Methods and apparatus for providing a snapshot truthing system for a tracker

• US 9,489,045 B2
• Filed: 03/26/2015
• Issued: 11/08/2016
• Est. Priority Date: 03/26/2015
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Larson, Brent D., Leiphon, Ken
• Primary Examiner(s): Li, Lin
• Application Number:
  US14/669,336
• Publication Number:
  US 20160282936A1
• Time in Patent Office: 593 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2034/2048 using an accelerometer or inertia sensor
• CPC Class Codes: A61B 2090/0818 Redundant systems, e.g. using two independent measuring systems and comparing the signals
• CPC Class Codes: A61B 34/20 Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis
• CPC Class Codes: A61B 5/1114 Tracking parts of the body
• CPC Class Codes: A61B 5/6803 Head-worn items, e.g. helmets, masks, headphones or goggles
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: G01C 23/00 Combined instruments indicating more than one navigational value, e.g. for aircraft; Combined measuring devices for measuring two or more variables of movement, e.g. distance, speed or acceleration
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 5/163 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49
• CPC Class Codes: G01S 5/18 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G02B 2027/014 comprising information/image processing systems
• CPC Class Codes: G02B 2027/0187 slaved to motion of at least a part of the body of the user, e.g. head, eye
• CPC Class Codes: G02B 27/017 Head mounted
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 27/0179 Display position adjusting means not related to the information to be displayed
• CPC Class Codes: G06F 3/011 Arrangements for interaction with the human body, e.g. for user immersion in virtual reality blind teaching G09B21/00
• CPC Class Codes: G06F 3/012 Head tracking input arrangements
• CPC Class Codes: G06F 3/017 Gesture based interaction, e.g. based on a set of recognized hand gestures interaction based on gestures traced on a digitiser G06F3/04883

Abstract

A method for detecting and correcting drift associated with operation of a hybrid tracking system is provided. The method obtains a data signal from a first tracker subsystem having a first tracker latency time; for a defined window of time, the method captures snapshot input data for a second tracker subsystem having a second tracker latency time which is longer than the first tracker latency time; and captures synchronized data from the data signal which corresponds to the defined window of time; wherein the defined window of time comprises a time duration shorter than the second tracker latency time, to capture the snapshot input data. The method further determines a level of drift associated with operation of the first tracker subsystem; and adjusts operation of the first tracker subsystem according to the determined level of drift.

Claims

1. A method for detecting and correcting drift associated with operation of a hybrid tracking system, the method comprising:

obtaining a data signal from a first tracker subsystem having a first tracker latency time;

for a defined window of time,

capturing snapshot input data for a second tracker subsystem having a second tracker latency time which is longer than the first tracker latency time; and

capturing synchronized data from the data signal which corresponds to the defined window of time;

wherein the defined window of time comprises a time duration shorter than the second tracker latency time, to capture the snapshot input data;

calculating second tracker snapshot results from the captured snapshot input data for the second tracker subsystem;

calculating first tracker snapshot results from the captured synchronized data from the first tracker subsystem;

calculating an error between the first tracker snapshot results and the second tracker snapshot results, to determine a level of drift associated with operation of the first tracker subsystem; and

adjusting operation of the first tracker subsystem according to the determined level of drift.

2. The method of claim 1, wherein the first tracker snapshot results comprise an inertial estimate of position, relative to a reference frame, from the first tracker subsystem;

and

wherein the second tracker snapshot results comprise a non-inertial estimate of position from the second tracker subsystem.

3. The method of claim 1, wherein the adjusting step further comprises adding a translational offset to an output signal, and wherein the translational offset comprises the calculated error,

wherein the data signal comprising the output signal.

4. The method of claim 1, wherein the adjusting step further comprises performing a rotational computation using an output signal, and wherein the rotational computation comprises the calculated error,

wherein the data signal comprising the output signal.

5. The method of claim 1, further comprising:

determining whether the calculated error comprises a result consistent with a previously calculated error; and

performing the adjusting step when the calculated error and the previously calculated error comprise consistent values.

