WO2002063456A1

WO2002063456A1 - Optical tracking computer interface

Info

Publication number: WO2002063456A1
Application number: PCT/AU2002/000125
Authority: WO
Inventors: Peter Lawrence Anderson
Original assignee: Anderson Technologies Pty Ltd
Priority date: 2001-02-08
Filing date: 2002-02-08
Publication date: 2002-08-15
Also published as: AUPR296601A0

Abstract

A system for tracking movement in order to provide information about the location of a body in space to a computing for processing. The system comprises a single video camera (1) located at a fixed viewpoint, a helmet (5) worn on the head of a user and a computing device (3) for obtaining three-dimensional position and orientation information by optically tracking the helmet (5), especially for the purpose of controlling a computer program. Visual output data generated by target software is provided to a transmitter (4) and sent using a frequency modulated radio signal to a receiver (8). The received visual output signals are provided to a display headset (8). The output data is displayed to the user providing a real time display, as generated by the target software application with which the user is interacting.

Description

OPTICAL TRACKING COMPUTER INTERFACE

FIELD OF THE INVENTION This invention relates to a system for tracking movement in order to provide information about the location of a body in space to a computer for processing. In particular, although not exclusively, the invention relates to a computer interface for obtaining three-dimensional position and orientation information by optically tracking the head of a user, especially for the purpose of controlling a computer program.

BACKGROUND TO THE INVENTION

Existing arrangements for human interfaces with computers include keypads, keyboards for dactyl serial input of predetermined characters or symbols, touch pads or drawing tablets for input of freehand lines or strokes using a finger or stylus, and pointing devices such as mice and trackballs for manipulation by a combination of fingers and palm of a user's hand. These arrangements are relatively unsuited to inputting position information, particularly if the user's hands are required for other tasks or the position information of interest is the user's head.

Applications that provide first person perspective views, such as flight simulators and some games especially require accurate position information of the head and resulting view. These applications are much more effective, with easier human interaction, if the view control is instinctive rather than contrived as in the control device examples above.

US Patent No. 5394517 (Kalawsky) describes an integrated real time display system which includes a sensor on a helmet mounted display for providing signals representing head movements to a computer system, especially in a virtual reality (VR) computer system such as used in flight simulators. However, this arrangement suffers from several disadvantages in that, to produce the required view of the cockpit, a purpose-built replica of the superstructure of the user's view must be available. An image of the inside of the cockpit must be captured by the head mounted camera, which precludes any relatively large head movements. The user must remain looking at the view template and is unsuited to applications where any view orientation is initiated by head movement.

US Patent No. 5694041 (Lescourret) describes a method for compensation of perturbations of magnetic field measurements made by a sensor, particularly in a system for determining the position and orientation of an aiming device mounted on a helmet.

US Patent No. 5841887 (Kuwayama et al.) describes an input device for a computer system wherein position and orientation is determined by a hand held input device. This is especially for manipulating a pointing image on a computer interface display. This input device interacts with an application on the computer system to produce change of position of a pointer on the screen in two dimensions (2D). The user's view is not manipulated in any other way and this manipulation is not reliant on head movements. The resulting view is from the third person perspective.

US Patent No. 6005548 (Latypov et al.) provides a useful discussion of other systems for tracking and displaying a user's body positions in motion, including mechanical systems, magnetic systems (also Lescourret above), ultrasonic systems and systems employing a plurality of optical fibres. However, the Latypov system suffers from magnetic interference and requires the calibration of more than 20 sensors for each person being tracked. Each sensor requires either a transmitter or cable for communication resulting in considerable infrastructure and associated expense. The system is not efficient in many applications, including any use where the users full body movements are irrelevant. This system gives accurate information about the orientation of various parts of the body which are relevant to full body movement analysis, but not to the orientation of the users view. The sensitivity of the device is not optimised for head movements.

The other systems discussed by Latypov suffer certain drawbacks, as follows. The mechanical systems are too slow to be effective in providing a realistic virtual reality experience. Ultrasonic systems are very fast but cost an enormous amount to configure and are also subject to interference. Fibre optic arrangements are very expensive and are not sufficiently sensitive to be practical in measuring small changes in the orientation of the head.

