WO2011005080A1

WO2011005080A1 - Three dimensional tracking system and method

Info

Publication number: WO2011005080A1
Application number: PCT/NL2010/050327
Authority: WO
Inventors: Marco Otte; Johan F. Hoorn
Original assignee: Vereniging voor Christelijik Hoger Onderwijs Wetenschappelijk Onderzoek en Patientenzorg
Current assignee: Vereniging voor Christelijik Hoger Onderwijs Wetenschappelijk Onderzoek en Patientenzorg
Priority date: 2009-07-06
Filing date: 2010-05-31
Publication date: 2011-01-13
Anticipated expiration: 2012-01-06

Abstract

During object movement tracking, such as tracking movement of a human head, infrared sensors at different locations are used to detect view angles to one or more light sources on the object. A distance from the sensors is calculated from the view angles. The light sources each contain a plurality of infrared light emitters oriented to generate a disk of light. In the example wherein the light sources are attached to the head and plane of the disc is oriented horizontally, this means that the light sources will remain visible from horizontally directed sensors during most head movements. In an embodiment the light source or light sources are attached above the head, mounted on a rod that is attached to the head, preferably at different heights if more than one light source is used.

Description

Title: Three dimensional tracking system and method FIELD OF THE INVENTION

The present disclosure relates to a system and method for providing three-dimensional tracking, e.g., site surveying for wireless motion tracking. The disclosure also relates to a head mountable device for use in such a system.

BACKGROUND INFORMATION Tracking users in three dimensions usually utilizes expensive machineries such as the Polhemus system (Polhemus), which generally relies on magnetic markers. These systems are not only expensive, but they are complex to set up and maintain, making it infeasible as a solution for an easy- to-use and adaptive system (LaViola, 2008— referenced herein below).

The use of infrared emitters and receivers for tracking a user's position is primarily done in gaming. The Nintendo WII gaming console is one of the known applications of the technique. The Nintendo WII gaming console uses a handheld device, also called Wllmote, that comprises an infrared camera that produces images representing infrared light intensity at respective positions in an array of pixel positions. From a peak in the intensity as a function of pixel position, a pixel position can be determined at which a light source is visible in the image. However, the IR functionality of the WII system is primarily used as a pointing device and not as a tracking device, like we use it.

Since the introduction of the Nintendo WII game console with its remote controllers, there has been considerable attention to the possible uses of this system beyond its intended use (Peek, 2009 (b) - referenced herein below) . Significant activity, however, does not generally arise from professional researchers, but from end-users, resulting in a small number of published papers on the possibilities of the WII-motes. Both the internal accelerometers (Slyper and Hodgins, 2008— referenced herein below) and the infrared camera of the WII-mote having received attention in alternative uses. One such discussion has come from a particular paper, which address the WII alteration movement (Lee 2008 (a), and Lee 2008 (b)— referenced herein below).

Although significant discussion has been about the use of the infrared sensor of the WII-mote, very little has been professionally researched. There have been several conference and student papers, most of which are unpublished work. Investigators usually place one single WII-mote near a display monitor to track a user's relative position and employ this as an alternative input device (as described in Pensyl et al., 2008; Sreedharam, Zurita, and Plimmer, 2007; Tamai et al., 2008— referenced herein below). Others publications have made certain incremental adjustments to systems described in the Lee publications (Chow, 2009; Nunnally, 2008; Schou and Gardner, 2007; Shirai, Geslin, and Richir, 2007; Vural, Tekkaya, and Erogul, 2008; Yim, Qui, and Nicholas Graham, 2008 - referenced herein below), focused on the mathematical approach to extract real world data from the WII- motes (Dehling, 2008; Rickard and Davis, 2009— referenced herein below), created musical applications (Paine, 2007 - referenced herein below), detected gestures (Grubert, Carpendale, and Isenberg, 2008; Schlomer et al., 2008 - referenced herein below), or controlled robots (Filippi, 2007; Guo and Sharlin, 2007 - referenced herein below) with a WII-mote. Several examples were found where the author explored the assistive possibilities of the WII-mote in both learning and medical applications (Battersby, 2008; Dale et al., 2008).

Few publications described actual prototype systems that track users in some way (Battersby, 2008; Birgisson and Kristjansson, 2008;

Slechtweg, Mohler, and van Liere, 2008 - referenced herein below). Further studies used the similar principle described herein, with two WII-motes as receivers and single or multiple IR LEDs as emitters worn by users. The description provided in Battersby (2008) - referenced herein below, however, used only one set of LEDs mounted in front of the user's head, thereby limiting the measurable data (X, Y, Z, but without rotation) and the freedom of the user (e.g., 360° rotation would be unlikely or even impossible to achieve because the head obstructs the signal). The description provided in Slechtweg (2008)— referenced herein below - used his setup to control a mini-CAVE where the user sits inside the system and may not be able to move around. The layout of the LEDs on the back of the head makes it unlikely or even impossible to track 360° rotation.

U.S. Patent Publication No. 2009/0033623 (the "623 Publication") describes a more general system of infrared emitters and receivers to function as measuring and analyzing system of three-dimensional movement and "virtual input and simulator" (Lin, 2009— referenced herein below).

