FIELD OF THE INVENTION

A motion tracking system is described that finds use in linking motion on a locomotion platform to visual software viewed by a user using the locomotion platform.

BACKGROUND TO THE INVENTION

Locomotion platforms provide a means of single-, multi- or omni-direction movement exemplified by ambulation or simulated walking e.g. using a reciprocating foot sliding motion, whilst maintaining the user in a fixed location that is within the bounds of the locomotion platform. We have described a locomotion platform in our earlier patent US7,470,218.

Locomotion platforms and directional treadmills find application in enhancing virtual world immersion where users are provided with typically a large format screen display or head mounted display providing visual immersion, and the locomotion platform enables "movement" in the imaged virtual world. Profound virtual reality immersion is brought about by visual content, sound and movement, the latter giving rise to proprioceptive and kinaesthetic familiarity and memories, giving rise to better immersion.

Ideally when a user moves their feet on a locomotion platform to "walk" or "run" in a virtual world presented to them by a screen or head mounted display, the visual scene should move and modify as expected as if the user was actually present in the virtual world scene. Indeed synchronisation between user movement in the real world and their first person view in a virtual world is important for profound immersion. Lack of synchronisation is called latency and brings about a "break in presence" i.e. the user's mind is brought back to the present reality. Motion tracking and synchronisation of this motion between real and virtual worlds is thus important for profound virtual reality immersion. Motion tracking on locomotion platforms has taken a variety of different forms depending on the method of locomotion and accessibility of the user. For instance roller style treadmills can provide roller movement and so information on initiation, duration and stopping of movement by way of suitable sensors attached to the rollers. This information can be linked to visual software to provide synchronised movement in a virtual world. The Virtusphere™, a large "hamster ball" on pairs of orthogonally mounted rollers enables a user inside the sphere to walk around using a wireless head mounted display, with motion being captured from the rollers and synchronised with the visual scene presented to the user.

However roller locomotion platforms have not found wide success because of size, complexity and system inertia. No direct access to the user means wireless head tracking needs to be synchronised with roller movement, and challenges with system inertia plus cost of wireless head tracking have limited uptake of this technology.

Alternative approaches use optical tracking, particularly using time-of-flight or projected patterns to determine an object's position and motion; such approaches may be termed remote sensing. Xbox Kinect™, Xbox One™ and the Eye Toy™ are examples of this technology. Optical tracking typically uses dual cameras and algorithms to determine the position and movement of objects and can successfully link virtual and real world motion. However this technology is costly and complex for end users and for many users requires too large an area e.g. of home or office for optimal use of the cameras. Optical remote sensing also requires visual access to the user to identify the walking motion, and this presents a problem to locomotion platforms which often have support structures which limit a line of sight to the user.

In our earlier patent US7,470,218, the entirety of which is incorporated here by reference, there are described other approaches to motion tracking as follows: In one mode of use, the user wears virtual reality visual display glasses and wears 3- dimensional tracking devices on or close to their feet. 3-dimensional tracking devices are typically used for motion capture. These devices output channels of information that corresponds to their X, Y and Z position relative to a magnetic 'source'. A computer program that samples the X, Y, and Z positions at sufficiently short intervals can compute the user's speed and direction. In another mode of use, the platform upper surface contains a plurality of pressure sensors. These are activated as the user's feet press upon them. By analysing the position and sequence of activated sensors, relative to time, the user's speed and direction is computed.

The magnetic and pressure based motion tracking examples referenced above are effective but these motion tracking solutions are complex and carry significant cost. To address current problems of motion tracking on locomotion platforms i.e. complexity, associated cost, limited application and challenging implementation, aspects of the present invention seek to provide a simple, low cost, generally applicable motion tracking solution based on audio tracking that, in embodiments, is able to use audio hardware and software accessible on most computers.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a motion tracking means/system for a locomotion platform comprising a locomotion platform, at least one acoustic detection device, footware worn by a user using said locomotion platform and at least one means of interpreting signal from said at least one acoustic detection device said interpretation influencing visual software driven by computer type hardware and imaged by at least one imaging device.

Preferably there is provided footware that generates sound when sliding on the locomotion platform.

Usefully footware is provided wherein footware interface surface or sole differs between feet and generates a different sound from each foot when sliding on the locomotion platform.