OBJECT OF THE INVENTION It is an object of the present invention to provide an optical tracking computer interface which ameliorates or overcomes at least some of the problems associated with the prior art.

It is another object of the invention to provide an optical tracking computer interface which is suited to virtual reality computer applications, but is relatively inexpensive to acquire and maintain.

It is yet another object of the invention to provide the public with a useful choice in relation to computer interfaces that track movement of bodies.

Further objects will be evident from the following description.

DISCLOSURE OF THE INVENTION

In one form, although it need not be the only or indeed the broadest form, the invention resides in an optical tracking interface for a computer including:

(a) a single optical image collection device located at a fixed viewpoint and producing image signals indicative of an image of a marker arrangement;

(b) the marker arrangement adapted to be worn by a computer user, movement of said marker arrangement relative to said fixed viewpoint enabling said single optical image collection device to determine positional information about the marker arrangement;

(c) a processor, coupled to the single optical image collection device, receiving the image signals and operative:

(i) to determine from said image signals the positional information about the marker arrangement, and (ii) to produce, in response to the positional information, instructions for the computer; and

(d) a visual display device coupled to the processor presenting to the user display data produced in response to the instructions. Preferably the marker arrangement is provided on an article of headgear, such as a helmet or cap.

Suitably the optical image collection device is a camera and desirably, in use, the marker arrangement is located in the camera's field of view.

Preferably the visual display device includes at least one screen placed in the visual field of the user.

Most preferably, the visual display device is adapted to be worn by the user, such as a headset or goggles, If required, both the marker arrangement and the visual display device may be carried by the article of headgear.

The marker arrangement may include a combination of contrasting coloured objects which, in use, provide images indicative of the pitch, roll and yaw of the user's head. The combination of contrasting coloured objects may comprise an outer surface of the article of headgear, a concentric spot provided on an upper surface of the headgear and a pointer object fixed in spaced relation to said headgear.

Alternatively, the combination of contrasting coloured objects may comprise an outer surface of the article of headgear and at least one stripe provided on an upper surface of the headgear.

Preferably, a first and a second stripe are provided on the upper surface of the headgear, the second stripe being substantially perpendicular to the first stripe. Preferably, the second stripe is shorter in length than the first stripe.

Most suitably the markers are provided on substantially spherical surface portions of objects comprising the marker arrangement.

Desirably the relationship between the headgear and the concentric spot is, in use, indicative of movement of the user's head in a substantially vertical plane. Desirably the relationship between the headgear and the pointer object is, in use, indicative of movement of the user's head in a substantially horizontal plane.

Desirably the relationship between the headgear and the at least one stripe is, in use, indicative of movement of the user's head in a substantially vertical plane.

Desirably the relationship between the headgear and the at least one stripe is, in use, indicative of movement of the user's head in a substantially horizontal plane. The processor is coupled to the optical image collection device and to the visual display device by a respective data transmission arrangement.

The data transmission arrangement may include a cable and/or a radio link, such as for carrying frequency modulated signals.

Suitably the processor is operative to determine positional information in the form of both the location and orientation of the marker arrangement.

Most preferably, the optical tracking interface allows a user to interact with a target computer program, which may be hosted either on the said processor or on an interconnected computer system.

In another form the invention resides in a method for determining the location and orientation of a computer user using a single optical image collection device located at a fixed viewpoint coupled to a computer, said method including the steps of: (1) providing a marker arrangement adapted to be worn by the computer user, movement of said marker arrangement relative to said fixed viewpoint enabling said single optical image collection device to determine positional information about the marker arrangement;

(2) collecting image signals indicative of an image of the marker arrangement produced by the optical image collection device;

(3) determining from said image signals, the positional information about the marker arrangement; (4) producing, in response to the positional information, instructions for the computer; and

(5) presenting to the user on a visual display device coupled to the computer, display data produced in response to the instructions. The step of providing the marker arrangement includes provision of a set of contrasting coloured objects, wherein the relationship between said objects is, in use, indicative of pitch, roll and yaw of the user's head.

