Abstract:
A method of interfacing a person with a computer, the method comprising: providing the person with a device having: a shaft having an axis; a tsuba connected to the shaft and having a first side that extends away from the axis and faces the shaft; and a handgrip on a second side of the tsuba opposite the first side; acquiring an image of the device; determining an orientation of the device responsive to the image; and generating an action by the computer responsive to the orientation.

Description:
RELATED APPLICATIONS 
     The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application 61/056,027 filed May 26, 2008 the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to interfacing a human with a computer and optionally to integrating a person with a computer to generate a virtual reality. 
     BACKGROUND 
     In the beginning, there was the mouse and the keyboard. And the mouse and the keyboard interfaced the human and the computer. However, as technology developed, computers acquired capacity to receive and process data sufficient to provide a cornucopia of relatively complex, real time, user applications that use or require more seamless and natural interfacing with human users than that provided by the mouse and keyboard. 
     Among familiar applications that use or require enhanced human machine interfacing are, by way of example, voice recognition services that enable a user to input data to a computer by talking to it, cell phone computer games and virtual realities that operate in real time. Many of these applications require or can benefit from, a capability to interpret and/or use human gestures responsive to images of a person making the gestures. As a result, considerable research efforts and resources are invested in developing gesture recognition apparatus and algorithms capable of receiving visual data in real time and processing the data to recognize and interpret human gestures. 
     A human gesture is considered to be any conscious or unconscious element of body language that conveys information to another person and/or a computer. By way of examples, a gesture may be any conscious or unconscious facial expression made in response to another person and/or a computer, a hand or body pose or motion made in response to a challenge or stimulus provided by a video game, virtual reality environment or multimedia presentation. Gesture recognition technology (GRT), is considered to comprise hardware and/or software technology configured to recognize, interpret and/or use human gestures responsive to images of a person making the gestures. 
     SUMMARY 
     An aspect of some embodiments of the invention, relates to providing methods of determining a spatial location and/or orientation of an object used by a person to interact with a computer. 
     An aspect of some embodiments of the invention relates to forming the object having a structure comprising first and second parts that are useable to determine 3D spatial location and/or orientation of the object from an, optionally conventional, 2D image of the object. In an embodiment of the invention, a projection of the first part of the structure onto the second part of the structure in an image of the object provides an indication of the orientation of the object. Optionally, the first and second parts are used to determine position and/or orientation of the object responsive to a 3D “depth map” of the object and/or of a scene in which the object is located. 
     According to an aspect of some embodiments of the invention, the object is provided with an inventive configuration of fiducial markings for indicating location and/or orientation of the object. Optionally, the fiducial markings are used to determine orientation of the object from a conventional 2D image of the object. Optionally, the fiducial markings are used to determine location and/or orientation of the object responsive to a 3D depth map of the object and/or of a scene in which the object is located. 
     An aspect of some embodiments of the invention relates to determining the person&#39;s spatial location and body pose, also referred to as “posture”, and integrating the location and/or pose with the location and orientation of the object. 
     According to an aspect of some embodiments of the invention, the object is a simulation of a lightsaber, optionally for use by a player, hereinafter a “combatant”, in a star-wars type combat game generated and controlled by a suitable computer. 
     In an embodiment of the invention, a combatant holding the lightsaber is imaged to provide a video of the combatant, optionally using a 3D imaging system that provides real time video rate depth maps and images of the combatant. The depth maps and/or images are processed by the computer to determine 3D spatial location and orientation of the lightsaber and optionally location of the combatant and the combatant&#39;s posture as a function of time. The computer uses the location and orientation of the lightsaber and optionally of the combatant to animate an avatar holding a lightsaber in the star-wars combat game presented on a suitable video screen controlled by the computer. 
     For convenience of presentation, to distinguish the lightsaber held by the combatant from a lightsaber held by an avatar on a video screen, the avatar&#39;s lightsaber is generally referred to as an “avatar lightsaber” and the combatants lightsaber is generally referred to as a “combatant lightsaber”. 
     Optionally, the combatant lightsaber comprises a handgrip, a protective hand guard referred to as a “tsuba”, and a lightsaber “stub-shaft”. The handgrip and lightsaber stub-shaft are optionally substantially cylindrical and share a common axis, hereinafter referred to as a “lightsaber axis”. The tsuba is located along the lightsaber axis between the lightsaber stub-shaft and handgrip and extends away from the lightsaber axis so that from various viewpoints from which the lightsaber may be viewed, the stub-shaft is projected onto, i.e. “shadows”, at least a portion of the tsuba. Optionally, the tsuba is formed having a planar region substantially perpendicular to the lightsaber axis. Optionally, the planar region is characterized by a rotational symmetry relative to the lightsaber axis. Optionally the planar region is circular. A projection of the stub-shaft onto the tsuba in an image of the lightsaber acquired from a viewpoint of the 3D imaging system imaging the lightsaber provides an indication of the orientation of the lightsaber. Generally, orientation of the lightsaber affects a shape of the tsuba in an image of the lightsaber and optionally the imaged shape is used to determine orientation of the lightsaber. 