In one embodiment a locomotion platform is provided wherein at least one acoustic detection device is close to, attached mechanically, adhesively or moulded to a surface of the locomotion platform. In a preferred embodiment there is a means of tracking motion wherein the locomotion platform is a single moulded piece and is substantially dish shaped.

In various formats there is provided a substantially dish shaped locomotion platform made from a polymer said polymer exemplified by the following engineering polymers: PTFE, PET, ABS, HDPE (high density polyethylene), UHMWPE (ultra-high molecular weight polyethylene), PA6, PA66. Other polymers and polymer combinations are possible. Usefully a substantially dish shaped locomotion platform is provided wherein said dish comprises one or more formed sections wherein forming is exemplified by thermoforming or injection moulding.

In one embodiment there is provided a motion tracking means wherein output from the at least one acoustic detection device provides motion control signal in accordance with those recognised by computer driven by 2D or 3D visual software to achieve locomotion displayed by the at least one imaging device.

Usefully at least one imaging device is provided wherein said imaging device is emitting or projection screen technology for one or more viewers or head mounted display for an individual viewer or both.

Preferably there is provided a motion tracking means wherein signal from the acoustic detection device is (amplified and) interpreted by computer microphone audio card and associated software.

Preferably a motion tracking means is provided wherein at least two acoustic detection devices are mounted on or close to a surface of the locomotion platform. Advantageously there is provide a motion tracking means wherein at least one of the at least two acoustic detection devices is used for noise cancellation to attenuate or remove sound generated by motion of footwear on the locomotion platform.

In another embodiment a motion tracking means is provided wherein said at least two acoustic detection devices provide signal data input to said computer driven 2D or 3D visual software providing locomotion and direction of motion translation between said locomotion platform and said visual software outputted to one or more screens.

Valuably the top surface of a dish shaped locomotion platform is provided with positive or negative embossments, embossed in the dish surface.

Preferably a dish shaped locomotion platform engages or interacts with footware such that the footware produces sound patterns when sliding on the embossed patterns. In another aspect of the invention there is provide a motion tracking means comprising a dish shaped locomotion platform, footware and embossed patterns and at least one acoustic detection device wherein said embossed patterns are different in different regions of said dish producing different sound patterns when said footware slides across said different regions, said different sound patterns enabling feet location and direction to be interpreted by way of said means of interpreting signal from said at least one acoustic device said interpretation influencing visual software driven by a computer type hardware and imaged by at least one imaging device.

In a further aspect the invention provides a simulated-environment motion tracking system, comprising: a locomotion platform on which a user is able to simulate locomotion by sliding the user's feet back and forth over a surface of the platform; at least one acoustic sensor acoustically coupled to the platform to detect an acoustic signal from the sliding of the user's feet; and a signal processor, coupled to said acoustic sensor, to process a signal from said acoustic sensor and, in response, output a motion detect signal, said motion detect signal indicating when said user is simulating locomotion.

In embodiments the acoustic sensor (acoustic detection device) comprises a microphone, piezoelectric sensor or the like, and detects an acoustic signal from interaction between footwear worn by the user and the surface of the platform. For example, in embodiments the sensor may be attached beneath one edge of the platform. When a user is simulating locomotion typically the user slides their feet alternately back and forth over the surface of the platform which, in embodiments, has the form of a shallow dish so that the user remains in a generally central position. Thus the leg motion of the user does not correspond precisely to either normal walking or running leg motion since in general the user's feet remain in contact with the platform at substantially all times. However experiments by the inventors have established that where the user is presented with an appropriate visual stimulus the brain of the user creates a strong impression of actual walking (or running) without the need for the user to completely remove a foot from the platform. Attempting to walk normally can be relatively tiring.

In some preferred implementations, therefore, the system is coupled to a display device to control display of a computer-based simulated environment in response to detection of the user's simulated locomotion. More particularly the simulated environment may be controlled to provide visual cues corresponding to the user walking or running in the environment. In embodiments such visual cues may comprise undulation of the simulated environment, for example in a generally vertical direction. To simulate walking the undulation is small; for running the undulation is larger. The motion detect signal provided by the motion tracking system may provide information relating to when the user is moving one or other of their feet; optionally this may be used to synchronise this undulation. However in practice good results have been obtained simply using a motion detect signal to indicate when the user is simulating locomotion (as opposed to remaining substantially stationary), without needing to provide more detailed information.

