Chapter 3 SPAN OperationOEM7 SPAN Installation and Operation User Manual v14 95Binary ASCII Description6INS_SOLUTION_FREEThe INS filter is in navigation mode and the GNSS solution is suspected to be inerror.This may be due to multipath or limited satellite visibility. The inertial filter hasrejected the GNSS position and is waiting for the solution quality to improve.7INS_ALIGNMENT_COMPLETEThe INS filter is in navigation mode, but not enough vehicle dynamics have beenexperienced for the system to be within specifications.8 DETERMINING_ORIENTATION INS is determining the IMU axis aligned with gravity.9 WAITING_INITIALPOSThe INS filter has determined the IMU orientation and is awaiting an initial positionestimate to begin the alignment process.10 WAITING_AZIMUTHThe INS filter has determined the IMU orientation, received an initial position andcompleted initial bias estimates. Azimuth input (from vehicle motion, dual antenna orcommand) is required for alignment.11 INITIALIZING_BIASESThe INS filter has determined the IMU orientation, received an initial position and isconducting an initial IMU bias estimate.12 MOTION_DETECT Vehicle motion has been detected during the alignment procedure.3.4.1 System Start-Up and Alignment TechniquesThe system requires an initial position, velocity and attitude estimate to start the navigation filter. This is calledsystem alignment. On start-up, the system has no position, velocity or attitude information. When the system isfirst 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 timingIMU measurements.4. The INS Status field changes from INS_INACTIVE through DETERMINING_ORIENTATION andWAITING_INITIALPOS.5. Once a GNSS position is available, an initial IMU bias estimate is conducted. During this period, the INSStatus field reports INITIALIZING_BIASES.6. After the bias estimate is complete, the coarse alignment routing starts. Bias estimates will be refined and astatic 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 externalazimuth input, either from vehicle motion, dual antenna input or command input. While in this state the INSStatus field reports WAITING_AZIMUTH.If vehicle movement is detected, any ongoing static coarse alignment will be reset, and the INS Status fieldwill report MOTION_DETECT.8. After an alignment is completed, the INS Status field changes to INS_ALIGNMENT_COMPLETE. The