     Optionally, surface regions of the stub-shaft and tsuba are fabricated so that a projection of the stub-shaft on the tsuba is relatively easily determined. Optionally, surface regions of the tsuba and stub-shaft are configured to have reflectivities that differ sufficiently to aid in distinguishing the projection in an image of the combatant lightsaber. In an embodiment of the invention, surface regions of the tsuba are covered or formed to have a relatively high reflectivity for light that is used to image the lightsaber. 
     In an embodiment of the invention, the lightsaber is provided having at least one reflective fiducial that is relatively easily identified in an image of the lightsaber. The identified at least one fiducial is used to determine spatial location and/or orientation of the light saber responsive to location and orientation of the at least one bright fiducial in the image. 
     Optionally, the at least one reflective fiducial, hereinafter also referred to as a “bright fiducial”, comprises a reflective element shaped so that it appears to have a substantially same, relatively intense brightness when illuminated by light from a light source located near the camera. Optionally, the bright fiducial comprises a spherical region located at the tip of the lightsaber stub-shaft and having a center located substantially along the lightsaber axis. Optionally, the at least one reflective fiducial comprises an annular region having an axis of rotation substantially coincident with the lightsaber axis. In an embodiment of the invention, the at least one bright fiducial is identified responsive to its reflectivity. Optionally, the reflectivity is determined responsive to data provided by depth maps and images of the combatant and lightsaber provided by the 3D imaging system. 
     In an embodiment of the invention, for convenience of use and safety, the combatant lightsaber stub-shaft is relatively short and optionally is less than or equal to about 30 cm. Optionally, the combatant lightsaber comprises an activation mechanism operable by the combatant to provide a signal to the computer to indicate that the combatant lightsaber is activated. When not activated, the avatar lightsaber is shown having a stub-shaft that “mimics” the stub-shaft of the combatant lightsaber. When activated, the avatar lightsaber is shown having a relatively long “light blade” that extends from the avatar lightsaber tsuba and replaces the stub-shaft. Optionally, the activation mechanism comprises a mechanical mechanism operable to provide a visual cue that is detected by the 3D imaging system to provide a signal that activates the combatant and avatar lightsaber. Optionally, the activation mechanism comprises a circuit that is operated to activate the combatant and avatar lightsaber by pressing a button switch on the combatant lightsaber handgrip or by applying pressure to the handgrip. Optionally, the activation circuit comprises a light that gets turned on to indicate that the lightsaber is activated when the activation circuit is operated. Optionally, the computer determines that the circuit is operated and the light turned on responsive to an image provided by the imaging system that images the combatant and combatant light saber. Optionally, the activation circuit comprises a transmitter that transmits an “activation signal”, such as an RF signal, receivable by a suitable receiver coupled to the computer when the combatant lightsaber is activated. 
     In some embodiments of the invention, the lightsaber stub-shaft of the combatant lightsaber is configured to be fitted with a relatively long extension that simulates a light blade. Optionally, the extension is formed as a tube from a suitable light, but stiff, material, such as a polyurethane. The tube is formed having a lumen so that it may be securely mounted to the combatant&#39;s lightsaber stub-shaft. Optionally, the material from which the extension is made is substantially translucent and/or filled with a suitable translucent material and the lightsaber comprises a light source. When the lightsaber is activated, the extension is visibly illuminated along its length providing an impression of a light blade. 
     There is therefore provided in accordance with an embodiment of the invention, a method of interfacing a person with a computer, the method comprising: providing the person with a device having: a shaft having an axis; a tsuba connected to the shaft and having a first side that extends away from the axis and faces the shaft; and a handgrip on a second side of the tsuba opposite the first side; acquiring an image of the device; determining an orientation of the device responsive to the image; and generating an action by the computer responsive to the orientation. 
     Optionally, determining an orientation comprises determining a projection of the shaft on the tsuba. 
     Additionally or alternatively, determining an orientation optionally comprises determining a shape for the tsuba in the image relative to a known shape of the tsuba. Optionally, the tsuba has a circular periphery. Optionally, determining the shape of the tsuba in the image comprises determining a major and minor axis of the shape in the image. 