In embodiments the acoustic signal detected by the sensor changes as a user's foot is moved across the platform - the signal begins at a low level, for example around zero, when the foot is stationary, increases to a maximum as the foot slides across the platform, and again reduces to a low level, typically substantially zero, as the foot once again comes to a halt. It has been found in practice that both the maximum amplitude of the signal and the duration of the envelope correlate with the speed of simulated locomotion. Either signal amplitude or envelope duration may be employed as a measure of rate of locomotion (duration inversely correlating with rate), but the best results are obtained by combining both types of information: Slow simulated walking results in a long envelope duration of relatively low amplitude; and vice versa. The skilled person will appreciate that there are many ways in which amplitude may be taken into account including, for example, determining a maximum or average amplitude over the duration of a 'stride'. Preferred embodiments of the system therefore provide a motion detect signal which indicates a rate of the simulated locomotion. In one embodiment the motion detect signal comprises a signal which repeats at a rate which is dependent on the detected rate of simulated locomotion. In embodiments the system may also provide a motion detect signal which indicates a direction of the simulated locomotion of the user. This is particularly advantageous in a virtual reality (VR) or similar system in which user gaze tracking is employed (for example by tracking motion of a head-mounted display). This is because this enables user movement in the environment to be disassociated from gaze direction in the environment - i.e. the user is not required to move in the direction in which they are looking. We describe below some techniques which may be employed to determine simulated motion direction; these may be used separately or in combination.

In one approach two (or more) acoustic sensors are acoustically coupled to the platform at different locations and the signal processing combines signals from the two sensors to establish a direction of user simulated locomotion. The direction of simulated locomotion may correspond to a direction in which the user is facing on the locomotion platform. In embodiments the signals from the two sensors are used to triangulate positions of the user's feet (with an ambiguity as to which foot is which). The skilled person will appreciate that the use of two or more sensors, for example with triangulation, is not restricted to locomotion direction sensing but may be employed, for example, to provide information, or additional information, on the rate of simulated locomotion and/or information on foot locations. In embodiments the use of just two acoustic sensors facilitates interfacing to a stereo audio input of a computer, for example a computer displaying a simulated environment. In embodiments the sensors are around 90° apart; thus in embodiments the acoustic sensors subtend an angle (about an axis aligned with a vertical axis of the user) of between 45° and 135°.

Where multiple acoustic sensors are employed, additionally or alternatively to triangulation more sophisticated signal processing may be used. In one approach a model of the user's simulated locomotion (foot movement) is used to model the sounds expected from the acoustic sensors. Then the model may be adjusted by adjusting, for example, one or both of the user's rate and direction of simulated locomotion, to match simulated acoustic data with the observed acoustic data.

In another approach the surface of the locomotion platform is configured such that different acoustic signals are produced by different regions of the surface. In broad terms, therefore, one or more characteristics of a detected acoustic signal map to one or more regions of the surface of the platform, and this may be used to locate the user's feet. In practice, as described further below, it is not necessary to employ a sophisticated mapping of signal characteristics to location to obtain useful information, such as motion rate/direction, from an approach of this type.

In some preferred embodiments the surface of the platform has an embossed or relief pattern, with raised and sunken portions. Typically the surface of the platform comprises a polymer such as polyethylene (preferably with a low surface energy, for low friction). The embossed pattern may be a moulded pattern, for example a pin-seal pattern. The pattern may be random, quasi random, or substantially regular. In embodiments the platform is gently dished.

In preferred embodiments the user is provided with footwear such as a pair of shoes or the like. The soles of the shoes are preferably then provided with a plurality of pads, preferably of a hard material such as ceramic to provide a low friction interface. When such a shoe slides over the platform surface the pads interact with the raised portions of the embossed pattern to generate an acoustic signal. This signal, whilst comprising a range of frequencies, may have a characteristic frequency dependent on one or more of: a spatial frequency of the raised portion of the embossed pattern, a number or spatial frequency of the pads on the shoes, and the rate of motion of a shoe over the platform surface. In embodiments typically between 20 and 100 pads are employed on a sole. Such an approach may be used to generate characteristic frequencies for example in the range 0.1 KHz to 20KHz.

