Filter Initialisation

After all four levels of initialisation, the Certus INS filter takes several minutes to achieve its full accuracy. It is recommended to wait two minutes after initialisation for applications requiring high accuracy.

Orientation Initialisation

Orientation initialisation occurs automatically upon power on and typically completes within seconds. To determine its orientation it uses the accelerometers to measure the gravity vector. Random accelerations from environmental sources can disturb this process, which can introduce minor orientation errors that will be corrected within several seconds. To prevent this, Certus monitors the accelerometers and gyroscopes and restarts the orientation detection if there are sudden movements. It is however still possible under some circumstances for it to miss minor movements and start with a small orientation error. Certus will progressively correct the orientation error over a period of several seconds.

Once orientation initialisation is complete, the roll, pitch and angular velocity values will be valid.

Navigation Initialisation

Navigation initialisation completes once the system has determined a starting absolute position. The most common method of navigation initialisation is for the system to get a 3D GNSS fix or better. If the system is hot-starting it will remember its position at the time it was switched off and use this as the starting position. The other possibility for navigation initialisation is an external position source to be used, see External Position Packet for more information. In a situation where a GNSS fix is not available to initialise navigation, it can be initialised manually by entering a position into the Manual Initialisation page in the web UI or the Manual Initialisation dialogue in the Certus Manager.

Once navigation initialisation is complete, the position, velocity and acceleration values will be valid.

Heading Initialisation

Heading initialisation completes once the system has determined a heading using one of its several methods. The conditions required to determine a heading depend upon the heading source being used, see Heading Sources. The default heading source is dual antenna, which will initialise the heading to a high accuracy within several minutes of power on assuming that both antennas are connected with an unobstructed view of the sky. The system can be stationary or moving during this initialisation. If velocity heading is enabled and the vehicle is moving, this will be very fast. If the system hot-starts, the last known heading value will be used. However, in order for the Heading Filter to initialise, the system must have a valid heading source.

Until the heading has been initialised, the system will not be able to navigate without a GNSS fix, and the roll and pitch values will not reach full accuracy.

Time Initialisation

Time initialisation completes once the system has determined time accurately. This occurs as soon as the GNSS receiver obtains its first fix. For this to occur the system must receive rough time as well as a 1PPS signal on one of the GPIO pins. It is also possible to acquire time from an external source, see External Time Packet for more information.

Until the time has initialised, the Unix or formatted time that Certus outputs will be flagged as invalid.