A Positioning Method Combining
Specification of User’s Absolute Position and Dead Reckoning
for Wearable Augmented Reality Systems
Ryuhei TENMOKU Masayuki KANBARA Naokazu YOKOYA
Vision and Media Computing Laboratory
Nara Institute of Science and Technology
8916-5 Takayama, Ikoma, Nara, 630-0192 Japan{ryuhei-t, kanbara, yokoya}@is.naist.jp
Abstract
This paper describes a positioning method for wearable
augmented reality systems. To realize augmented reality
systems, the position and orientation of user’s viewpointshould be obtained in real time. In the proposed method, thesystem measures the orientation of user’s viewpoint by aninertial sensor and the user’s position by combining specification of the user’s absolute position and dead reckoning.
This paper also describes prototype of wearable augmented
reality system using the proposed positioning method.

1 Introduction
Since computers have made remarkable progress in resent years, a wearable computer can be realized[1, 2]. At thesame time, augmented reality(AR), which merges the realand virtual worlds, has received a great deal of attention as a
new method for displaying location-based information[3, 4,5, 6]. Nowadays, augmented reality systems with wearable
computers attract much attention because these systems canbe used in many practical applications[7, 8, 9, 10]. To realize such applications, it is required to measure the user’s
position and orientation in real time. Therefore, some methods of measuring the user’s position and orientation havebeen proposed as the progress of this field.
To realize AR systems, the position and orientation ofusers viewpoint are needed for aligning the real and virtual
coordinate systems. Usually, a Global Positioning System(GPS) is used to measure the users position outdoors. In AR
systems which use the GPS, a real time kinematic GPS[9]or a differential GPS[10] is used to measure the users position accurately. However, since both of them need radio
communication to correct GPS data, the hardware configuration of the system will be complicated. Moreover the GPSdata can be obtained only once a second.
In indoor environments, image markers or tracking sensors are used for estimation of the user’s position and orientation. When we measure the user’s position using image markers[11], the user’s position can be measured at thesame frequency as that of input images. On the other hand,when we use tracking sensors just like electro-magnetic
sensors[12] or ultrasonic sensors, the user’s accurate position (and orientation) can be measured some dozens oftimes or more every second. However, when we apply thepositioning method using image markers for wide environments, so many image markers must be set up. When wetry to apply the positioning method using tracking sensors
for wide environments, we have to set up a lot of expensive
instruments in indoor environments.
In this paper, we propose a positioning method which
can be applied for wide areas easily. The proposed methodmeasures the user’s position by combining the user’s absolute position data which are specified at discrete points andthe user’s dead reckoning data. To specify the user’s absolute position, we use a GPS outdoors, and IrDA markers[13]in indoor environments. Dead reckoning is realized by using a pedometer. The pedometer measures how many steps
and what direction the user walks to estimate the user’s relative movement.
This paper is structured as follows. Section 2 describes
the proposed positioning method based on combining thespecification of the user’s absolute position and dead reckoning in detail. In Section 3, examples of wearable augmented reality systems using the proposed method are described. Finally, Section 4 summarizes the present work.

Specifying absolute position Dead reckoning Figure 1. The proposed positioning method.

(a) IrDA marker.

Figure 3. An example of arranging IrDA markers.

(b) IrDA receiver.

Figure 2. IrDA sensors.

2 Positioning Method Combining User’s Absolute Position and Dead Reckoning
In this section, the proposed method of measuring theuser’s position for wearable augmented reality systems isdescribed. In our method, the user’s position is measured
by combining specification of the user’s absolute positionand dead reckoning data as shown in Figure 1.

2.1 Specification of user’s absolute position
The user’s absolute position is measured using a GPS
outdoors and IrDA devices indoors. IrDA devices consistof IrDA markers and IrDA receivers. Figure 2 (a) and (b)shows an IrDA marker and an IrDA receiver, respectively.
IrDA markers are set up on the ceiling sparsely and always
send their unique position IDs. Figure 3 shows an example of arranging IrDA markers. The user equips an IrDA
receiver which can identify IrDA markers. When the user
comes into the infrared ray range of the IrDA marker, theuser’s position is identified by receiving the position ID withthe IrDA receiver. The infrared ray range of an IrDA marker
is a cone whose diameter is about 3 meters and height isabout 5 meters since the infrared ray has the directivity.
Therefore, when IrDA markers are set up to the ceiling inindoor environments as shown in Figure 3, the infrared ray
range is a circle whose diameter is about 1.5 meter at floor(a) A power
supplying unit.

(b) An example of arranging anIrDA marker with the power
supplying unit.