As the skilled person will appreciate, the parameters of the system may be adjusted to adjust the characteristic frequency, for example taking into account the frequency response of the acoustic sensor. Additionally or alternatively the embossed pattern may be employed to modify the acoustic signals in other ways, for example by changing the shape of the relief pattern. Example profiles of the raised portions of the pattern may include, but are not limited to: a smooth, continuous curve; a discontinuous line with one or more steps; square, rectangular, triangular, sawtooth and domed profiles; and the like.

In some preferred embodiments the embossed pattern varies over the surface of the platform such that the acoustic signal, more particularly a characteristic frequency of the acoustic signal, varies with the location of a user's foot. In one example pattern the platform is (radially) segmented and different (radial) segments of the surface of the platform have different embossed patterns. In broad terms, in some preferred patterns the proportion of different frequencies detected by an acoustic sensor changes as the foot of a user slides across the surface. Then the signal processing may respond to this proportion to identify the location of one or both feet (although typically with an ambiguity as to which foot is which). Such signal processing may additionally or alternatively be used, for example, to determine the relative position of one foot with respect to the other. Again the skilled person will appreciate that such an approach could be used to determine rate and/or direction of the user's simulated locomotion, or other information relating to position and/or movement of the user's feet.

As previously described, in some preferred embodiments the motion tracking system is coupled to a computer display system to control display of a computer-based simulated environment to the user, in response to the detected motion. Thus in this case the motion detect signal may be a motion control signal. For example the signal may comprise a 'go forward' signal for a character in a computer game. Optionally the motion tracking signal may provide a walk/run output signal to such game or other software, based upon a detected rate of simulated locomotion. The simulated environment may be a virtual reality environment employing immersive display technology, such as a head-mounted display, or the display may be a display of a 2D or 3D simulated environment, for example of the type commonly employed in computer games.

Some unwanted noise may be generated by the user's simulated locomotion on the platform. In embodiments this may be detected, for example by the at least one acoustic sensor or by a separate sensor, and then this signal provided to a noise cancellation system to attenuate unwanted acoustic noise resulting from use of the device. Such a noise cancellation system may employ a separate speaker or may employ the platform itself as an acoustic transducer for noise cancellation. Such noise cancellation can be particularly effective because of the relatively uniform sound generated by use of the system.

In a related aspect the invention provides a method of motion tracking for a simulated environment using a motion tracking system as described above, in particular by processing the signal from at least one acoustic sensor acoustically coupled to a locomotion platform to detect sliding of the user's feet over the platform surface, to thereby determine when/whether the user is simulating locomotion. Optionally such a method may further determine one or more of a rate of simulated locomotion and a direction of simulated locomotion. The invention further provides a signal processor as described above, which may comprise a suitably programmed general purpose computer system, games machine, or the like. Such a signal processor is configured to process a signal from an acoustic sensor coupled to a locomotion platform, to determine and output a motion detect signal indicating when the user is simulating locomotion by sliding feet back and forth over a surface of the locomotion platform.

In embodiments such a signal processor comprises an audio input to receive a signal from the one or more acoustic sensors; and a processor coupled to the input, and to working memory and non-volatile program memory storing processor control code for performing the signal processing. Such code may be provided on a non-transitory data carrier such as a disc or programmed memory. The code (and/or data) may comprise source, object or executable code in any conventional programming language, and may be distributed between a plurality of coupled components in communication with one another. The signal processing may alternatively be implemented on a digital signal processor (DSP) and/or using dedicated hardware.

The skilled person will appreciate that features from aspects and embodiments of the invention described above may be combined. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be further described, by way of example only, with reference to the following drawings in which:

Figure 1 shows a perspective schematic diagram of a user on a locomotion platform;

Figure 2 shows a block diagram of a motion tracking means; Figures 3 and 3a show, respectively, a schematic drawing of locomotion platform footware, and a schematic diagram of a low friction footware disc;

Figure 4 shows a schematic drawing of a locomotion platform with attached acoustic detection devices;

Figures 5a and 5b show, respectively a schematic drawing of negative embossments, and is a schematic drawing of positive embossments;

Figure 6 shows a schematic drawing of multiple different region embossed locomotion platform; and