Accordingly, there may be a need to address and/or overcome at least some of the deficiencies described herein above.

SUMMARY One of the objects of the present invention is to address at least some of the deficiencies of the prior art, and to provide exemplary

embodiments of systems, methods and computer accessible medium for providing three-dimensional tracking.

A system for three-dimensional object tracking as claimed in claim 1 is provided. Herein a light source comprising a plurality of infrared light emitters is used that are directed in different directions over at least a 180 degree angle range. A first and second sensor each determine a view angle to the first light source. Preferably the infrared light emitters are located so closely together that they are detected by the sensors as a single blob. Use of infrared emitters makes the light source less distracting for users and easier to detect. By using a plurality of infrared emitters directed in different directions it is made possible to provide for relatively high light intensity that can be robustly detected even if the light source is rotated.

In an embodiment the light emitters are directed at successive angles in a 360 degree angle range along a disk. Thus the light source can be rotated over 360 degrees and still remain detectable for the sensors. A disc comprising nine IRLEDs may be used for example covering emission over 360° in the XY-plane and between 20°-30° in the Z-plane.

In an embodiment the system comprises a light source carrier on which the first light source and a second light source are mounted at a predetermined relative position at mutually different heights. The different heights ensure that the light sources will not block each other when they are viewed by the sensors directed along a substantially horizontal plane. Also it makes it easier to identify the individual light sources. Thus, the coordinates of both light sources can be determined with the same sensors and from this an orientation orientation angle of a line between the light sources can be determined.

In a further embodiment the light sources may be placed on a head mountable device for use on a user's head. In this case the first and second light source may be mounted at mutually different heights above the head. In this way the view of the light sources from the sensors will not be obstructed by the head when they are viewed by the sensors directed along a substantially horizontal plane. The head mounted device may comprise a cap or a pair of glasses for example. A rod extending upwards from the position of the head may be used to mount the light sources above the head, to avoid obstruction. In a further embodiment an arched rod is used, extending in an arch over the head from positions on mutually opposite sides of the head. This provides for a stable mounting of the light sources. Different light sources may be located on different uprights of the arch for example, to provide for horizontal spacing. In an embodiment the infrared emitters may be continuous narrow band devices, such as infrared LEDs. 940 nm infrared emitters may be used for example.

In an embodiment the system comprises a platform with the first and second sensor mounted at stationary locations on a platform. Thus it can be ensured that the sensors remain at fixed position and orientation during a series of measurements. In a further embodiment the platform is adjustable in height and has a moveable sensor holder that determines the angle of the first sensor relative to the baseline. This makes it easy to realize a desired configuration of sensors. The first and second sensor may comprise infrared receivers, sensitive to infrared light. Preferably sensors are used that are insensitive to visible light. Thus disturbance of sensing by visible light sources is avoided. WII remote controllers may be used as sensors.

In an embodiment a head mountable device is provided to facilitate tracking head movements. In this embodiment the first light source on the head mountable device may be used in combination with the sensors to track head movements. The sensors are directed so that y pixel coordinates of the sensors are responsive to the height of the location of the first light source and x pixel coordinates are responsive to the location in a direction transverse to the height. The first light source is located above the head. In an embodiment the head mountable device comprises a rod that extends above the head. The first light source and optionally the second light sources are located on the rod above the head. As a result of the location above the head, the line of sight from the sensors to the light sources is not intercepted by the head during normal head movements. Furthermore, as the first light source and the optional second light source comprise a plurality of infrared emitters directed in mutually different directions in a plane transverse to the height direction, it is avoided that rotations of the head around that direction have the effect that the sensors view the light sources from a direction in which they do not emit light, or at least the angle range of such rotations is reduced. When the emitters cover a 360 degree angle range no rotations of the head around the vertical has the effect the sensors view the light sources from a direction in which they do not emit light. When the emitters cover a 180 degree angle range rotations of the head do not have this effect as long as the head is not fully turned around.

Certain Exemplary differences between the exemplary embodiments of the system, method and computer-accessible medium and the one in the '623 Publication can be as follows:

i. The '623 Publication describes pulsating and/or different wavelength and/or intensity sources as emitters to distinguish between the emitters, whereas the exemplary embodiments of the present disclosure can utilize emitters that continuously send a single wavelength and can be placed at different heights on the user. Such additional requirements of the '623 Publication complicates the entire system considerably, making it likely error-prone and expensive.

ii. Instead of basic trigonometry, the '623

Publication describes the use of complicated calculations because of the wavelengths and/or pulsating emitters. This can increase the error and can make the entire system error-prone.

iii. The '623 Publication describes the use of one or multiple receivers at a known (x, y, z) location, whereas the exemplary embodiments of the present disclosure can have two or more receivers that can be placed anywhere and merely need to know the distance between the receivers. Having the knowledge of the real world (x,y,z) coordinate of the receiver(s) makes setup of the '623 Publication complex and can lead to errors. The exemplary embodiments of the system does not require a complex setup, and can use only the distance between both receivers and their angle towards the connecting line.