Figure 4. Power supplying unit for IrDA markers.

level. Consequently, the system can specify the user’s position automatically by passing under an IrDA marker.
Our present IrDA markers are supplied electric powerfrom batteries. It will be an obstacle to applying our proposed method for wide area easily. Accordingly, we aredeveloping electric power supplying units from fluorescentlight lamps on the ceiling. Figure 4 shows a power supplying unit and example of arranging the power supply unit
on the ceiling. By using this power supplying unit, we canarrange and maintain a lot of IrDA markers easily.
When the GPS is used solely for specifying the positionin outdoor environments, the error fluctuates between 5 meters and 50 meters which is caused by various reasons: thenumber of captured GPS satellites, the weather, and so on.
In environments which have no high-rise buildings, the error of the standard GPS is within 20 meters. On the otherhand, IrDA sensors can specify the user’s absolute position
with the error of less than 1.5 meters[13] because the user
can receive the same position ID when the user is in the infrared ray range of the IrDA marker. The GPS and IrDA
markers can specify the user’s position at 1Hz and 250Hz,
respectively.

CameraRealscene
image

QV-700N(Logitech)orientation

Inertial sensor
2INERTIA CUBE
(INTERSENSE)Display device
Clip On Generated
image
Display(Micro Optical)

Dead reckoning module

RelativeMovement(a) DRM-III (PointResearch Corporation)(b) MDP-A3U9(NEC-TOKIN)

Absoluteposition

DRM-III(Point ResearchCorporation)
IrDA receiver
Original(MISystems)

Contents
database
ComputerInterLink
MP-XP7310(Victor)Figure 5. Pedometers.
Figure 6. Example of wearable augmented reality system.

2.2 Estimation of user’s relative movement
We can estimate the user’s relative movement using a pedometer represented by the dead reckoning module, ”DRMIII (Point Research Corporation)” as shown in Figure 5 (a)both indoors and outdoors. The ”DRM-III” estimates theuser’s relative movement by integrating these three data: theuser’s average pace which is input beforehand, the detectionof the user’s walking action, and the user’s walking direction. The cheap and small sensor just like ”MDP-A3U9(NEC-TOKIN)” (Figure 5 (b)) which is composed by acceleration sensors and a digital compass also can estimate
the user’s relative movement. The ”MDP-A3U9” can measure the acceleration of the user’s waist to detect the user’swalking action using the acceleration sensor and measure
the user’s walking direction using the digital compass.
The user’s position can be measured at user’s step rateby using the dead reckoning method with specifying theuser’s absolute position. Therefore, the user’s position canbe measured with the same timing as the user’s movement.
However, the accumulative error occurs according to theuser’s walking distance when we use the proposed deadreckoning method. The accumulative error includes twokinds of errors mainly. One is the difference between theuser’s actual pace and the user’s average pace estimated inadvance, and the other is the difference between the actual
walking direction and the user’s waist direction. Both ofthem are accumulated according to the user’s walking distance. In our method, the accumulative error of dead reckoning is canceled whenever the system receives the position
IDs from IrDA markers or receives the GPS data.

2.3 Combining the absolute position and deadreckoning
In the proposed method, the user’s position is measured
by combining the user’s absolute position which is measured by the GPS or IrDA devices and the user’s relative

movement which is measured by the pedometer. In outdoor
environments, even when the accuracy of the GPS drops
temporarily, the user’s current position is measured by using past GPS data and dead reckoning data. Thus the positioning accuracy is defined as the sum of the GPS accuracy which is included the standard GPS data, NMEA data
and 5% of the distance traveled. The system calculates thevalue for GPS data at every moment and adopts the position
data whose value of positioning accuracy is minimum as theuser’s position. In indoor environments, the user’s position
can be measured in the whole area by combining dead reckoning with the absolute position. In indoor environments,
the user’s position is specified whenever the position IDs
are received from IrDA markers.

3 Example of Wearable Augmented Reality
SystemThis section describes a prototype of wearable augmented reality system using the proposed positioning
method[13]. The prototype system can present locationbased information to the user by displaying virtual object
overlaid images using augmented reality techniques. In thissystem, the user’s orientation which is the other indispensable information for realizing augmented reality is measured using an inertial sensor attached to the user’s head.
Figure 6 shows an example hardware configuration and data
flow of such systems. Figure 7 shows examples of generated images which are presented to the user. Figures 7(a)and (b) show a position-based annotation overlay image indoors and outdoors, respectively. Figures 7(c) and (d) show
images on which a virtual building is overlaid on the realscene of the ruin of the building.

mented Reality. IEEE Computer Graphics and Applications, Vol. 21, No. 6, pp. 34–47, 2001.
[4] S. Feiner, B. MacIntyre, and D. Seligmann.
Knowledge-based Augmented Reality. Communications of the ACM, Vol. 36, No. 7, pp. 52–62, 1993.
(a)

(c)

(b)

(d)

Figure 7. Examples of generated images.

4 SummaryThis paper has described the positioning method combining specification of the user’s absolute position and deadreckoning. In the proposed method, the user’s absolute
position is specified by the GPS or IrDA sensors. Dead
reckoning is realized by measuring the user’s pedestriandata. This paper has also described and example wearable
augmented reality system using the proposed positioning
method.

Acknowledgments
This research is supported in part by Core Research for
Evolutional Science and Technology (CREST) Program“Advanced Media Technology for Everyday Living” ofJapan Science and Technology Agency (JST).

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