6. The method of claim 1, further comprising:

determining whether the calculated error comprises a result consistent with a plurality of previously calculated errors; and

performing the adjusting step when the calculated error and the previously calculated errors comprise consistent values.

7. The method of claim 1, wherein the second tracker latency time comprises a duration of time greater than ten times longer than the first tracker latency time.

8. The method of claim 1, further comprising:

calculating a weighted average of the calculated error and a plurality of previously calculated errors; and

determining the level of drift based on the calculated weighted average.

9. A head-worn display apparatus, configured to provide a conformal near-to-eye (NTE) display, the apparatus comprising:

a hybrid tracking system, comprising;

an inertial tracker, configured to provide first positional data of the head-worn display apparatus, with regard to an inertial reference frame;

a non-inertial tracker, configured to provide second positional data of the head-worn display apparatus, with regard to the inertial reference frame;

a snapshot module, configured to;

determine a snapshot time frame by coordinating a window of time for gathering input data for the non-inertial tracker;

synchronize operation of the inertial tracker and the non-inertial tracker; and

capture a relevant subset of the first positional data associated with the determined snapshot time frame and a relevant subset of the second positional data associated with the determined snapshot time frame;

a drift detection module, configured to compare the relevant subset of first positional data with the relevant subset of second positional data, to determine an offset; and

a drift correction module, configured to adjust operation of the inertial tracker, based on the determined offset.

10. The system of claim 9, wherein synchronizing operation of the inertial tracker and the non-inertial tracker further comprises synchronizing a data signal of the inertial tracker with an input signal of the non-inertial tracker.

11. The system of claim 9, wherein the non-inertial tracker comprises an optical tracker.

12. The system of claim 9, wherein the non-inertial tracker comprises a magnetic tracker.

13. The system of claim 9, wherein the determined offset comprises error associated with one or more orientational degrees of freedom (DOF);

and

wherein the adjustment of the operation of the inertial tracker comprises performing a rotational computation to accommodate the error associated with one or more DOF.

14. The system of claim 9, wherein the determined offset comprises a translational error;

and

wherein the adjustment of the operation of the inertial tracker comprises adding the offset to the first positional data to accommodate the translational error.

15. A non-transitory, computer-readable medium containing instructions thereon, which, when executed by a processor, perform a method comprising:

synchronizing an inertial tracker and a non-inertial tracker;

identifying a snapshot time-frame, based on the synchronization step;

during the snapshot time-frame, obtaining input data for the non-inertial tracker;

obtaining data from the inertial tracker corresponding to the snapshot time-frame;

obtaining a first result from the inertial tracker and a second result from the non-inertial tracker, each representative of the snapshot time-frame;

comparing the first result to the second result to obtain a discrepancy result; and

modifying operation of the inertial tracker, based on the discrepancy result.

16. The non-transitory, computer-readable medium of claim 15, wherein the synchronizing step further comprises synchronizing an output signal of the inertial tracker to an input signal of the non-inertial tracker;

and

wherein the first result comprises the output signal.

17. The non-transitory, computer-readable medium of claim 15, wherein the identifying step further comprises coordinating the snapshot time-frame based upon the latency time associated with the non-inertial tracker, detected drift rates, and desired measurement accuracies.

18. The non-transitory, computer-readable medium of claim 15, wherein the comparing step further comprises calculating a difference between the first result and the second result for each of a plurality of degrees of freedom (DOF), and wherein the discrepancy result comprises the calculated difference for each of the DOF.

19. The non-transitory, computer-readable medium of claim 15, wherein the discrepancy result comprises a drift offset value;

and

wherein the modifying step further comprises adding the drift offset value to the first result to generate a corrected output signal from the inertial tracker.

20. The non-transitory, computer-readable medium of claim 15, wherein the discrepancy result comprises a drift offset value;

and

wherein the modifying step further comprises performing a rotational computation using the drift offset value, to generate a corrected output signal from the inertial tracker.