iv. The '623 Publication describes the use of a sub- system to correct for background (ambient) light, whereas for the exemplary embodiments of the systems of the present disclosure, no correction is needed, which can make the exemplary system simpler and less error-prone. Using a correction for background light can offer protection to erroneous reading, and also increase the chances of missing a weaker signal. The exemplary system of the present disclosure can be only sensitive to infrared light so that limited attention needs to be paid to avoiding erroneous signals.

v. Patent focuses on the visible light part of the spectrum (400— 1000 nm) although near infrared is included, whereas the exemplary embodiments of the system according to the present disclosure can utilizes, e.g., 940 nm infrared emitters. Using, e.g., infrared light emitters can be less distracting for users.

vi. The '623 Publication describes the use for machine input, gestures, gaming (devices), whereas the exemplary

embodiments of the system according to the present disclosure can be used in virtually any situation where tracking is needed or preferred. The exemplary system can focus on three-dimensional tracking without limiting its

applications.

vii. The '623 Publication describes the use of receivers having a rotation mechanism to follow the emitters, whereas the receivers provided with the exemplary embodiments of the system according to the present disclosure can remain stationary. Using a rotation mechanism can add complexity, expense, and points of failure.

In particular, exemplary embodiments of a light-weight, wireless, and moderately-priced three-dimensional tracking system, which can be referred, but in no way limited, to "3D Site Surveyor", can be provided. Such exemplary embodiments can facilitate a versatile, hands-free, and easy-to-use human- computer interaction, combining currently- available (e.g., off-the-shelf) hardware with custom-made software. For example, such exemplary embodiments can be based on the presently-available Nintendo WII remote controller hardware. The exemplary embodiments of the 3D Site Surveyor can be used to detect movement of a user in three dimensions (X-, Y-, and Z-axis), including rotation in the XY-plane (yaw). In particular, it is possible to also measure pitch and roll, making the exemplary embodiments facilitate the detection of, e.g., 6DOV. The exemplary system, method and computer - accessible medium can be used in, for example, gaming, virtual reality, ambient assisted living, and academic research (e.g., human motion, perception, and attention).

According to one exemplary embodiment of the present disclosure, the system, method and computer-accessible medium can facilitate the tracking of movement of users in three dimensions, while walking around freely. This can be done, e.g., by using two small discs with infrared light- emitting diodes (IR LEDs or IREDs), which can be attached to either a cap or a pair of safety glasses. The exemplary discs can be placed at different heights on the left and right side of the user's head to ensure continuous tracking of both IR sources. The IREDs, nine per disc, can cover, e.g., about 360° or more in the XY-plane and about 20°- 30° in the Z-plane, other configurations are certainly available, and are in the scope of the exemplary embodiments of the present disclosure.

The exemplary discs can be powered, e.g., by two 9V batteries or other batteries or power sources (whether rechargeable or not), and the emitter section of the exemplary system can be lightweight and portable. The exemplary receivers can include over-the-counter Nintendo WII Remote Controllers (see Ikeda et al., 2007 - referenced herein below), or WII-motes for short. The WII-motes (e.g., two or four) can be placed at a known distance from each other and at a known angle from the baseline that connects them. A standard Bluetooth interface can connect the WII-motes wirelessly to the controlling computer.

For example, exemplary C# software according to the exemplary embodiments of the present disclosure can be provided, which may use the publicly and freely available WII-mote Lib dynamic link library (Peek, 2009(a) - referenced herein below), can be used for querying the Wll-motes at customizable high-speed intervals (e.g., up to about 1 ms). The exemplary software can generate either raw sensor data to be analyzed and processed at a later point and/or direct real world X, Y, Z coordinates as well as Yaw (angle in the XY-plane). In determining the real world coordinates and angles, the exemplary software can use triangulation and trigonometry techniques.

Further, the (raw) data can be used to determine derivatives of the position and angle, such as velocity, acceleration as well as angular speed and acceleration.

The exemplary embodiments of the present disclosure can also include the so-called WII-Stakes, which are platforms to hold the Wll-motes. Such WII-Stakes can be adjustable in height and have a moveable WII-mote holder that can determine the angle of the WII-mote towards the baseline.

The exemplary embodiments of the system, method and computer-accessible medium can facilitate the users to freely and wirelessly move inside the viewable area of the Wll-motes and tracks their position and the angle of their head to sub-centimeter accuracy.

For example, certain exemplary embodiments of the present disclosure utilize at least two light sources, e.g., small discs (4 cm in diameter), each with 9 high-power, wide-angle IR-LEDs; which IR sources are raised to a position above the user's head and placed at a different height from one another so that each source can be tracked individually, providing for the angle of the user's head to be tracked by calculating the angle that the line between the two sources has toward the baseline. Additional exemplary systems can utilize WII-Stakes, which are platforms to hold the Wll-motes, such platforms being adjustable in height and having a moveable WII-mote holder that determines the angle of the WII-mote towards the baseline.

According to still additional exemplary embodiments of the present disclosure, when a point is lost or could not be tracked, another point can still be tracked on the same sensor index, making it relatively easy to pick up the lost point as soon as it reappears. Further exemplary embodiments provide a support of a free movement and 360 rotation (yaw), which can be extendible to true 6 DOV (e.g., through the addition of pitch and roll detection). Further, according to additional exemplary embodiments, it is possible to use, e.g., four WII-motes which can provide a much greater range.