Figure 7 shows a schematic drawing of the interaction of the sole of a shoe bearing pads with a relief pattern on the surface of a locomotion platform, indicating the generation of sound having a characteristic frequency.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Figure 1 there is provided a concave platform 10 for a user 15 to stand on. Platform 10 has surface 200 and together with user's footwear 90 comprise materials to reduce interface friction. Further objectives are that the user 15 remains substantially constrained to the platform 10 area and that user 15 may turn and walk in any horizontal direction. Continuing to refer to Figure 1 , in which locomotion platform 10 is shown schematically, user 15 slides their feet in more or less of a reciprocating action wearing footware 90 in contact with a top surface 200 of a locomotion platform 10 to which acoustic sensors 20 have been attached. Acoustic sensors 20 are preferably attached to bottom surface 230 of the locomotion platform 10 or indeed the side 210, so long as the position of acoustic sensor enables pick-up of vibrations generated by motion of the user's 15 feet and footware 90 and does not interfere with the sliding action of the user's footware 90. In a preferred embodiment and with reference to Figure 4, acoustic detection devices 20 are mounted on the bottom surface 230 of locomotion platform 10. In embodiments the platform forms a cavity 3 when in use on a floor or base 28 (Figure 4).

With reference to Figure 2, there is provided a motion tracking means 5 for a locomotion platform 10 comprising a locomotion platform 10, at least one acoustic detection device 20, footware 90 worn by a user 15 using said locomotion platform 10 and at least one means 35 of interpreting signal from said at least one acoustic detection device 20, said means 35 of interpreting signal providing influence of visual software driven by computer type hardware 40 and imaged by at least one imaging device 60, 80. With reference to Figures 1 and 3 which illustrate means for motion tracking, there is provided footware 90 worn by a user 15 that generates sound or vibrations when sliding on said locomotion platform 10. Sound may be generated by any interaction of surfaces 440, 200. The skilled person will recognise that a wide range of types of such surfaces may be employed, although preferably they also function to reduce friction between said interacting surfaces. Exemplar surfaces are ceramic and polymer where for convenience ceramic is likely to be associated with footware 90 and polymer with that of locomotion platform 10, though the reverse combination is included: Examples of possible surface combinations include: polymer / polymer, metal / polymer, glass / polymer. A useful combination is alumina discs 460 and high density polyethylene for locomotion platform 10. Though a disc 460 is shown in Figure 3 and 3a, this is for illustration purposes only and any shape may be used so long as interaction surface 440 exhibits low friction (coefficient of friction <0.2) with locomotion platform surface 200. With reference to Figure 4 there is provided a locomotion platform 10 wherein said at least one acoustic detection device 20a,b,c,d,e is close to, attached mechanically, adhesively or moulded to surface 200, 230, 215, 210 of said locomotion platform 10. With reference to the polymer that substantially forms the locomotion platform 10, there is a preference for using a polymer of elasticity modulus between 500MPa to 3GPa so as to minimise harsh noise and yet transport sound generated by interacting surfaces 440 and e.g. 200 to acoustic detection device 20. Vibrations caused by motion of footware 90 on a polymer locomotion platform 10 travel faster than in air and preferably acoustic detection devices 20 are attached to the locomotion platform 10 so as to receive said vibrations; attachment means for acoustic detection devices 20 may include mechanical, adhesive, or moulding or any suitable attachment means to provide effective sound communication between locomotion platform 10 and acoustic detector 20. In one embodiment acoustic detection devices 20d may be placed on the floor 28 under said locomotion platform 10 and in another acoustic detection devices 20a, 20e may be placed inside 215 or outside 210 of said platform 10.

Of particular value to motion tracking 5 using acoustic detection devices 20 with locomotion platform 10 is a cavity 3 formed by locomotion platform 10 when in contact with floor 28. In such instance acoustic detection devices 20 are shielded from extraneous sound when attached on inside of cavity 3. Furthermore piezoelectric acoustic detection devices exhibit a useful signal to noise ratio for employing a time delay estimation algorithm to provide direction information.

Again with reference to Figures 2 and 4 there is provided a means of tracking motion 5 which is employs placement of acoustic detection devices 20 on or near the locomotion platform 10. A preferred shape for said platform 10 is substantially "dish" shaped and preferably the locomotion platform 10 is made from a single moulded piece.