     In some embodiment of the invention the method comprises determining 3D spatial coordinates for the device responsive to the determined shape. 
     In some embodiment of the invention the method determining an orientation comprises determining a polar angle of the axis relative to a coordinate system. Optionally, determining a polar angle comprises removing a degeneracy in the determination of the polar angle. In some embodiment of the invention the method determining an orientation comprises determining an azimuth angle of the axis. 
     In some embodiment of the invention determining an orientation comprises: determining 3D spatial coordinates for each of three regions of the device in the image; determining whether the coordinates lie substantially along a same straight line; and using the coordinates to determine the orientation. 
     In some embodiment of the invention the method comprises providing the surface of the shaft and the first surface of the tsuba with relatively enhanced contrast. Optionally, providing relatively enhanced contrast comprises providing the surface of the tsuba with relatively high reflectivity. Additionally or alternatively, providing relatively enhanced contrast optionally comprises providing the surface of the shaft with relatively low reflectivity. 
     In some embodiment of the invention the method comprises providing the device with at least one fiducial marking to aid in locating a feature of the device. Optionally, the at least one fiducial marking comprises a relatively bright reflective fiducial at an end of the shaft. Optionally, the method comprises configuring the fiducial at the end of the shaft to have a substantially same brightness irrespective of orientation of the device. Additionally or alternatively, the fiducial at the end of the shaft optionally comprises a highly reflective spherical surface. In some embodiments of the invention, the at least one fiducial marking comprises a highly reflective region along the periphery of the tsuba. 
     In some embodiments of the invention, acquiring an image comprises acquiring a 3D depth map image of the device. 
     In some embodiments of the invention, acquiring an image comprises acquiring a contrast image of the device. 
     In some embodiments of the invention, generating an action by the computer comprises animating an avatar. Optionally, the avatar is located in a virtual reality. Optionally, animating the avatar comprises animating the avatar to interact with an element of the virtual reality. 
     In some embodiments of the invention, the method comprises, comprising determining 3D spatial coordinates for person. Optionally, determining spatial coordinates comprises acquiring a 3D depth image of the person and using the depth image to determine the coordinates. Additionally or alternatively, the method comprises determining location of the avatar in the virtual reality responsive to the determined coordinates. 
     In some embodiments of the invention, the method comprises, determining posture of the person. Optionally, determining posture comprises acquiring a 3D depth image of the person and using the depth image to determine posture. Additionally or alternatively the method comprises, determining posture of the avatar responsive to the determined posture of the person. 
     In some embodiments of the invention, the avatar is a first avatar in the virtual reality and the element is a second avatar operating in the virtual reality. Optionally, the second avatar is animated responsive to actions of a person. Optionally, the second avatar is animated in accordance with an embodiment of the invention. 
     In some embodiments of the invention, the virtual reality is a reality of a computer game. Optionally, the first and second avatars are engaged in combat with each other in the computer game. Optionally, the combat is a simulated star wars combat. 
     There is further provided in accordance with an embodiment of the invention, a computer readable medium comprising an instruction set for configuring a computer to interface with a person according to a method of any of the preceding claims. 
     There is further provided in accordance with an embodiment of the invention, a system for interfacing with a person comprising: a human operated device having: a shaft having an axis; a tsuba connected to the shaft and having a first side that extends away from the axis and faces the shaft; and a handgrip on a second side of the tsuba opposite the first side; imaging apparatus for acquiring imaging data of the device; and a computer configured to receive the imaging data and process the received data to determine an orientation of the device and generate an action responsive thereto. 
     Optionally, the system comprises a computer readable medium comprising an instruction set for configuring the computer to process the received data. Additionally or alternatively, the system comprises a computer readable medium comprising an instruction set for configuring the computer to generate the action. 
     Optionally, generating an action by the computer comprises animating an avatar. Optionally, the avatar is located in a virtual reality. Optionally, animating the avatar comprises animating the avatar to interact with an element of the virtual reality. Optionally, ein the avatar is a first avatar in the virtual reality and the element is a second avatar operating in the virtual reality. Optionally, the second avatar is animated responsive to actions of a person. 
     There is further provided in accordance with an embodiment of the invention, a method of interfacing a person with a computer, the method comprising: providing the person with a device having: a platform on which the person stands; a set of gimbals on which the platform is mounted that enables the person to change the orientation of the platform by shifting his or her weight on the platform; and at least one fiducial marking; acquiring an image of the at least one fiducial marking; determining an orientation of the device responsive to the image; and generating an action by the computer responsive to the orientation. Optionally, the at least one fiducial comprises a fiducial along an edge of the platform. Optionally, the at least one fiducial comprises two fiducial markings. Optionally, the two fiducial markings comprise at least two relatively close fiducial markings separated by a relatively small region along the edge that is not marked with a fiducial. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
       Non-limiting examples of embodiments of the invention are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. 