Brief description of the drawing

These and other objects, features and advantages of the exemplary embodiment of the present disclosure will become apparent upon reading the following detailed description of the exemplary embodiments of the present disclosure, using the following figures.

Figure 1 shows an XY plane with two IR emitters

Figure 2 shows a WII stake

Figure 3 shows viewing areas

Figure 4 shows determination of height of a point

Figure 5 shows determination of angle from the baseline

Figure 6 shows safety goggles with LEDs

Figure 7 shows a screen dump of a WII test program Figure 8 shows a triangle of LEDs

Figure 9 shows a diagram of angles to determine delta

Figure 10 shows LED discs on an arch

Figure 11 shows LED discs on a cap

Figure 12 shows raw data of X-coordinates

Figure 13 shows interpolated data

Figure 14 shows an extended range when using four WIImotes DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

According to the exemplary embodiments of the present disclosure, a system, method and computer-accessible medium can be provided which facilitates tracking of the user's XYZ-position and the angular position of the head (in the XY-plane). The angular position can be measured as degrees from a predefined baseline and therefore gives values ranging from about 0° to 359° (as shown in Figure 1). In this embodiment the system and method make use of at least one infrared light source and a plurality of sensors for sensing the direction of light received from the infrared light source or light sources.

Embodiments will be described wherein the sensors are WII motes, available for the well known WII game system, but it will be understood that, where a WII mote is mentioned any technically similar sensor may be used. Each WII mote comprises a camera with pixels on which infrared light from the light sources can be detected, at a pixel with pixel coordinates that depend on the direction of the light source.

There are several exemplary ways of tracking points in three- dimensional space. It is possible, and within the present disclosure, to use one sensor point. This can be done, e.g., by tracking of three or four IR light sources, at known positions relative to each other. In another exemplary four IR- source version, sources can be positioned in a regular tetrahedron. The exemplary embodiment which can utilize three and four sources can make use of quartic equations and use rather messy but workable solutions (Rieck, 2008 - referenced herein below).

Another exemplary way of tracking points in three-dimensions is to compare the apparent distance between two emitters on the receiver sensor with the actual real distance between the emitters. This exemplary procedure may certain drawbacks, because it can assume that the emitters are more or less in the centre between the receivers and consequently, keep the user from moving around freely. There is, however, a number of exemplary issues with these approaches. The three IR-sources exemplary embodiment may have difficulty of reliably detecting, e.g., all three sources at all times, due to the limited viewing angle of the sensor, e.g. a WII-mote. For example, it is possible to us two or more WII-motes to cover enough angular rotation of the head. This can lead to detection problems in the area where the IR sources shift detection from one Wiimote to the other. Because the WII-motes generally assign detected IR sources to the first available empty sensor slot (WII-Brew, 2006— referenced herein below), it can be difficult to reliably detect and follow three IR sources at all times. Further, the exemplary mathematical solutions may not indicate which solution belongs to which point, making it difficult to accurately assign these values and have reliable data (Rieck, 2008). The four IR-sources exemplary embodiment of the system likely uses a regular tetrahedron setup of the IR sources. There may be certain issues in attaching this device to a user's head. In addition, this exemplary embodiment can detect four IR sources at all times, which can cause issues when two IR sources are in the same viewing line, reducing the number of detected IR sources to three. Again, as provided in the exemplary three IR-sources setup, there may be issues when switching from one to the other WII-mote.

According to an exemplary embodiment of the present disclosure, it is possible to use two WII-motes and triangulate the location of the IR sources in the 2D XY-plane. Certain publications (Chow, 2009; Dehling, 2008 - referenced herein below) allege some accuracy limitations with triangulated data from the WII-mote cameras, no problems were apparent with the reliability nor the accuracy of the signal during testing. There can be issues with controlling the surrounding IR radiation and the sporadic drops in detected signal, but these issues are easily compensated for (as described herein below).

To connect the computer that runs the exemplary C# program to the WII-motes, it is possible to use, e.g., a Trust USB dongle with the Trust Bluetooth Manager. Steady and continuous connections have been with each Wll-mote, contrary to the issues previously experience with USB dongles on Windows XP (Lee, 2008b; Wiimote_Project, 2008— referenced herein below).

To make sure the Wll-motes are in the correct position, it is possible to provide so-called WII-Stakes (as shown in Figure 2). These exemplary devices can be standards made of wood with a square base (e.g., approx.

30x30cm), a stake, and a small platform (e.g., approximately 20x20cm) on which the Wll-mote can be placed. A wooden hook on the platform can be fixed at known angles from the baseline. The WII-Stake can provide that the WII- mote sensor may be at about 150cm height, at the correct angle from the baseline (e.g., the wall).