Suitably the set of objects comprises an object having a substantially hemispherical portion of a first colour with a concentric spot of a second colour provided on a convex surface of the hemisphere, together with a spherical object of a third colour fixed in spaced relation with the said hemispherical portion.

Alternatively, the set of objects comprises an object having a substantially hemispherical portion of a first colour with at least one stripe of a second colour provided on the substantially hemispherical portion. Preferably, at least two stripes are provided with a first stripe being substantially perpendicular to a second stripe. Preferably, the first stripe is shorter in length than the second stripe.

BRIEF DETAILS OF THE DRAWINGS

To assist in understanding the invention preferred embodiments will now be described with reference to the following figures in which:

FIG. 1 is a schematic view of an optical tracking interface of a first embodiment; FIG. 2 is a block diagram illustrating components of the optical tracking interface;

FIG. 3A is a side elevational view of a first embodiment of the helmet; FIG. 3B is a top plan view of the helmet of FIG3A; FIG. 4A is the first portion of a flow diagram showing steps of a method for tracking objects in a three-dimensional space using the first embodiment of the helmet;

FIG. 4B is the second portion of the flow diagram showing the remaining steps of the method; FIG. 5 is a screen shot of an image showing a plan view of the second embodiment of the helmet and parameters used in the associated method;

FIG. 6A is the first portion of a flow diagram showing steps of a method for tracking objects in a three-dimensional space using the second embodiment of the helmet; and

FIG. 6B is the second portion of a flow diagram showing steps of a method for tracking objects in a three-dimensional space using the second embodiment of the helmet.

DETAILED DESCRIPTION OF THE DRAWINGS

In the drawings, like reference numerals refer to like parts. Referring to FIG 1 , an optical image collection device such as video camera 1 is arranged to scan a field of view. The camera 1 is suitably located above a user such that a wearable marker arrangement, associated with a helmet 5 worn on the head of the user, is in the field of view. A coloured background 7 with a high image contrast to the helmet 5 is provided for the camera's field of view. The camera 1 transfers data, in the form of image signals, from the scanning process via a cable 2 to a computing device 3.

The computing device 3 includes a processor that calculates from the image signals, in real time by way of a positioning program, positioning information about the marker arrangements associated with the helmet 5. This positioning information includes the actual three-dimensional location and orientation of the helmet 5 and thus the head of the user wearing the helmet. The computing device 3 also has a memory module 14 including RAM, and an input/output port 15 for coupling to other computer systems as required.

In the embodiment, the target application is also hosted on the computing device 3. Visual output data generated by the target software is provided to a transmitter 4 and sent using a frequency modulated radio signal to a receiver 8. The received visual output signals are provided to a visual display device, in the form of a display headset 8 provided on the helmet 5. The output data is then displayed to the user providing a real time display, as generated by the target software application with which the user is interacting. The electronic components of the interface of the embodiment are depicted in the block diagram of FIG. 2. The camera 1 is coupled via a cable 2 to a video capture card 9 located in the computing device 3. The video capture card 9 receives image signals from the camera 1 and digitizes the signals for input to a processor 10 in the computing device 3. The computing device hosts the positioning program 1 1 that calculates, in real time, the three-dimensional location and orientation of the marker arrangement associated with the helmet 5 of FIG. 1 , that is disposed in the image field of the camera 1. This is accomplished by processing the digital image data provided by the video capture card 9 to produce positioning information.

