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Understanding Position Flags for Third-Party Integration

This article explains how to interpret position flag confidence levels to ensure the most effective integration.

Introduction to Position Flags

Position flags are generated by ZeroKey’s RTLS by assigning a confidence level to each Mobile’s position. Understanding these flags is essential for building a reliable integration. Filtering for the right position flag ensures that only the most accurate Mobile positions are incorporated into your data.

ZeroKey’s RTLS 2.0 platform employs two categories of position flags, each segmented into confidence levels. It’s important to consider both categories when building your integration.

Ultrasonic (US) Position Flags

ZeroKey’s positioning accuracy relies on ultrasonic pulses emitted by the Mobile, detected by Anchors within a set range. ZeroKey assigns a confidence level to the Mobile’s position based on how many Anchors detect the ultrasonic pulse. The more Anchors that detect the pulse, the higher the system’s confidence in the reported Mobile’s position.

Ultrasonic Flag Value

Description

Flag 3

Successful position with the highest confidence level. This flag utilizes 4 or more Mobile to Anchor Ranges.

Flag 2

Successful position with reduced confidence. This flag utilizes 1 to 3 Mobile to Anchor Ranges.

Flag 1

This flag resorts to using a dead-reckoned position based on the Mobile’s existing trajectory.

Flag 0

This flag is generated when no Mobile to Anchor Ranges are available.

Although using position flag 3 for your integration is strongly advised for its high degree of certainty by the system, it can be beneficial to also include position flags 1 or 2. These flags could provide valuable data for maintaining an approximation of the Mobile’s position.

Inertial Navigation System (INS) Position Flags

ZeroKey’s RTLS system can be set up to utilize an inertial sensor on each Mobile. By combining inertial data with ultrasonic data, fused positions are produced, providing a wider range of positioning data during active positioning.

While ultrasonic positions are still reported without any alteration to the US position flags, a new category of flags called INS position flags is generated. These flags are solely based on inertial data reported by each Mobile.

INS Flag Value

Description

Flag 4

Indicates that fused positioning is successful. Mobile heading is valid.

Flag 3

Indicates that fused position is valid, however Mobile heading is still converging.

Flag 2

Only INS positions are available due to a loss of ultrasonic positions.

Flag 1

Indicates INS instability and position uncertainty.

Flag 0

INS is not enabled (ultrasonic mode only).

Sample Log

The following log excerpt shows US and INS flags in the last line of text, noted as pf: 43. The first digit indicates the US flag and the second digit indicates the INS flag.

[2024-02-07T12:43:04.3267] COM10: |I| rf_cmd_update_position: Node:
FE:D6:75:67:D7:49 seq: 4360 ins: 3 pos: 11.35546,3.18311,1.99053 vel:
0.01978,0.00743,0.00019 rot: 0.86897,0.07986,0.03816,0.48688 flag: 00
pf: 43 ts: 7801033839

In the device log, the INS position flag is reported first, followed by the US position flag. In the example provided, the highest quality positions are reported in both categories.

To customize the filtering for the US and INS flags that align with your integration requirements, explore ZeroKey’s API documentation available at https://api.zerokey.com/v3/ .

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