Figure 1 shows the XY-plane with x and y direction and angle (Greek delta) made by the two IR emitters Pl and P2. It is possible to place, e.g., two Wll-motes at a known distance from each other (Figure 1), which formed the baseline. The angle can be determined from the baseline

(OffsetAngle) at which the Wll-motes are placed. In this exemplary manner, it is possible to determine the workable area of the setup (as shown in Figure 3). When both Wll-motes detected the same IR source, it is possible to read out the X-coordinate from the direction of the baseline (e.g., for Wll-mote 1 shown in Figure 3, this can be the X-coordinate; and for Wll-mote 2, this can be 1023- X). Because the resolution in the X-direction (e.g., 1024) and the viewing angle (e.g., 40°) is known, it is possible to determine the view angle per pixel on the sensor.

2

Rod perPixel ≡6.8 x\0^→rad≡ 0.039°

1024

On this basis, it is possible to calculate the theoretical accuracy of the exemplary system at different distances. Examples are in Table 1. Table 1 Distances and accuracy in position

Then, it is possible to calculate the angle of the IR source from the baseline:

a = X * rad_perPιxel + OffsetAngle

In doing so for both Wll-motes, it is possible to obtain, e.g., two angles (Alpha and Beta) and together with the baseline triangulated the orthogonal distance (D shown in Figure 1) from the baseline to the IR source:

baseline * sin(a) * sin(/?)

sin(a + β)

On this basis, it is possible to use trigonometry to calculate the X and Y coordinates, taking WII-mote 1 as the origin.

D

Jl = - sin(α)

X = b\ Y = D

For the height (z-coordinate), it is possible to apply the same or similar principles of measuring the number of y-pixels and using the known angle of view (e.g., vertically 25°, empirically found). Adding the known height of the Wll-motes, WII-Height can provide the height of the LED-discs (8) (as shown in Figure 4). Z = WiiHeight + d\ * tan(384 - Y) * rad _perPlxelVert

To track the angle of a user's head, two IR sources can be used. By triangulating both sources, it is possible to calculate the angle that the line between the two sources had towards the baseline. To do so, it is possible to use the (x,y) coordinates of both points (Pl and P2) (9) (as shown in Figure 5):

Further, the quadrant in which the angle occurred can be determined. This can be deducted from the sign of the (P2y— Ply) and (P2x— PIx).

CONSTRUCTION OF EXEMPLARY IR SOURCE DEVICE

For example, to construct an exemplary IR source device, goggles were implemented and two LEDs were provided (as shown in Figure 6), which can be turned on and off separately. The normal visible light LEDs was replaced with IR LEDs. The freely available WII-Lib dynamic link library (Wiimote_Project, 2008— referenced herein below) has been used to test our setup (as shown in Figure 7). Although the WII- mote did detect the exemplary IR sources, the rotation angle of the head was limited, for example. The standard IR LEDs (mostly used for remote controls) have a limited emitting angle (around 20°). For example, the goggles can be covered with more LEDs to cover more area or it is possible use more WII-motes.

Yet, the WII-mote library can limit the number of WII-motes to four and a total of four WII-motes can be used to eventually extend the viewable area. Therefore, the exemplary multiple LED solution has been implemented. For example, a Speedlink WII Sensor Bar (WII-Bar for short) was used, which has two groups of three LEDs. Each of these LEDs had an emitter angle of about 70°, which can mean that fewer LEDs sufficed to cover a large enough area. The initial WII-Bar tests, without the goggles, showed that although the usable angle was better, it was still less than optimal to guarantee that both Wll-motes can detect the IR sources at all times. Therefore, we disassembled two WII-Bars and positioned the boards in a triangle, thus increasing the total area coverage by the LEDs to over 180° (as shown in Figure 8). Then, the WII-Bars were to the goggles.

Further, the angle towards the baseline of the two IR sources, or the angle of the user's head was determined. Because the distance between the two IR sources in the real world was known (e.g., in exemplary case, about 15cm) and because the distance observed by the WII-mote cameras was calculated, a relation was established between distance, angle, and the ratio between real distance versus observed distance of the IR sources (as shown in Figure 9). To determine the relationship between observed distance and real distance between the IR sources, the two IR sources were placed such that their connecting line was orthogonal to the central viewing axis of the WII- mote. It was understood that further corrections may be made if the IR sources moved away from this central axis. It was determined that there is a simple relation between the observed and real world distances of the IR sources:

This calculus found the angle (d in Figure 9) between the line of the

IR sources and the central viewing axis of the WII-mote. However, it was difficult to determine the sign of the angle. The observed IR sources were at the same sensor X-coordinate because the IR sources were projected onto the imaging plane of the WII-mote camera (Pl=Pl' and P2=P2' in Figure 9).

Additionally, because one IR source was seen with WII-mote 2, it may not have been possible to accurately determine the orientation of the user's head for a large part of the intended range.

To solve this issue, both IR sources were made, e.g., always visible for both Wll-motes. This can facilitate two triangulated points from which the angle could easily be determined. Therefore, the IR sources were raised to a position above the user's head and placed each IR source at a different height so that one source could not easily block the other source behind it (as shown in Figure 10) and it would be possible to track each point individually. Two small discs (e.g., 4cm in diameter) were provided, each with 9 high-power, wide-angle IR-LEDs (1.2V) at 40° distance from each other (see Figure 10). These discs emitted a powerful 360° IR field that was seen by the WII-motes as one 'blob'. Each IR-LED disc was fed by a 9V battery. With each disc at a different elevation (10/15cm apart) and by placing the discs above the user's head, a tracking signal was establish throughout the visible area of the WII- motes, no matter what the angle of the user's head was (in the XY-plane).