A first embodiment of the marker arrangement is illustrated in FIGS 3A and 3B of the drawings, which are schematic views of the helmet 5 and the associated passive markers. The outer upper hemispherical surface portion of the helmet shell 21 that is coloured white in the embodiment forms a primary marker of about 200mm in diameter. A black spot 22, of about 40mm in diameter, is provided concentrically on the outer upper hemispherical portion of the shell to form a secondary marker. A plan view of the helmet, as shown in FIG. 3B, will be that seen by the camera 1 when the helmet 5 is in the field of view. A tertiary marker, in the form of red coloured ball 23 of about

70mm in diameter, is fixedly supported by the helmet 5 such that its centre is about 300mm from the centre of the primary marker. The red ball 23 is spaced from the white shell 21 in the normal direction of viewing 24 by a wearer of the helmet. Thus the red ball 23 is sometimes referred to as a pointer object. The support member 25 for the red ball is arranged such that it is not detected by the positioning program and may, for example, also be coloured the same as the contrasting background 7 of FIG. 1.

The process of tracking user head movement by the positioning program 11 begins with light reflected by the helmet 5. This light is focussed by a lens of the video camera 1 onto an internal array of charge-coupled devices (CCDs). Outputs from this array are captured in grayscale and filtered within the camera to produce red-green-blue (RGB) values. These synthesized RGB values are sent to a video conversion unit, which sends corresponding video signals to the video capture card 9 via cable 2. The video system has an effective range of 400x400 pixels in the embodiment, which relates to the processing capability of the video capture card.

This card specification was chosen in the present embodiment as a suitable trade-off between cost, resolution and frame rate. The video capture card 9 passes digital image data representing the array to the processor 10 and memory 14 and across a data bus, such as a PCI bus. Once the data enters the processor/memory of the computing device 3, it is processed by a positioning algorithm developed by the applicant to determine the change of location and/or orientation of the marker arrangement and user's head.

The algorithm receives the data from each video frame captured as a digital array representing the RGB values at any given pixel location in the array. The steps of the algorithm 30 are now described with reference to the flow diagram illustrated in FIGS. 4A and 4B of the drawings. The array is scanned and filtered, by an initial step 31 of blanking out the background, to determine the location of the white object (ie. helmet shell 21 ). The area containing the white object is then found 32 by recognizing where the edges of the object occur as viewed from a notional horizontal (X-Y) plane. The white object is expected to have a size of about 50 pixels. If the white object is found 33, the identified area is expanded by a further 5 pixels in step 34. The new area used in a more thorough analysis of the white object area in step 35 to produce accurate object information. These accurate values include pixel area of the white helmet, which is statistically analyzed to determine the centre of the white object, labelled A in the algorithm. The location of the user's head, which is wearing the helmet 5, in the X-Y plane may then be determined.

Any changes in elevation and roll of the user's eye line are monitored by measuring the distance and direction that the black spot 22 on the white object 21 has moved from its concentric position. As the eye line is raised in a vertical (X-Z) plane, the black spot moves closer to the back edge of the white object. Conversely, as the user's head is moved to look down, the black spot moves closer to the front of the white helmet. The black spot is found by searching, in step 36, a white square region internal to the white object. The pixel area of the black object is then calculated in step 37 to provide minimum and maximum pixel area data.

The processing of this data about the black spot, labelled C in the flow diagram, produces the orientation of the user's head in the X-Z plane (ie. front-rear pitch). It will be appreciated that the image of the black spot 22 on the white spherical surface portion 21 of the helmet 5 will also reveal information about the orientation of the user's head in another vertical plane, namely the Y- Z plane (ie. left-right roll).

After the steps of blanking out both the white helmet 21 in step 38 and the black spot 22 in step 39, detection of a change of orientation of the helmet within a horizontal (X-Y) plane begins by locating the region containing the red pointer 23. Recognizing where the edges of a red object of approximately 10 pixels are, as viewed from the X-Y plane, provides a scan area. If the pointer is found 41 , a 5 pixel perimeter is added in step 42. The new area is more thoroughly analyzed in step 43 to produce accurate object pixel area information, labelled C.

