Novatel OM-20000122 user manual Default Kinematic Alignment, Setimuorientation

Chapter 3 SPAN-CPT Operation

7.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 estimated azimuth standard deviation is below 2 degrees. If it increases above 2 degrees, the status changes to INS_HIGH_VARIANCE.

The azimuth standard deviation threshold can be changed using the INSTHRESHOLDS command. See the SPAN on OEM6 Firmware Reference Manual (OM-20000144) for information about this command.

3.4.1.1Default Kinematic Alignment

A kinematic alignment is the default alignment routine for SPAN-CPT.

If the system is mounted as recommended with the z-axis pointing up and the y-axis aligned with the forward direction of the vehicle, then no additional configuration is required to complete a moving alignment.

The kinematic alignment begins when the receiver has a good GNSS position, fine time is solved, the configuration parameters have been set and a GNSS velocity of at least 5 m/s (~ 18 km/h) is observed. During kinematic alignment, keep the vehicle roll at less then 10°. Straight line driving is best.

5 m/s is the default alignment velocity. If a different alignment velocity is required, it can be changed using the SETALIGNMENTVEL command. See the SPAN on OEM6 Firmware Reference Manual (OM-20000144) for more information.

The moving alignment transfers the GNSS course over ground pitch and azimuth to the attitude of the IMU. This alignment routine is best suited for ground vehicles where the direction of travel is coincident with the forward axis of the vehicle and the roll of the vehicle is close to zero. The fast alignment routine may not be suitable for some marine or airborne applications, where the direction of travel may be different from the forward axis of the vehicle because of factors like a crab angle.

If SPAN-CPT is installed with the IMU axes NOT aligned with the vehicle, then additional configuration is needed to complete the moving alignment. These settings can be set graphically using the INS configuration wizard in the NovAtel Connect utility or through the command interface by issuing the following commands:

1.Specify which IMU axis is most closely aligned with gravity using the SETIMUORIENTATION com- mand. See the SPAN on OEM6 Firmware Reference Manual (OM-20000144) for a description of this command and Table 3, Full Mapping Definitions on page 21 for the number corresponding to each orientation. For example, if the z-axis of the SPAN-CPT is pointing up, send this command:

SETIMUORIENTATION 5

2.Specify the angular offset from the vehicle frame to the SPAN frame (known as the vehicle/body rotation or RVB) using the VEHICLEBODYROTATION command. Details of this command are in the SPAN on OEM6 Firmware Reference Manual (OM-20000144).

Following the example started above, if the SPAN-CPT is installed rotated so that the y-axis points out the right side of the vehicle instead of forward, enter this command:

VEHICLEBODYROTATION 0 0 -90

axis that +Z pointing up, use the NovAtel Connect SPAN wizard for assistance with these settings.Angular rotations are difficult to visualize, so if you have complex rotations or some other

The accuracy of the initial attitude depends on the dynamics of the vehicle and the accuracy of the angles input in the VEHICLEBODYROTATION command. The alignment is only an estimate of the attitude of the vehicle and as the vehicle experiences dynamics, the accuracy of the attitude solution improves. Once the attitude accuracy has converged the INS status changes to “INS_SOLUTION_GOOD”.

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