To make the exemplary system more wearable and less obtrusive, the arched rod was mounted with the LED-discs on a baseball cap. The 9V batteries were stashed in a small box that the subject could clip onto a belt or any other piece of clothing (as shown in Figure 11).

According to one exemplary embodiment of the present disclosure, the exemplary system can use two or more LED-discs. For example, it is possible to solder, e.g., nine (9) LEDs onto a small circuit board including a resistor to prevent overloading the LEDs. To complete the exemplary LED- discs, the array of LEDs can be connected to a standard 9V battery which can be enclosed in a wearable container. The exemplary construction of the support for the LED-discs can take several forms. For example, an aluminum arch can be utilized, and bend into shape and attached to any wearable accessory (e.g., cap, goggles). The construction of the WII-Stakes can involve cutting the used material (e.g., wood, metal) into the correct dimensions and shapes, and attaching the pieces together using standard materials (e.g., nails, screws). EXEMPLARY SAMPLING PROGRAM

To gather the data detected by the Wll-motes, an exemplary embodiment of a program in C# can provided, using the free Microsoft Visual C# Express Edition (Microsoft, 2008). To interface with the WII-mote, it is possible to provide the freely available WII-moteLib to our project (Peek, 2009 (a) - referenced herein below). It should be understood that such exemplary program can be provided on or stored in a computer-accessible medium, such as a hard drive, floppy disk, RAM, ROM, CD-ROM, memory stick, and/or any other storage device. In particular, when such software program is accessed by a processing (or computer) arrangement, such arrangement can be configured to execute the exemplary program.

After initializing several constants and variables, the exemplary program can open the user interface and checks how many Wll-motes are connected to the PC. These Wll-motes can be stored in special variables that check which WII-mote is currently sending information. Then a timer can be initialized, which can control when the exemplary program writes data to the log file. C# and Windows can facilitate for ticks as small as, e.g., lms.

To handle all the different threads, separate routines deal with the interface, the Wll-motes, the log file, and the timer. After that, the program operates on the created event handler for the timer.

When the set period of milliseconds has elapsed, the exemplary program can trigger a new event and goes through a set of methods (code) to 1) get the raw X and Y coordinates from the Wll-motes, 2) check if something needs to be done about the (visual) stimulus, and 3) write all the relevant data (time in ms, the raw (X, Y) -coordinates of points Pl and P2 from both WII- motes) to the log file. EXEMPLAEY TEST RESULTS

The initial exemplary tests of 3D Site Surveyor demonstrated that the WII-motes can sometimes lose one of the LED-discs for a short period of time (as shown in Figure 12). Usually, these drops only last one or two cycles (e.g., 10-20ms. When a point is lost, the other point is still tracked on the same sensor index, making it easy to pick up the lost point as soon as it reappears.

To avoid signal loss, i the sensitivity of the WII-mote's IR camera was increased to its maximum. This can mean that the sensor will pick up stray IR signals or reflections more quickly, which urges to clear the environment from additional IR sources or reflective surfaces.

Only seldom, signal can drop can occur when the aluminum rod that holds the LED-discs blocks the signal or when the user tilts his or her head too far and blocks the signal with the head. This can be resolved, e.g., by user instructions.

To obtain a relative accuracy of the exemplary 3D Site Surveyor, the IRED was moved about lcm into the Y-direction (e.g., 2 trials, 20

measurement points, real world) and recorded the results with our sampling program. Then, the differences were compared between the real-world differences vs. the measured differences. Mean deviation of the differences was about .0066cm (SD = .46cm). In absolute values, the mean deviation was .40cm (SD = .45). Thus, the exemplary 3D Site Surveyor measures at the sub centimeter level with a resolution of about 5mm.

EXEMPLARY RESULTS SUBSEQUENT TO SAMPLING

After sampling, the data files that contain the raw coordinates was processed. To recover the missing values that occur when one of the LED-discs is temporarily lost, an exemplary embodiment of a data- correction filter according to the present disclosure was provided. This exemplary filter scans the raw data and uses a weighted average for any points that are recorded as missing (e.g., '9999' is written for the x-and y-coordinate in case a WII-mote loses a point). For a three record loss (30ms) of the signal, the exemplary calculation runs as follows:

Given points A-B-C-D-E, where points B-C-D are lost and recorded as (9999,9999), points B-C-D are reconstructed as:

+ 2X_E + 2Y_E

Xc - Yc

4 4

Or more generic:

P_m = ((n - im - 1)) * P_n-1) + dm - 1) * P_n__λ)

Where n is the number of missing points. Pm is one of the missing points and m is between 1 and n. With the missing point recovered, the real world coordinates (x,y,z) can be calculated, using the aforementioned formulas. Additionally, the angle towards the baseline is calculated and these real world data are written to a new data file to be used in further analysis (as shown in Figure 13). EXEMPLARY CONCLUSION

Most of the advanced 3D tracking systems that are currently on the market use RF or magneto-systems to detect and track positional information. Few systems are available that have limited 3D tracking of movement, mostly in gaming (NaturalPoint, 2008 - referenced herein below). The more professional systems have the disadvantage of 1) being expensive, 2) harder to setup (calibration), 3) requiring special software, and 4) requiring special hardware.