The pixel area data A, B and C are then statistically analyzed in step 44 to determine the centres of the white, black and red objects. A line drawn through the centres of the white and red objects provides the orientation of the user's gaze within the horizontal plane, ie. line of sight yaw. The distance of the helmet 5 to the camera 1 along the Z axis can also be determined by pixel area in step 45. Thus pitch, roll and yaw information that is necessary for the computation of a view required to be presented to the user via the display 6 is obtained by the optical interface. The three-dimensional resultant co-ordinates describing the user's head location and orientation can be interfaced with an existing target application, once the mechanisms of data input for that application are known and understood. In one arrangement, the application processes the coordinate information as from a standard input device and produces the resulting view for video output. The user views the updated image in the headset video output resulting in a real-time simulation of the users actual direction of view within the target 3D application. A second embodiment of the passive marker arrangement that may be utilised is illustrated in FIG. 5 of the drawings, which is a screen shot showing a plan view image of the helmet 5 on the visual display device, as seen by the camera 1 , after processing by the image processing software of the invention. The outer upper hemispherical surface portion of the helmet shell 21 that is coloured white in the embodiment forms a primary marker of about 300mm in diameter. A first black stripe 100, of a width of about 20mm, is provided on and bisects the outer upper hemispherical portion of the shell to form a secondary marker. A tertiary marker in the form of a second black stripe 101 , of a width of about 20mm and a length of about 100mm, is also provided on the outer upper hemispherical portion of the shell and lies substantially perpendicular to the first black stripe 100.

With the second embodiment, the user's yaw movement, or location in the X-Y plane is determined from the secondary marker 100. The first black line 100 extends over the outer upper hemispherical portion such that the first black line 100 remains visible to the camera 1 despite any changes in elevation or roll of the user's eye line. One end of the first black line 100 is effectively marked red, and the other end of the first black line is effectively marked green, by the image processing software to keep track of the direction in which the user is looking.

Any changes in elevation of the user's eye line are monitored by measuring the distance that the second black line 101 effectively moves along the first black line 100. For example, with reference to FIG. 5, the left hand end of the first black line 100 may be "marked" red by the image processing software, with the red end representing the direction in which the user is looking. The right hand end of the first black line 100 may be "marked" green. If the user moves their head down, the second black line 101 will move closer to the red end of the first black line. Conversely, if the user raises their head, the second black line will move closer to the green end of the first black line 100. The second black line 101 provides a sharp contrast in the thickness and therefore pixel count along the first black line, thus enabling the orientation of the user's head in the X-Z plane (i.e. front-rear pitch or inclination) to be accurately determined.

The image of the second black line on the white hemispherical surface portion 21 (i.e. the primary marker) of the helmet 5 will reveal information about the orientation of the user's head in the Y-Z plane (i.e. left- right roll).

Since the second embodiment does not comprise the red ball 23 of the first embodiment, a smaller area needs to be scanned, which reduces the required processing time. A greater range of user head inclination and roll is also possible because there is no longer the requirement of the head tracking software to cater for object eclipse.

Tracking user head movement using the second embodiment of the marker arrangement utilizes a different algorithm 50 from the algorithm 30 used with the first embodiment. The algorithm 50 and processing for the second embodiment will now be described with reference to the image of the second embodiment of the helmet 5 shown in FIG. 5 and the flow chart of the method shown in FIGS. 6A and 6B.

The following pieces of information are attempted to be determined from each video image's RGB pixel data: the pixel co-ordinates of the centre of the white helmet 5, helmet 5 being referred to as objectA; the pixel area of the helmet 5; the pixel co-ordinates of the centre of one particular end of the first black line 100, which bisects the helmet 5 and which will be referred to as objectB; the pixel co-ordinates of the centre of the opposite end, relative to objectB, first black line 100, which will be referred to as objectC; and the pixel co-ordinates of the centre of the second black line 101 will be referred to as objectD.

Using the above properties of the image, the values for X,Y,Z, yaw, pitch and roll of the helmet 5 can be determined by using geometrical calculations and constants. For algorithm 50, the following are assumed: helmet 5 is the only significant white object in the field of view of the video camera 1 ; when this algorithm initializes, one end, for example, objectB, of first black line 100 lies closer to pixel co-ordinates (0,0) and the opposite end point, objectC, lies closer to pixel co-ordinates (640,480); the previous image, (i.e. the video image priorto the current video image), has been processed and objectA, objectB, objectC and objectD have been successfully recognized; helmet 5 can only move a maximum distance of, for example, 5 pixels in any direction in approximately 30msec; the yaw of helmet 5 can only change a maximum of about 60 degrees in approximately 30msec; and, 32 bit RGB pixel data is received from the video camera 1 in this algorithm. However, any type of digital representation is acceptable.

