Novatel SPAN-SE User Manual Download

Page: 45 / 300

SPAN-SE Operation

Chapter 3

SPAN-SE User Manual Rev 1

tions and after some vehicle movement, the INS Status field changes to

INS_SOLUTION_GOOD. This indicates that the estimated azimuth standard deviation is below



. If it increases above 2



the status changes to

INS_SOLUTION_NOTGOOD.

3.4.3.1

Coarse Alignment

The coarse alignment is the default alignment routine for SPAN. The alignment starts as soon as a

GNSS solution is available, the receiver has computed fine time and the IMU is connected and

configured. The vehicle must remain stationary for the alignment to happen. During the coarse

alignment, accelerometer and gyro measurements are averaged over a period of time to measure Earth

rotation and gravity. From these averaged measurements, initial estimates of roll, pitch and heading

are computed. Because the coarse alignment uses averaged sensor output, the vehicle must remain

stationary for the duration of the alignment, which is approximately 1 minute. The attitude estimates

solved by the alignment are larger than the system specified attitude accuracy and vary upon the

characteristics of the sensor and the geographic latitude of the system. Attitude accuracy converges

with motion after the coarse alignment is complete (see

Section 3.4.4, Navigation Mode

Page 46

If the system is stationary for less than 1 minute, the coarse alignment finishes early, provided at least

5 stationary seconds were detected. The quality of the coarse alignment is poorer with stationary

durations of less than 1 minute.

3.4.3.2

Kinematic Alignment

If the preferred coarse alignment routine cannot be performed because the vehicle cannot remain

stationary for the length of time required, an alternate alignment routine is available. The kinematic or

moving alignment is performed by estimating the attitude from the GNSS velocity vector and

injecting it into the SPAN filter as the initial system attitude.
Currently, this alignment routine is meant only for ground-based vehicles. The assumptions used for

the alignment may not hold for marine or airborne applications. For the fast alignment routine to work

optimally, the course-over-ground’s azimuth and pitch must match the SPAN computation frame’s

azimuth and pitch. (For example, a plane being blown in the wind has a a large ‘crab angle’ and the

course-over ground trajectory will not match the direction the IMU is pointing.)
Additional configuration parameters are necessary to enable the kinematic alignment. In order to

simplify this configuration it is strongly suggested that you mount the IMU in parallel to the vehicle

frame. The Y axis marked on the IMU enclosure, should point in the direction of travel.
Specify which IMU axes are most closely aligned with gravity using the SETIMUORIENTATION

command. If the IMU is mounted with the Z-axis up and the Y-axis pointing in the direction of travel,

then the command would be:

SETIMUORIENTATION 5

Specify the angular offsets between the SPAN frame and the vehicle frame (known as vehicle/body

rotation or RVB) using the VEHICLEBODYROTATION command, see

Page 148

. If the IMU is

mounted coincidentally with the vehicle frame (defined as z up and y pointing in the direction of

travel), then the command would be:

VEHICLEBODYROTATION 0 0 0

Alternatively, solve the vehicle to IMU frame angular offsets using the RVBCALIBRATE routine. See

also