The products that are aimed at the consumer 1) lack functionality because systems are used for a particular application (e.g., certain games), 2) do not support 360° rotation, 3) do not support truly free movement, and 4) have a very limited range (no more than 150cm).

The exemplary embodiments of 3D Site Surveyor according to the present disclosure can, e.g., 1) be cheap, 2) be easy to set up, 3) support free movement, 4) support 360° or more rotation (yaw), which can be extendable to true 6DOV, 5) use standard Windows PC hardware, 6) utilized an exemplary program that can function as stepping stone for a) be an input simulator or b) direct control of other software and hardware, and 7) has a medium range (depending on the number of receivers used and the length of the baseline between 4 and 10 meters perpendicular to the baseline).

It is also possible to use four instead of two WII-motes. This exemplary embodiment can facilitate that the exemplary system would have a significantly greater range (as shown in Figure 14).

In an embodiment a first and second WII mote as described in the preceding are used, placed at the same height at different positions in the horizontal plane, separated by the base line, and directed at an angle to the base line. A third and fourth WII mote may be added, for example at the same horizontal positions as the first and second WII mote respectively, but at a different height. The third and fourth WII mote may be directed differently from the first and second WII mote respectively. Instead of the detected pixel positions of the light sources at the first WII mode, detected pixel positions of the light sources at the first and third WII mode are used. As a result a combined angle range in the horizontal plane is available. More WII motes may be added to increase this range. A similar extension of the angle range applies with respect to the second and third light source. The different Wll-motes may be placed at different height. In an embodiment the added third and fourth WII motes are directed so that their fields of view cover angle ranges adjacent the angle ranges covered by the field of view of the first and second WII motes. Preferably, the WII motes are directed so that Wll-motes whose fields of view cover adjacent angle ranges have overlapping fields of view, e.g. with an overlap angle range of two degrees. This ensures that no signal loss will occur. When light sources are detected at corresponding pixel positions in the first and third WII mote near the edges, where the ranges overlap, one of these detections is discarded. The same goes for the second and fourth WII-mote.

In an embodiment the first and second WII motes were directed so that the edges of their angle range made an angle of 10 and 50 degrees with the base line respectively. The first and second WII motes were directed so that the edges of their angle range made an angle of 48 and 88 degrees with the base line respectively. This provides for a large working area. Other angles may used, for example when sensors are used that have a different field of view. Preferably, sufficient sensors are used to provide for an angle range that reaches up to an angle of at least substantially ninety degrees relative to the base line.

User movement can result in changes in six degrees of freedom, corresponding to translations in three dimensional space and rotation in three dimensional space. The number of degrees that can be determined depends on the number of light sources. When it is desirable to measure six degrees of freedom, three light sources may be used. In an embodiment, a third disc was placed on top of the arch directed horizontally, with the central directions of emission of the LED's directed at successive angles in a horizontal plane. Other positions of the third light source at a height different from that of the other light sources may be used.

In an embodiment the rotation angles were determined by the steps of determining the centre of rotation in real world coordinates, determining a rotation matrix and deriving angles of rotation from the rotation matrix. For head movement, the centre of rotation may be taken to be top of the spine, that is, a position midway between the ears. This position has a fixed relation to the arch given the way in which the arch is attached to the cap or the pair of glasses. The distances of the light sources to this position are also fixed and known. This allows the centre of rotation to be determined from the observed 3D positions of the light sources and the distances. Subsequently, the the observed 3D positions of the light sources and the centre of rotation were used to determine the rotation matrix.

Preferably, a calibration step is performed wherein the WII-motes are accurately positioned and directed according to the base line and camera direction angles assumed in the computation, or wherein the base line and camera direction angles for use in the computation are adapted according to calibration measurements. Calibration measurements may be performed using calibration light sources at known positions. In an embodiment a light source fixed at a predetermined location on the WII-mote platform was added for calibration purposes. Measurements of the direction in which this light source is detected may be used to determine the direction of the WII-motes and baseline between them, or to guide changes in the setup of the position and direction of the WII-motes until the detected direction of the light source corresponds to a predetermined setup.

In an embodiment, a plurality of users may be tracked using the same set of WII-motes. Users may be provided with light sources that emit light in mutually different infrared wavelength ranges for example, so that light detection from different users can be distinguished on the basis of the wavelength, for example by applying different filters. Alternatively, the head mount of each user may be provided with a modulator circuit configured to apply a characteristic temporal variation on an electric signal that controls the intensity of the light sources. Correspondingly, a detector may be used to distinguish detected light sources of different users by comparing the received temporal pattern of light variation with characteristic temporal variations defined for different users. This may be used to select between different detections. Based on the selected detections position calculations for different users may be performed.