In the following description of algorithm 50, the terms video image, video frame and video buffer all refer to 32 bit RGB pixel data representing a visual image captured by the camera 1 at a particular point in time. The term "reasonable" means that the values used are based on the known pixel area and pixel dimensions of a particular object. The object's physical size, distance from the video camera, the video camera's field of view, ambient lighting and the maximum distance that the object can physically move in between video frames determine the required values. The term "successfully recognized" means that the object was successfully measured in terms of its X and Y pixel coordinates and that the measured pixel area P of the object, lies within reasonable boundaries. All objects are represented in terms of their object (X,Y,P) recognized value. The term "successfully processed" means that objectA(x,y,p), objectB(x,y,p), objectC(x,y,p), objectD(x,y,p) were all successfully recognized in the video image. All measurements are in terms of pixels unless stated otherwise.

The steps of the algorithm 50 are now described with reference to the flow diagram illustrated in FIGS. 6A and 6B of the drawings and the image shown in FIG. 5.

In step 52, the global variables for objectA, objectB, objectC, and objectD are initialized. In step 54, a global Boolean variable is set to FALSE regarding whether or not the previous video image was successfully recognized. The processing shown in steps 56-64 is then performed for every video frame received from the video camera. With reference to step 56, if the helmet 5 was not found in the previous video image, steps 58-64 are followed. If the pixel area of objectA is not reasonable then processing is terminated for this video frame. At step 56, if the previous video image was successfully recognized, the algorithm 50 proceeds to the steps shown in FIG 6B.

With reference to the image shown in FIG 5 and FIG 6B, based on objectA, the MaxRadius, defined as the maximum reasonable distance from the centre of objectA is calculated, as shown in step 68. Typically this value is 5 pixels greater than the pixel radius determined from objectA. The EdgeRadius is then calculated in step 70 and is defined as the maximum reasonable distance from the centre of objectA and which identifies the edge of objectA. The

InnerRadius is calculated in step 72 and is defined as the maximum reasonable distance from the centre of objectA, which identifies the internal non-edge pixels of objectA. Non-edge pixels refer to those pixels that do not represent the edge of ObjectA.

The intercept c and gradient m for the line y=mx+c that passes from objectB(x,y,p) through objectC(x,y,p) is then calculated, as shown in step 74. A value C is then calculated represented by step 76 in FIG. 7B. C specifies a band that is within a reasonable pixel distance, for example 45 pixels, perpendicular to the line that joins objectB(x,y,p) to objectC(x,y,p), i.e. a band of width C perpendicular to the line that joins objectB(x,y,p) to objectC(x,y,p). A value C1 , equal to c-C, is then determined in step 78 and a value C2, equal to c+C, is determined in step 80. In step 82, all the pixel data from the current video image that does not lie within the MaxRadius distance from the recognized centre of objectA is removed.

With reference to FIG. 5, the data sets A-J are created based on the video image's remaining pixel data, as represented by step 84. The contents of the data sets A-J are as follows:

SetA: The set of all pixels whose distance from the centre of objectA lies between 0 and the InnerRadius;

SetB: The set of all pixels whose distance from the centre of objectA lies between the InnerRadius and the EdgeRadius; SetC: The set of all pixels whose distance from the centre of objectA lies between the EdgeRadius and the MaxRadius;

SetD: The statistical analysis of all "non-white" pixels in setAthat are selected by the RGB filter of (R<225 or G<225 or B<255) followed by the generation of a new objectD(x,y,p);

SetE: All pixels in setB that do not satisfy the relationship C1 <c<C2, which is mutually exclusive from setF;

SetF: All pixels in setB that satisfy the relationship C1<c<C2; SetG: All "white" pixels that are selected by the RGB filter of

(R>225 or G>225 or B>225);

SetH: All "white" pixels that are not selected by the RGB filter of (R>225 or G>225 or B>225), thus mutually exclusive from setG;

Setl: All the pixels in setl that are closer to the current objectB(x,y,p) than current objectC(x,y,p); and

SetJ: All the pixels in setJ that are closer to the current objectC(x,y,p) than current objectB(x,y,p), thus mutually exclusive from setl.