Preferably a substantially dish shaped locomotion platform 10 is made from a polymer exemplified by: PTFE, PET, ABS, HDPE, UHMWPE, PA6, PA66 though other polymers or combinations, alloys and the like are also possible. More preferably a dish shaped locomotion platform 10 is made in a single piece by any polymer forming technology exemplified by thermoforming, vacuum moulding and injection moulding. Other forming approaches are possible. A locomotion platform 10 may also be formed in more than one section and joined together for use. With reference to Figure 2 and 4, there is preferably a single piece, convex dish shaped locomotion platform 10 used in association with acoustic detection devices 20, low friction footware 90, signal interpretation unit 35 and associated software that interacts with visual software and so synchronises motion on locomotion platform 10 with visual software imaged on screens 60, 80. Less preferred is a multi-piece locomotion platform 10 in which there is more than one joining facet.

Returning to Figure 2 there is provided a motion tracking means 5 wherein output from at least one acoustic detection device 20 provides motion control signal in accordance with those recognised by computer 40 driven by 2D or 3D visual software to achieve locomotion displayed by at least one imaging device 60, 80.

Preferably imaging device 80 is a head-mounted display. However a user of a locomotion platform 10 may advantageously stand in front of a computer visual display 60 and "walk" in the locomotion platform 10 and acoustic detection devices 20 translate movement of feet on the locomotion platform 10 by way of computer linked audio hardware 35 into motion on the visual display 60. Alternatively an imaging device 60 may be a front or back projection screen.

In preferred embodiments a motion tracking means 5 wherein a signal from acoustic detection devices 20 is amplified and interpreted by computer microphone audio card 35 and associated software. Such a combination is typically capable of stereo signal analysis (and hence processing signals from two acoustic sensors).

Acoustic detection devices 20 may be passive microphones exemplified by piezoelectric, electrostrictive and magnetostrictive technology or active microphones exemplified by condenser / capacitor technology. Advantageously, with reference to Figure 1 and Figure 2, at least two acoustic detection devices 20, 22 are mounted on or close to a surface of said locomotion platform 10. Close mechanical connection between acoustic detection devices 20, 22 and locomotion platform 10 achieves a good acoustic link and acoustic detection devices 20, 22 effectively pick up footware 90 motion of the user 15 walking on locomotion platform 10. With reference to Figures 1 and 7 the action of moving footware 90 over surface 200 of locomotion platform 10 generates noise and with reference to Figure 2, such noise when detected by acoustic detection devices 20, 22 may be advantageously used to control motion in computer driven visual software. Advantageously in one embodiment at least one acoustic detection device 20, 22 is used for noise cancellation to remove sound experienced by user 15 generated by motion of footwear 90 on a locomotion platform 10. Alternatively and advantageously a motion tracking means 5 is provided wherein at least two acoustic detection devices 20, 22 provide signal data input to computer driven 2D or 3D visual software providing locomotion and direction of motion translation between a locomotion platform 10 and visual software outputted to one or more visual display screens 80, 60.

The skilled person will appreciate that the use of acoustic detection device 20 in Figure 2, for noise cancellation, may be in conjunction with the or another acoustic detection device 22 to provide locomotion and direction of motion information to control computer driven software for translation between real and virtual worlds. Advantageously noise cancellation, locomotion and direction of motion may be simultaneously achieved by use of a suitable number of acoustic detection devices 20, 22.

Valuably, to assist determining motion and direction of motion of a user's 15 footware 90 when traversing the top surface 200 of a locomotion platform 10, the top surface 200 may be embossed with embossments 232, 234 shown schematically in Figure 5a and Figure 5b. Embossments may be positive 234 or negative 232 and may be of any shape. In one particular embodiment a pinseal emboss pattern is used. Advantageously the sliding of footware 90 over embossments 235 produces sound patterns that may be used to determine motion and direction of motion once detected by acoustic detection devices 20, 22 the outputs of which are interpreted by audio card hardware 35 and computer software (not shown).

With reference to Figure 2, there is provided a motion tracking means 5 for a locomotion platform 10 comprising a locomotion platform 10, at least one acoustic detection device 20, footware 90 worn by a user 15 using said locomotion platform 10 and at least one means 35 of interpreting signal from said at least one acoustic detection device 20, said interpretation influencing visual software driven by computer type hardware 40 and imaged by at least one imaging device 60, 80. Additionally and advantageously and with reference to Figure 5a and Figure 5b, there is provided in the surface 200 of locomotion platform 10, embossed patterns 235 and with reference to Figure 6 embossments 232 and 234 differ from each other in different regions of locomotion platform 10 thereby producing different sound patterns when footware 90 slides across different regions. Difference in sound patterns enable feet location and direction to be interpreted by means 35 of interpreting signal from at least one acoustic device 20, 22, interpretation influencing visual software driven by a computer type hardware 40 and imaged by at least one imaging device 80, 60.