To summarize, the exemplary embodiments of the 3D Site Surveyor according to the present disclosure can be precise, wireless, facilitate 360° rotation, inexpensive, use little power, and/or employs limited and light-weight gear. The exemplary embodiments of the present disclosure can be used for analyzing human posture, stance and movement with and without external stimuli. Such exemplary embodiments can also track people in virtual environments and use the positioning data for the real time rendering of the virtual environment. When attached to 2D or 3D video projecting glasses (commercially available), the exemplary system can be used to control any digital system such a games, robots, and operating systems. When attached to a robot, the exemplary system can be used to control the robot within the viewable area of the receivers.

The foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the present invention. In addition, to the extent that the prior art knowledge has not been explicitly incorporated by reference herein above, it is explicitly being incorporated herein in its entirety. All publications referenced herein above are incorporated herein by reference in their entireties. Cited References:

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Claims

1. A system for three-dimensional object tracking, the system comprising

a first light source, comprising a plurality of infrared light emitters directed in mutually different directions covering at least a hundred and eighty degree angle range;

a first and second sensor at mutually different locations, configured to detect view angles from the first and second sensor to the first light source;

a calculation module configured to calculate from the view angles a distance from a baseline between the locations of the first and second sensor to the first light source.

2. A system according to claim 1, wherein the light emitters of said plurality are directed at successive angles in a three hundred and sixty degree angle range along a disk.

3. A system according to claim 2, wherein the disc comprises nine IRLEDs, covering emission over 360° in the plane of the disc and between 20°- 30° transverse to said plane.

4. A system according to claim 1 or 2, comprising a second light source and a light source carrier on which the first and second light source are mounted at a predetermined relative positions at mutually different heights, the calculation module being configured to calculate an orientation angle of a line between the light sources based on three dimensional coordinates of the first and second light source obtained using the first and second sensor.

5. A system according to claim 4, wherein the light source carrier is a head mountable device for use on a user's head, the first and second light source being mounted at mutually different heights above the head.

6. A system according to claim 5, wherein the head mountable device comprises a rod extending upwards from the position of the head, the first light source being mounted on said rod, at a position above the head.

7. A system according to claim 6, wherein said rod is an arched rod, extending in an arch over the head from positions on mutually opposite sides of the head.

8. A system according to claim 5, wherein the head mountable device comprises a head cap or a pair of glasses.

9. A system according to any one of the preceding claims, wherein the light emitting devices are infrared LEDs.

10. A system according to any one of the preceding claims, wherein the light sources comprise emitters configured to continuously send narrow band wavelength light.

11. A system according to claim 10, wherein the infrared light emitters are 940 nm infrared emitters.

12. A system according to any one of the preceding claims, comprising a platform with the first and second sensor mounted at stationary locations on a platform.

13. A system according to claim 12, wherein the platform is adjustable in height and has a moveable sensor holder that determines the angle of the first sensor relative to the baseline.

14. A system according to any one of the preceding claims, wherein the first and second sensor comprise infrared receivers, sensitive to infrared light.

15. A system according to any one of the preceding claims, wherein the first and second sensor are Nintendo WII remote controllers.

16. A head mountable device for use in an optical three dimensional head tracking system, the head mountable device comprising a first light source located at a first height above the head and comprising a disc with infrared light emitting devices configured to emit radiation directed in different directions covering at least a hundred and eighty degree angle range.

17. A head mountable device according to claim 16, wherein the light emitters of said plurality are directed at successive angles in a three hundred and sixty degree angle range along a disk.

18. A head mountable device according to claim 16 or 17, comprising a second light source located at a second height above the head and comprising a further disc with light emitting devices configured to emit radiation directed in different directions covering at least a hundred and eighty degree angle range;, the first and second height being mutually different.

19. A head mountable device according to claim 16, 17 or 18, comprising a rod extending upwards from the position of the head, the first light source being mounted on said rod, at a position above the head.

20. A head mountable device according to claim 19, wherein said rod is an arched rod, extending in an arch over the head from positions on mutually opposite sides of the head.

21. A head mountable device according to any one of claims 16-20, comprising a head cap or a pair of glasses.

22. A method of performing three-dimensional object tracking, using a first and second sensor located at opposite ends of a baseline to determine view angles to the object, the method comprising

emitting light from a first light source, comprising a disc with light emitting devices configured to emit radiation directed in different directions covering at least a hundred and eighty degree angle range;

- detecting view angles from the first and second sensor to the first light source;

calculating form said view angles a distance from the base line to the first light source.

23. A method according to claim 22, wherein the distance, D, is computed according to the formula

D=L*sin(alpha)*sing(beta)/sin(alpha+beta)

wherein L is the length of the base line and alpha and beta are the view angles from the first and second sensor to the first light source.

24. A method according to claim 22 or 23, comprising using a second light source comprising a further disc with light emitting devices configured to emit radiation over a 360 degree angle range, the first and second light source being located at a predetermined relative positions at mutually different heights.

25. A method according to claim 24, comprising calculating three dimensional coordinates of the first and second light source from view angles at which the first and second light source are visible from the first and second sensor and calculating an orientation of a line between the first and second light source from the three dimensional coordinates.