To track user head movement, data is calculated from the above data sets, as shown in steps 86-90 in FIG. 6B. The processes represented by step 86 are as follows: statistically analyse setAU setB U setC to generate a new objectA(x,y,p); statistically analyse setl to generate a new objectB(x,y,p); statistically analyse setJ to generate a new objectC(x,y,p).

Using objectA(x,y,p), objectB(x,y,p), objectC(x,y,p) and objectD(x,y,p), derived from step 84, the known geometric properties of the helmet 5 and by using simple geometrical rules, calculations and constants familiar to one skilled in the art, the values for X, Y, Z, yaw, pitch and roll of the helmet 5 can be computed, as represented by step 88. In step 90, the global Boolean variable that determines whether the previous video image was successfully recognized is set to TRUE. It will be appreciated that the present invention is not limited to the type of marker arrangement used and numerous variations on, for example, the second embodiment of the passive marker arrangement are envisaged. As an alternative to the substantially perpendicular lines 100 and 101 , three circular markers arranged in a triangular formation could be used. Persons skilled in the relevant art will recognize changes to the method described for the second embodiment that would need to be made to determine the positional information from the triangular marker arrangement. The object tracking system, in this form of the invention, runs on the MS Windows 98 operating system and is configured as a standard windows application which accesses the video data using the standard windows video capture application programming interface. The Genesis 3D application program is a shareware 3D modelling and visualisation tool and is used as the environment in which to test the object tracking system.

The positioning information is converted to a form suitable for input to a target application program 12 that is also hosted on the processor 10 in the embodiment. The target application may be a first person perspective adventure/action game or a virtual floor plan viewer. Visual outputs from the target application program 12 are provided to a video card 13, which generates video driver signals for a video display. The video driver signals may be provided directly to a conventional display device. In the embodiment however, the driver signals are provided to a radio transmitter 4, which transmits an FM encoded radio signal to a radio receiver 8.

As shown in FIG. 2, the radio receiver 8 is associated with the helmet 5 and feeds the video driver signals to a display device, suitably a visual display headset 6, mounted on the user's helmet 5. This arrangement allows a user wearing the helmet to interact in substantially real time, via the optical tracking interface, with the target application program 12. The user's head movements are converted into inputs for the target program and display outputs generated in response to those inputs are provided to the display device for presentation to the user.

In other embodiments, the optical image collection device may include a digital camera with direct conversion to digital pixel data; the data transmitter and receiver arrangement may include an infra-red link or other suitable near-field arrangement; the visual display device may include a cathode ray tube (CRT), liquid crystal, thin film transistor (TFT) or other display screens.

Similarly, the markers may be adapted for wearing on other body parts or appendages for use in, for example, studies of human movements. The target software application may be hosted on another computer system that communicates with the interface processor, if required. The optical image collection device may be positioned at any suitable location relative to the user. Throughout this specification, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features or sequence of method steps.

Claims

1. An optical tracking interface for a computer including:

(c) a processor, coupled to the single optical image collection device, receiving the image signals and operative: i. to determine from said image signals the positional information about the marker arrangement, and ii. to produce, in response to the positional information, instructions for the computer; and

(d) a visual display device coupled to the processor presenting to the user display data produced in response to the instructions.

2. The optical tracking interface of claim 1 , wherein the marker arrangement is provided on an article of headgear.

3. The optical tracking interface of claim 1 , wherein the optical image collection device is a camera and in use, the marker arrangement is located in the camera's field of view.

