A Wearable Computer System with Augmented Reality to Support ...

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egions. A few researchers are investigating largearea augmented reality. Most notable is the work ofSteven Feiner et.al. with Touring Machine project.The Touring Machine allows uses to walk around theColumbia campus and access information via a trackedsee-through display and a hand-held display. Thethree main themes of the their work are as follows:1) presenting University contextual information visuallyconnected to the physical world, 2) supporting arelatively large area in which the user is able to walkaround in, and 3) combining multiple display andinteractiontechnologies. The work presented in this paperextends this concept to a new application, terrestrialnavigation.3 Navigation TaskNavigation is the process which guides movementbetween twopoints, and enables the navigator to knowexactly where they are at any given time. Navigationinvolves position nding, direction nding and measuringdistance. Position nding is typically done byreference to a map { a scaled plan of a portion of theearth's surface. The direction is usually assessed byuse of a magnetic compass. When planning a route,the distances to be travelled between waypoints aredetermined in case position nding is prevented dueto poor feature visibility. Distance can be measuredby pacing or time calculations.Atypical navigation task is to navigate from pointA to point B through a set of waypoints W1...Wn.The user starts at position A and initially navigatesto position W1. Once at waypoint W1, the user thennavigates to position W2. This process continues untilthe nal position B is reached.3.1 Problems with Traditional NavigationNavigation using the above means can be quite dicultand requires considerable training and concentration.Time and attention spent onnavigation meansless attention is paid to the task environment. Thereare many environments where manual navigation isdicult and error prone. The military attempt to copewith this by sharing the navigation task amongst theteam and by training and practice. A novel use ofVirtual Reality is for terrain familiarisation in naturalenvironments [3] where the user can be trained for aparticular set of waypoints.3.2 Global Positioning SystemWith GPS, a navigator applies a similar techniqueto that traditionally used, except for the addition ofaccurate positioning information. The user knowswithin the accuracy of the GPS their current location,thereby greatly enhancing their ability to plot theircurrent position on a map.4 The Wearable Computer SystemThe core of the wearable computer system usedin our experiments is the Phoenix 2 wearable computer[5]. This system has been used in previous experimentsdescribed in [9, 10], involving test on inputdevices for wearable computers.With our current research, the computer systemhas become a lot more complex, with extra peripheralsand more batteries, making it impractical to mounteverything comfortably on a belt. Therefore, a backpackwas used to carry all the needed components, seeFigure 1. The central computer is Phoenix 2 WearableComputer (with a Cyrix 486DX2/66 Processor,32 MB RAM, and a 850 MB 2.5" hard disk drive.)The operating system is Slackware Linux v3.3 runningkernel version 2.0.30. The GPS system is a TrimbleSVeeSix-CM3 GPS Core Module (NMEA-0183 outputand RTCM-104 input), a Aztec RDS3000 DierentialGPS Receiver Module (RTCM-104 output.) The electroniccompass is Precision Navigation TCM2. TheSony PLM-100 dual colour personal LCD monitor isthe see-through device. A VGA to NTSC converterboard is needed since the Sony display requires aNTSC signal.4.1 Software OperationThe main purpose of the software is to use the outputfrom the hardware devices, such as the GPS andcompass, to produce navigation information which isdisplayed to the user, as in Figure 2.To use our system, the user must rst enter a listof waypoints in the form of WGS84 latitude and longitudecoordinate points. Once the waypoints havebeen entered, the user starts the map-in-the-hat program.Keypresses scroll through the current waypointdisplayed on the screen.The compass at the top of the screen in Figure 2shows where the viewer's head is currently pointed,the small triangle underneath with the value indicates
shows the number of GPS satellites in contact withthe receiver.5 TrialsFigure 2: User's screen viewthe exact direction in degrees true 1 . The diamond onthe display represents the waypoint the user is headingtowards, and is positioned relative to the compassat the top of the screen it is meant to approximatewhere the object would be positioned in the physicalworld. However, perspective corrections have not beenimplemented yet and so the diamond will only overlaythe target exactly when the user is looking straight atit. To the right of the diamond is information showingthe name of the waypoint, and its distance and bearing.When the user is within 1000 meters of the nextwaypoint, the size of the diamond cursor increases asthe user approaches the waypoint.To reach the target, the user looks through the displayand attempts to walk to where the diamond islocated. If the diamond is to the left of the displaycentre, then the user rotates their head to the left untilthe diamond is centred on the screen. If the directionto the next waypoint is outside the eld of view, thediamond cursor is placed on the side of the screen andlled with hash marks. The side of the screen the cursoris placed on indicates the direction for the user toturn. The display works in a similar way to the headup display used on military aircraft, where a box isplaced around the target on the display, and the pilotcan y the plane toward the target by keeping it inthe centre of the glass.The bottom left portion of the display shows thecurrent date and time. Under this information is theuser's position as a WGS84 latitude and longitude coordinate.The bottom right portion of the display1 True North is the direction of the shortest global arc thatintersects with the axis of the earth's rotation, and MagneticNorth points in the direction of the horizontal component oftheearth's magnetic eld at its current location, and not actuallyto True North.We performed three eld trials of our navigationsystem to test the system in a realistic outdoor setting.The trials tested three dierent conditions: waypointsa large distance apart, a large set of waypoints, andwaypoints in an urban setting. The limitations of theSONY display power consumption forced us to limitthe trials to no longer than 2.5 hours each.5.1 Trial 1 { Long DistancesThe rst trial was between waypoints a large distanceapart with obstacles between them, such asbuildings to force us to deviate from the prescribedbearing. This trial included waypoints roughly a distanceof 1.7 kilometres maximum from the startingposition. Because the display has a battery life ofonly 2.5 hours, this trial only tested a start, middleand end waypoint.The navigation system provided accurate bearingand distance information to all three waypoints. Deviationswhile walking were needed to be undertakento avoid construction works, and the navigation systembehaving accordingly. The accuracy obtained wasto 5 to 20 metres. A problem we noted was that sometimesthe GPS signal would completely disappear inopen terrain with no discernible features blocking thesignal, but after a moment ortwo the signal was reacquired.5.2 Trial 2 { Large Data SetThe second trail used six waypoints, derived fromsurvey markers and within a kilometre of each other.The rst three waypoints were within a 30 metreradius of each other, to test the system's accuracy.Unfortunately, only20 metre accuracy was achieved.These points were under a set of high-tension powerlines,and this may have been the cause of the pooraccuracy, as the dierential GPS signal was carried ona radio signal.On the nal three waypoints, about 400 metersapart, we were able to achieve an accuracy of metresfor two of them and 17 metres for the other. Lighttree cover on occasions interfered with the GPS signal,and like the previous trial, the signal was lost fora short period of time out in the open with no blockingterrain.
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