         FIG. 1A  schematically shows a perspective view of a combatant holding a lightsaber in accordance with an embodiment of the invention; 
         FIG. 1B  schematically shows a perspective enlarged view of the lightsaber held by the combatant in  FIG. 1A , in accordance with an embodiment of the invention; 
         FIG. 1C  schematically shows the lightsaber held by the combatant in  FIG. 1A  from a perspective different from that shown in  FIG. 1B , in accordance with an embodiment of the invention; 
         FIGS. 2A-2F  schematically show the lightsaber shown in  FIG. 1B  rotated through various angles about a same y-axis and how a projection of the lightsaber&#39;s stub-shaft on the lightsaber&#39;s tsuba and/or images of the lightsaber bright fiducials can be used to determine orientation of the lightsaber, in accordance with an embodiment of the invention; 
         FIGS. 3A-3E  schematically show the lightsaber shown in  FIG. 1B  rotated through various angles about a same x-axis and how a projection of the lightsaber&#39;s stub-shaft on the lightsaber&#39;s tsuba can be used to determine orientation of the lightsaber, in accordance with an embodiment of the invention; 
         FIGS. 4A-4F  schematically show the lightsaber shown in  FIG. 1B  rotated through various angles about an x-axis and a y-axis and how a projection of the lightsaber&#39;s stub-shaft on the lightsaber&#39;s tsuba can be used to determine orientation of the lightsaber, in accordance with an embodiment of the invention; 
         FIG. 5  shows a flow diagram of a method of determining location and orientation of a combatant lightsaber, in accordance with an embodiment of the invention; 
         FIG. 6  schematically shows a virtual reality star-wars combat being waged by two combatants, in accordance with an embodiment of the invention; 
         FIG. 7  schematically shows a lightsaber mounted with a light blade, in accordance with an embodiment of the invention; and 
         FIGS. 8A-8C  schematically show a skate board and bright fiducials on the skate board that are useable to determine orientation of the skate board, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  schematically shows a player, i.e. a combatant  21  holding a lightsaber  30 , shown greatly enlarged in  FIG. 1B , and engaged in a star-wars type lightsaber battle, in accordance with an embodiment of the invention. Combatant  21  is optionally interacting with a gaming system  50  comprising a 3D imaging system  52  having an optic axis  53  that provides a depth map as well as an image of the combatant at a video rate of at least thirty images and depth maps per second. 
     Any of various suitable video imaging cameras and 3D cameras known in the art may be comprised in 3D imaging system  52  to provide video rate images and depth maps of combatant  21 . Optionally, 3D imaging system  52 , is a gated 3D imaging system comprising an imaging camera for providing an, optionally conventional, image of a scene and a gated, time of flight 3D camera, for providing a depth map of the scene. Various types and configurations of gated time of flight 3D cameras and methods of gating them are described in U.S. Pat. Nos. 6,057,909, 6,091,905, 6,100,517, 6,445,884, 7,224,384, US patent Publication 2007/0091175, PCT Application IL2007/001571 and European Patent EP1214609, the disclosures of which are incorporated herein by reference. To image a scene and determine distances to objects in the scene using a gated 3D camera described in the referenced patents and application, the scene is illuminated with a train of, optionally IR, light pulses radiated from a suitable light source synchronized with gating of the camera. For each radiated light pulse in the train, following an accurately determined delay from the time that the light pulse is radiated, the camera is gated open for a period hereinafter referred to as a “gate”. Light from the light pulse that is reflected from an object in the scene is imaged on the photosurface of the camera if it reaches the camera during the gate. An amount of light registered by a pixel in the camera photosurface during the gate is used to determine distance to an object imaged on the pixel. 
     A suitable computer  54  receives images and depth maps from 3D imaging system  52  and processes the data provided by the images and depth maps to animate an avatar (not shown in  FIG. 1A ) that represents combatant  21  in lightsaber battle. The computer controls a suitable video screen  55  to display the combatant&#39;s avatar and an avatar, an “opponent avatar” (not shown in  FIG. 1A ), representing the combatant&#39;s opponent in the lightsaber battle. Optionally, computer  54  generates the opponent avatar without resort to a real combatant opponent. 
