NavShoe™ Pedestrian Inertial Navigation Technology Brief

Eric FoxlinAug. 8, 2006

WPI Workshop onPrecision Indoor Personnel Location and

Tracking for Emergency Responders

NavShoe™ Pedestrian Inertial Navigation Technology Brief

Eric FoxlinAug. 8, 2006

WPI Workshop onPrecision Indoor Personnel Location and

Tracking for Emergency Responders

The ProblemThe Problem

• GPS doesn’t work indoors

• Cannot assume a prepared environment or use of any tracking infrastructure

• To obtain meter-level accuracy and thorough coverage with RF/UWB requires setting up multiple antennas around the building

• Pedometer/compass dead-reckoning modules not sufficiently robust and accurate

– Must calibrate for individual user’s step size

– Changes in size of steps cause errors

– Variations in direction of steps cause errors

– Current products specify drift accumulation of 2-5% of distance travelled, and that assumes normal walking with consistent gait.

• GPS doesn’t work indoors

• Cannot assume a prepared environment or use of any tracking infrastructure

• To obtain meter-level accuracy and thorough coverage with RF/UWB requires setting up multiple antennas around the building

• Pedometer/compass dead-reckoning modules not sufficiently robust and accurate

– Must calibrate for individual user’s step size

– Changes in size of steps cause errors

– Variations in direction of steps cause errors

– Current products specify drift accumulation of 2-5% of distance travelled, and that assumes normal walking with consistent gait.

Inertial Navigation –gimbaled stable platform

motor

accelerometersgyros

motor motor

Inertial Navigation -strapdown

-g position

integrationrate

gyros orientation

accelscoord.

transform

ω

double

integration

f

B

fN

gyrosac

cels

position

orientation

BaN

Inertial Navigation –error growth

Inertial Navigation –error growth

100

101

102

103

0

50

100

150

200

250

300

350

400

450

500

seconds

mm

commercial-gradetactical-grade

navigation-grade

strategic-grade

geophysical limit

NavShoe ConceptNavShoe Concept

• Foot-mounted sensor package contains MEMs gyros, accelerometers and magnetometers

• Short-term inertial navigation measures the 6-DOF trajectory of each step – works with any kind of motion

• Break cubic error growth by resetting velocity to zero after each step:

• Take advantage of correlated position/velocity errors in Kalman filter to also remove most position error with each ZVU:

• Correct heading drift of small MEMS gyros, based on compass measurements averaged over a long distance

• Foot-mounted sensor package contains MEMs gyros, accelerometers and magnetometers

• Short-term inertial navigation measures the 6-DOF trajectory of each step – works with any kind of motion

• Break cubic error growth by resetting velocity to zero after each step:

• Take advantage of correlated position/velocity errors in Kalman filter to also remove most position error with each ZVU:

• Correct heading drift of small MEMS gyros, based on compass measurements averaged over a long distance

NavShoe HardwareNavShoe Hardware

Wireless InertiaCube3

foot-mounted sensor

cluster

PDA or wearable computer

GPS

receiv

RF

rcvr

NavShoe data fusion

software

User interface &

information display app

Results (Indoors)Results (Indoors)

• User walked through a typical wood-frame house for 322 seconds, covering a total distance of 118.5 meters.

• Started at position (0,0,0) on the first floor in the living room.

• The final reported x,y,z position of the tracker in meters is (-0.32 0.10 -0.06), indicating that over the whole journey it has drifted by 0.3% of the distance traveled.

• The NavShoe keeps track of the height

• The total drift in altitude over the experiment was only 6 cm, or 0.06% of distance traveled

• User walked through a typical wood-frame house for 322 seconds, covering a total distance of 118.5 meters.

• Started at position (0,0,0) on the first floor in the living room.

• The final reported x,y,z position of the tracker in meters is (-0.32 0.10 -0.06), indicating that over the whole journey it has drifted by 0.3% of the distance traveled.

• The NavShoe keeps track of the height

• The total drift in altitude over the experiment was only 6 cm, or 0.06% of distance traveled

Results (Indoors)Results (Indoors)

easting (meters)-4 -3 -2 -1 0 1 2 3 4 5 6

-2

-1

0

1

2

3

4

5

6

northing (meters)

sofa

dining table

kitchen

1st-floor bedroom

upstairs

bedroombed

Trajectory of NavShoe during 118.5 m exploratory path through house.

Plan view Elevation

-2 -1 0 1 2 3 4

-1

0

1

2

3

4

easting (meters)

up (meters)

Results (Outdoors)Results (Outdoors)Trajectory of NavShoe during 741m road loop.