4. The optical tracking interface of claim 1 , wherein the visual display device includes at least one screen placed in the visual field of the user.

5. The optical tracking interface of claim 1 , wherein the visual display device is adapted to be worn by the user.

6. The optical tracking interface of claim 2, wherein both the marker arrangement and the visual display device are carried by the article of headgear.

7. The optical tracking interface of claim 1 , wherein the marker arrangement includes a combination of contrasting coloured objects which, in use, provide images indicative of the pitch, roll and yaw of the user's head.

8. The optical tracking interface of claim 7, wherein the combination of contrasting coloured objects comprise an outer surface of the article of headgear, a concentric spot provided on an upper surface of the headgear and a pointer object fixed in spaced relation to said headgear.

9. The optical tracking interface of claim 7, wherein the combination of contrasting coloured objects comprise an outer surface of the article of headgear and at least one stripe provided on an upper surface of the headgear.

10. The optical tracking interface of claim 9, wherein a first and a second stripe is provided on the upper surface of the headgear, the second stripe being substantially perpendicular to the first stripe.

1 1.The optical tracking interface of claim 10, wherein the second stripe is shorter in length than the first stripe.

12. The optical tracking interface of claim 1 , wherein markers are provided on substantially spherical surface portions of objects comprising the marker arrangement.

13. The optical tracking interface of claim 8, wherein the relationship between the headgear and the concentric spot is, in use, indicative of movement of the user's head in a substantially vertical plane.

14. The optical tracking interface of claim 8, wherein the relationship between the headgear and the pointer object is, in use, indicative of movement of the user's head in a substantially horizontal plane.

15. The optical tracking interface of claim 9, wherein the relationship between the headgear and the at least one stripe is, in use, indicative of movement of the user's head in a substantially vertical plane.

16. The optical tracking interface of claim 9, wherein the relationship between the headgear and the at least one stripe is, in use, indicative of movement of the user's head in a substantially horizontal plane.

17. The optical tracking interface of claim 1 , wherein the processor is coupled to the optical image collection device and to the visual display device by a respective data transmission arrangement.

18. The optical tracking interface of claim 17, wherein the data transmission arrangement includes a cable and/or a radio link.

19. The optical tracking interface of claim 18, wherein the cable and/or radio link is for carrying frequency-modulated signals.

20. The optical tracking interface of claim 1 , wherein the processor is operative to determine positional information in the form of both the location and orientation of the marker arrangement.

21.The optical tracking interface of claim 1 , which allows a user to interact with a target computer program, the target computer program being hosted either on the said processor or on an interconnected computer system.

22. A method for determining the location and orientation of a computer user using a single optical image collection device located at a fixed viewpoint coupled to a computer, said method including the steps of:

(a) providing a marker arrangement adapted to be worn by the computer user, movement of said marker arrangement relative to said fixed viewpoint enabling said single optical image collection device to determine positional information about the marker arrangement;

(b) collecting image signals indicative of an image of the marker arrangement produced by the single optical image collection device;

(c) determining from said image signals, the positional information about the marker arrangement;

(d) producing, in response to the positional information, instructions for the computer; and

(e) presenting to the user on a visual display device coupled to the computer, display data produced in response to the instructions.

23. The method of claim 22, wherein the step of providing the marker arrangement includes provision of a set of contrasting coloured objects, wherein the relationship between said objects is, in use, indicative of pitch, roll and yaw of the user's head.

24. The method of claim 23, wherein the set of contrasting coloured objects comprises an object having a substantially hemispherical portion of a first colour with a concentric spot of a second colour provided on a convex surface of the hemisphere, together with a spherical object of a third colour fixed in spaced relation with the said hemispherical portion.

25. The method of claim 23, wherein the set of contrasting coloured objects comprises an object having a substantially hemispherical portion of a first colour with at least one stripe of a second colour provided on the substantially hemispherical portion.

26. The method of claim 25, wherein at least two stripes are provided with a first stripe being substantially perpendicular to a second stripe.

27. The method of claim 26, wherein the second stripe is shorter in length than the first stripe.