Some example embodiments of the present invention will now be further described in more detail.

Example 1 : A locomotion platform (10) was made by way of vacuum thermoforming a 5.5mm thick sheet of HDPE of length 2000mm and width 1200mm. The HDPE sheet was pin-seal embossed on one major surface which becomes the top surface (200) of the thermoformed locomotion platform (10). To the underside (230) of the locomotion platform (10) a piezoelectric surface microphone (20) with 3.5mm jack socket is fixedly mounted using high tack adhesive tape and connected to the microphone socket on a Personal Computer (PC) (40) via a 3 metre long coaxial cable. The microphone socket of the PC is connected to a means of interpreting the signal, for example a "sound card" - which is both a signal amplifier and an analogue to digital converter - and accompanying software. The digital output is interpreted by software that removes transient noise and averages signal intensity to provide an envelope of the sound associated with each stride on the locomotion platform surface (200). The envelope height (amplitude) i.e. sound intensity, is converted to keyboard key-strokes. For example for the "W"- key which in game and other software may be used to move a character in a forward direction.

A user (15) wearing footware (90) having ceramic discs (460) with interface region (440) may initiate the motion tracking as follows: a) Initiate the sound card and sound interpretation software (35) b) Initiate the virtual reality scene software on PC (40)

c) Initiate the HMD (80)

d) The user steps on to the surface (200) of locomotion platform (10) with their legs in part stride, i.e. one leg forward and the other backward as shown schematically in Figure 1.

The user (15) then puts on HMD (80) (not shown in Figure 1 ) in which the user (15) will see a virtual world scene presented by HMD (80) and in which the user (15) is the first person. HMD (80) provides direction tracking. e) The user (15) then moves their legs by sliding footware (90) with interface regions (440) on ceramic discs (460) over locomotion platform (10) embossed surface (200) so as to exchange the feet positions which the user (15) continues to do in a reciprocating action.

Movement of footware (90) and interface region (440) over locomotion platform embossed surface (200) generates sound for each stride i.e. exchange of foot positions and this sound is picked up by the piezo-electric microphone (20), conveyed to sound card (35) is thereby amplified and digitised and via associated signal processing/smoothing software is converted to, say, the signal of a "W" key press. Thereby an ambulation step in the virtual reality scene software running on PC (40) presented to the user via HMD (80). The user (15) feels they are walking because their legs are moving and the virtual scene they are looking at, provided by HMD (80), moves accordingly. It will be appreciated that similar functionality may be achieved without the use of a HMD, though perhaps with a less immersive user experience. Example 2: In a second example the above-described approach of example 1 is employed with modifications. Thus in addition there a second surface mounted piezoelectric microphone (22) is fixedly mounted, for example using high tack adhesive tape, to the underside (230) of locomotion platform (10), preferably at 90 degrees to the first piezo-electric surface mounted microphone (20).

The output from each microphone (20) and (22) is fed, for example by independently coaxial cable(s), to sound card (35) in PC (40). The PC (40) sound card (35) has stereo input channels so that signals from microphones (20) and (22) are independently amplified and digitised. The difference in time of flight of sound through the locomotion platform (10) generated by each foot to each of the two substantially orthogonally placed microphones (20) and (22) provides sufficient information to find direction of motion of a user's (15) footware (90) relative to a starting position. The direction of feet movement is particularly valuable when direction of motion information is not otherwise available. Alternatively it may be employed to supplement directional information from, say, an accelerometer in in a head-mounted display.

