‘crab angle’ and the
course-over ground trajectory will not match the direction the IMU is pointing.)