-50 0 50 100 150

-160

-140

-120

-100

-80

-60

-40

-20

0

20

easting (meters)

northing (meters)

Algorithm for Integration with GPS or LPS

Algorithm for Integration with GPS or LPS

• Initially, inertial heading and magnetic declination both set with high covariances

• As the user walks, heading and declination become highly correlated.

• When GPS becomes available, we use Transfer Alignment measurements after each step to align inertial heading very precisely to true geodetic North.

• Because of the high correlation, this allows the filter to make a precise estimate of magnetic declination.

• During GPS outages, the compass is compensated with declination, and used to keep the inertial heading aligned to geodetic North.

• Long-term navigation fusing GPS with NavShoe could produce results more accurate than GPS alone

• Initially, inertial heading and magnetic declination both set with high covariances

• As the user walks, heading and declination become highly correlated.

• When GPS becomes available, we use Transfer Alignment measurements after each step to align inertial heading very precisely to true geodetic North.

• Because of the high correlation, this allows the filter to make a precise estimate of magnetic declination.

• During GPS outages, the compass is compensated with declination, and used to keep the inertial heading aligned to geodetic North.

• Long-term navigation fusing GPS with NavShoe could produce results more accurate than GPS alone

NavShoe Results w/ GPS Outage (Outdoors)

NavShoe Results w/ GPS Outage (Outdoors)

• User walked a 1059 m closed loop through a very hilly residential neighborhood logging data from the NavShoeand GPS.

• During the first 400m, the GPS fixes were incorporated into the NavShoe Kalman filter

• For the remaining 659 meters, the GPS fixes were completely ignored.

• Data post-processed in Matlab.

• User walked a 1059 m closed loop through a very hilly residential neighborhood logging data from the NavShoeand GPS.

• During the first 400m, the GPS fixes were incorporated into the NavShoe Kalman filter

• For the remaining 659 meters, the GPS fixes were completely ignored.

• Data post-processed in Matlab.

NavShoe w/ simulated Denied GPS (Outdoors)

NavShoe w/ simulated Denied GPS (Outdoors)

-150 -100 -50 0 50 100 150

0

50

100

150

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easting (meters)

northing (meters)

NavShoe

unused GPS fixes

GPS fixes used

for training declination

NavShoe vs. Torso Dead ReckoningNavShoe vs. Torso Dead Reckoning

0.3% of distance walked

2-5% of distance walked

Typical accuracy

NoYesDepends on specific orientation on user’s body

NoYesCan be fooled by non-standard motions

NoYesRequires special algorithms to identify backwards steps

NoYesRequires user calibration/training

NavShoeTorso Dead Reckoning Devices

NavShoe Issues & LimitationsNavShoe Issues & Limitations

• Will users accept shoe-mounted sensor ?

– Maybe as part of

a self-powered insole

• Will the performance hold up for crawling, running and any other maneuvers that firefighters may make?

• Will performance hold up in real-world temperature extremes?

• Will drift be low enough to use it without external position fixes?

• Will users accept shoe-mounted sensor ?

– Maybe as part of

a self-powered insole

• Will the performance hold up for crawling, running and any other maneuvers that firefighters may make?

• Will performance hold up in real-world temperature extremes?

• Will drift be low enough to use it without external position fixes?

Future WorkFuture Work

• Integrate with real-time processor

• Support crawling and running

• Variant with sensors on both feet, and possibly inter-foot ranging sensor as well

• Integrate optical flow, Doppler, or Baro-altimeter sensors

• Tight integration with GPS

• Tight integration with SLAM

• Integrate with real-time processor

• Support crawling and running

• Variant with sensors on both feet, and possibly inter-foot ranging sensor as well

• Integrate optical flow, Doppler, or Baro-altimeter sensors

• Tight integration with GPS

• Tight integration with SLAM

No Silver BulletNo Silver Bullet

• This problem is hard enough to require sensor fusion.

• InterSense has 10 years experience in Kalman filter integration of inertial and aiding sensors (magnetic, acoustic ranging, optical, GPS…)

• We have a generalized sensor fusion core architecture with API for easily integrating new sensors.

• Looking for partners with complementary technologies.

• Thank You!

• This problem is hard enough to require sensor fusion.

• InterSense has 10 years experience in Kalman filter integration of inertial and aiding sensors (magnetic, acoustic ranging, optical, GPS…)

• We have a generalized sensor fusion core architecture with API for easily integrating new sensors.

• Looking for partners with complementary technologies.

• Thank You!