In one example use case, a user (15) takes a snow-boarding stance on a locomotion platform (10) in front of a large screen (60) showing a virtual snow covered mountainside in which the user (15) is present as the first person. The user (15), facing the monitor screen (60), moves their feet. Footware (90) thereby generates sound that is picked up by microphones (20) and (22), and the sound from each microphone is separately amplified and digitised by sound card (35) and analysed by software, the combination providing a means of interpreting the signals so as to provide the virtual scene software with an "A" key or "D" key press for turning left or right respectively in the virtual scene. The amplitude of both signals provides speed of forward motion, effected by virtual "W" key presses. The user (15) is visually immersed in the virtual scene, which immersion is the more profound because their body and particularly leg movements provide changes to the visual scene as the user (15) expects.

Further aspects of the invention are set out in the following clauses:

1 . A motion tracking means (5) for a locomotion platform (10) comprising a locomotion platform (10), at least one acoustic detection device (20), footware

(90) worn by a user (15) using said locomotion platform (10) and at least one means (35) of interpreting signal from said at least one acoustic detection device (20), said interpretation influencing visual software driven by computer type hardware (40) and imaged by at least one imaging device (60, 80).

2. Footware (90) as recited in clause 1 that generates sound when sliding on said locomotion platform (10).

3. Footware (90) as recited in clause 2 wherein footware interface surface 440 differs between feet and generates different sound from each foot when sliding on said locomotion platform (10). 4. A locomotion platform (10) as recited in clause 1 wherein said at least one acoustic detection device (20) is close to, attached mechanically to, adhesively attached or moulded to a surface of said locomotion platform (10). 5. A means of tracking motion (5) as recited in clause 1 wherein said locomotion platform (10) is a single moulded piece and is substantially dish shaped (12).

6. A substantially dish shaped locomotion platform (10) as recited in clause 5 made from a polymer exemplified by: PTFE, PET, ABS, HDPE, UHMWPE, PA6, PA66.

7. A dish as recited in clause 6 wherein said dish comprises one or more formed sections wherein forming is exemplified by thermoforming or injection moulding 8. A motion tracking means (5) as recited in clause 1 wherein output from said at least one acoustic detection device (20) provides motion control signal in accordance with those recognised by computer (40) driven by 2D or 3D visual software to achieve locomotion displayed by said at least one imaging device (60, 80).

9. At least one imaging device (60, 80) as recited in clause 8 wherein said imaging device is emitting or projection screen technology (60) for one or more viewers, head mounted display (80) for an individual viewer or both. 10. A motion tracking means (5) as recited in clause 8 wherein signal from said acoustic detection device (20) is amplified and interpreted by computer microphone audio card (35) and associated software.

1 1. A motion tracking means (5) as recited in clause 1 wherein at least two acoustic detection devices (20, 22) are mounted on or close to a surface of said locomotion platform (10).

12. A motion tracking means (5) as recited in clause 10 wherein at least one of said at least two acoustic detection devices (20, 22) is used for noise cancellation to remove sound generated by motion of footwear (90) on said locomotion platform (10)

13. A motion tracking means (5) as recited in clause 10 wherein said at least two acoustic detection devices (20, 22) provide signal data input to said computer driven 2D or 3D visual software providing locomotion and direction of motion translation between said locomotion platform (10) and said visual software outputted to one or more screens (80, 60). 14. Top surface (200) of dish shaped locomotion platform (10) as recited in clause 6 wherein positive (234) or negative (232) embossments (200) are embossed in dish surface (200).

15. A dish shaped locomotion platform (10) as recited in clause 13 and footware (90) as recited in clauses 2 or 3 wherein said footware (90) produces sound patterns when sliding on said embossed patterns (200)

16. A motion tracking means (5) as recited in clause 14 comprising a dish shaped locomotion platform (10), footware (90) and embossment patterns (232, 234) and at least one acoustic detection device (20) wherein said embossment patterns are different in different regions of said dish (10) producing different sound patterns when said footware (90) slides across said different regions, said different sound patterns enabling feet location and direction to be interpreted by way of said means (35) of interpreting signal from said at least one acoustic device (20, 22) said interpretation influencing visual software driven by a computer type hardware (40) and imaged by at least one imaging device (80, 60). While various embodiments of the invention have been described the description is intended to be exemplary rather than limiting and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the invention. Accordingly the invention is not to be restricted except in the light of the attached claims supported by the description herein. No doubt many other effective alternatives will occur to the skilled person. For example aspects and embodiments of the present invention may be advantageously used in combination with the teachings of US7470218 (hereby incorporated by reference).

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, and the like described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Thus it will be understood that the invention is not limited to the described

embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.