Dead Reckoning feature

Introduction

Dead Reckoning is a navigation technique used to estimate current position of vehicle , direction of movement, based on its previous position and known speed. It uses additional sensor data to correct the position received from GNSS receiver.

Usage of Dead Reckoning is essential in scenarios where GNSS signal is weak or unavailable, such as underground parking lots, tunnels or dense forests.

Note: Dead Reckoning is enabled for all FT platform devices with gyroscope. At the moment, it’s not possible to disable it.

Prerequisites

Key points to understand before utilizing the Dead Reckoning functionality:

• Installation
• Configuration
• Alignment

Installation

The device must be mounted firmly in the vehicle, with good visibility of the sky. Failure to ensure proper mounting will result in inability to calibrate the device or inaccurate position estimation. DIN1 should be connected to the vehicle ignition ( applicable to trackers with DIN1), it will be used to detect both ignition status and movement, ensuring optimal performance. Following examples ensure that the GNSS antenna is facing towards the sky and there are no physical obstacles, like metal plates, wires, are blocking the GNSS signal.

Good mounting examples ( If vehicle has a heated windshield, you should look for an alternative mounting location in the trunk, on some sturdy metal closer to backseat window):

Dashboard in the middle of the car mount

Beneath the speedometer panel

Above glove box

Bad mounting examples:

Unwanted movements will be detected by the IMU

Metal parts above the mount

Places, where vibration could cause unwanted device movements

Configuration

The Dead Reckoning feature is configurable via the Dead Reckoning section in the GNSS settings group under System view in TCT.

Parameter list can be found here.

Dead Reckoning alignment status

The Dead Reckoning alignment status is a 1-byte AVL ID (1433) that indicates the current status of the Dead Reckoning alignment. The possible values are:

• 0 - Unknown: Dead Reckoning status is unknown.
• 1 - Init: Dead Reckoning alignment is initializing.
• 2 - Coarse: Dead Reckoning is in alignment stage.
• 3 - Stable: Dead Reckoning alignment stage has been completed. Estimation stage is in progress.
• 99 - Standby: Dead Reckoning is in standby mode (NOTE: this status is availabe with 3.7.X or newer firmware version)

Alignment
Once device mounting adheres to the guidelines, alignment can be performed. The device must finish a specific alignment process to determine its mounting orientation. During this process, there are specific conditions that must be met:

1. The device must be stationary with clear sky visibility for at least 3 minutes.
2. The speed of the vehicle must not be bellow 10 km/h or exceed 50 km/h.
3. Avoid driving in underground tunnels or areas with poor GNSS signal, otherwise alignment needs to be restarted from the second step.

We are currently using only the Swift alignment type. Other types are still unreliable and do not provide better results.

Limitations

There are some important things to keep in mind when using the Dead Reckoning functionality. The algorithm tries to correct for these issues, but sometimes they can still affect how well Dead Reckoning works.

• Position accuracy may decrease - If the device cannot receive a GNSS signal for a long time, the estimated position may become less accurate. This is because the sensors inside the device can only estimate the position for a limited time without help from GNSS.

For example: If a courier spends up to 30 minutes unloading in the underground car park, DR will remain accurate. Otherwise, positioning information will become less accurate.

• Temperature effects - The accuracy of the position can change if the temperature is very different from when the device was last calibrated.
• Alignment reset - If the device loses power or goes into sleep mode, it will need to be calibrated again.

Tip: If alignment auto-save is enabled, realignment will be faster.

• Position jumps after GNSS outages - After the device has been in an area with no GNSS signal for a while (such as near tall buildings or obstacles), you might notice sudden jumps in the position when the signal returns. This happens because the device uses the GNSS signal to correct its estimated position, and the type of GNSS signal used is more sensitive to interference from nearby objects.
• Stand by mode - This feature allows calibration data to be stored for unlimited time, meaning that Dead Reckoning will work accurately even if a week has passed while vehicle was left in underground parking. Functionality will be present in 3.7.X firmware version, so current solution is limited and tracker will lose Dead Reckoning alignment after an hour has passed since ignition OFF event. If vehicle was parked for less than 1 hour, track might be slightly tilted, but if parking lasts more than an hour - GNSS fix needs to be re-acquired. This applies for above and underground parking.

Parameter list

Property ID in AVL packet	Property Name	Bytes	Min Value	Max Value	Multiplier	Units	Description
1433	Dead Reckoning alignment status	1	0	99	1		Dead Reckoning alignment status
1434	Turning alignment	1	0	100	1	%	Turning alignment
1435	Straight alignment	1	0	100	1	%	Straight alignment