INS Seed / Fast INS initialization

Platform: 

OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, CPT7, CPT7700, SMART7-S

The INS Seed functionality is an alignment method whereby INS alignment information from a previous power up can be injected into the system at start up to achieve an INS alignment more quickly. This is especially useful for systems that previously required a kinematic alignment.

When INS Seed is enabled, alignment data is automatically saved when appropriate, with no specific action required from the user. During subsequent power ups, the saved solution is compared to the current azimuth of the system, and if valid, the saved solution is used to immediately align the inertial filter, making it ready for use.

Error model information is also saved with the seed data. Even if full alignment cannot be achieved, this information can still be used to aid filter convergence, although another method of alignment will be required.

This feature is enabled via the INSSEED command. This command setting must be saved to NVM via the SAVECONFIG command to be used upon next system boot-up.

Criteria

For the INS seed functionality to be enabled, the INSSEED ENABLE command must be sent.

Saving

The following criteria must be met for valid alignment data to be saved into receiver NVM.

  • The INS solution status must be converged, as indicated by the INS solution convergence flag in the inertial Extended Solution Status (see Table: Extended solution status).

  • The system is stationary.

When these conditions are met, the required information is automatically saved to NVM. If these conditions cease to be met, the saved alignment data is automatically discarded. If the alignment data is discarded, error model information is automatically retained as appropriate.

Use at boot-up

Upon boot, checks are done to verify that any seed data existing in NVM is appropriate for use. These checks require a GNSS position to be computed, so an NVM seed will never use the INJECTED status prior to achieving a GNSS position. The following criteria must be met in order to use a seed:

  • Seed data from NVM must be valid

  • The system must not have changed more than 10 degrees in heading

If the INJECT Error Model Option is selected, and a valid error model is present in the seed data from NVM, this will always be used, even if the system has exceeded attitude validation thresholds. This functionality may be disabled with the IGNORE Error Model Option

INJECT Option (Advanced Users Only)

There is an advanced option available to skip the second and third validation steps described in the boot-up section above. This can be used if GNSS is not available on power-up or if speed to achieve an alignment is imperative.

This option is for advanced users only. Forcing an injection of an NVM seed without the validation checks can cause an unstable INS solution if the vehicle has moved.

Apart from injecting the seed at start-up without validation, this will also remove some requirements typically asserted to allow the filter to converge. This will allow the system to run without GNSS adequately at start-up.

Example usage

Enabling functionality after FRESET:

  1. Send the following command.

    INSSEED ENABLE VALIDATE INJECT

  2. Send the following command.

    SAVECONFIG

Saving valid INS information:

  1. Operate the system as normal, until the filter completes convergence.

  2. Bring the system to a complete stop before powering off or resetting.

Using valid INS information on start-up:

  1. Remain static while initializing.

  2. Wait for the system to receive a valid position from GNSS.

  3. If using ALIGN updates, INS Seed data will be validated and injected. If not, drive forward to validate and inject the INS Seed.

System indicators

The INSSEEDSTATUS log reports the seed injection status for the current power up and information on current seed validity.

The Extended Solution Status field in the INSPVAX log has bits that indicate if the alignment direction is verified, the Alignment type that occurred and NVM seed injection status.

Alignment direction verified: Bit 25

This bit indicates whether the alignment is verified or not. When the seed is injected and kinematic validation is finished, bit 25 is set to 1. Note that this bit will not be set until the kinematic validation completes. When the INJECT option is used, validation is skipped and this bit will not be set.

Alignment type: Bits 26-28

These bits indicate how the INS system reached INS_ALIGNMENT_COMPLETE. When the INS system aligns using saved INS solution data from NVM, bits 26-28 will be set to 101

NVM seed status: Bits 29-31

These bits indicate the current status of the seeding process at start-up, as described in the table below:

NVM seed indication

Bit 31-29
values1

Hex value

NVM seed type

001

0x01

INS Seed in non-volatile memory is invalid

010

0x02

INS Seed has failed validation and has been discarded

011

0x03

INS Seed is pending validation

100

0x04

INS Seed alignment data has successfully been injected