     In some embodiments of the invention the opponent avatar is generated responsive to another “real” player, i.e. a combatant opponent, who interacts with a gaming system similar to gaming system  50  and who is imaged by a 3D imaging system similar to that which images combatant  21 . Computers  54  of the two gaming systems communicate with each other so that the avatar animated responsive to combatant  21  and the opponent avatar are located and interact in a common virtual, star-wars reality that is presented to the combatant and opponent combatant on their respective video screens  55 . Interaction of a combatant and opponent combatant is illustrated in  FIG. 6  and discussed below. 
     Referring to the enlarged figure of lightsaber  30  schematically shown in  FIG. 1B , the lightsaber comprises a handgrip  31 , a protective hand guard, tsuba  32 , and a lightsaber “stub-shaft”  33  marked along its length with arcs for convenience of presentation. Handgrip  31  and lightsaber stub-shaft  33  are optionally substantially cylindrical and share a common axis  36 , hereinafter referred to as a “lightsaber” axis. The tsuba is located along lightsaber axis  36  between lightsaber stub-shaft  33  and handgrip  31  and extends away from the lightsaber axis. Optionally, tsuba  32  is formed having a planar region  37  substantially perpendicular to the lightsaber axis. Optionally, the planar region is characterized by a rotational symmetry relative to the lightsaber axis. Optionally, the planar region is circular. By way of example, in combatant lightsaber  33 , tsuba  32  is disc shaped. 
     Optionally, handgrip  31  comprises an activation button  39  controllable to operate an activation circuit having a transmitter (not shown) comprised in the handgrip. Activation button  39  is pressed to operate the transmitter to transmit a suitable signal, such as an optical or RF signal, to computer  54  to indicate to the computer that the lightsaber is activated. Upon activation, the computer turns on a relatively long light blade in an avatar lightsaber corresponding to lightsaber  30  that is shown on video screen  55  by the computer. 
     In some embodiments of the invention, tsuba  32  is provided with a configuration of fiducial markings advantageous for determining an orientation of lightsaber  30  that are highly reflective of, optionally IR, light used to image combatant light saber  30  and provide a depth map of the light saber. Optionally, substantially all the surface area of tsuba  32  on a side of the tsuba facing stub-shaft  33  is highly reflective for light used to image the saber. Optionally, at least a portion of a surface area on the rim of tsuba  32  or on a side of the tsuba facing handgrip  31  is highly reflective. 
     In an embodiment of the invention, surface of stub-shaft  33  has reflectivity that is less than that of reflectivity characterizing highly reflective surface regions of tsuba  32  but the stub-shaft does comprise a highly reflective bright fiducial located at an end of the stub-shaft far from tsuba  32 . The stub-shaft bright fiducial can be advantageous for determining a location and/or orientation of lightsaber  30 . Optionally, the bright fiducial comprises a highly, optionally IR, reflective spherical surface  34  of a body attached to the end of the stub-shaft. 
     Optionally, surface of handgrip  31  has reflectivity that is less than that of reflectivity characterizing highly reflective surface regions of tsuba  32  but does comprise a highly reflective bright fiducial located at an end of the handgrip far from tsuba  32  that can be advantageous for determining a location and/or orientation of lightsaber  30 . Optionally, the handgrip bright fiducial comprises a highly, optionally IR, reflective cylindrical surface  38 . Optionally the handgrip bright fiducial comprises an annular surface  40  schematically shown in  FIG. 1C . 
     In accordance with an embodiment of the invention, a projection of stub-shaft  33  onto tsuba  32  in an image of combatant lightsaber  30  acquired from a viewpoint of 3D imaging system  52  is used to provide location and/or orientation of the combatant lightsaber. Generally, orientation of the combatant lightsaber  30  affects shape of the tsuba in the image of the lightsaber and optionally the imaged shape is used to determine orientation of the lightsaber. For a given orientation of the combatant lightsaber  30 , size of tsuba  32  in the image may be used to determine location of the lightsaber. Optionally, location of stub-shaft bright fiducial  34  is used to provide location and/or orientation of combatant lightsaber  30 . Optionally, location of handgrip bright fiducial  38  and/or  40  is used to provide location and/or orientation of the lightsaber. 
     By way of example,  FIGS. 2A-4F  show schematic perspective images of combatant lightsaber  30  held by combatant  21  in  FIG. 1A  assuming that the combatant light saber is located substantially along optic axis  53  of 3D imaging system  52  and that the optic axis makes an angle of about 55° to a normal, i.e. the vertical, to the ground. The angle that the optic axis makes with the vertical ground is schematically indicated in  FIG. 1A . The figures schematically show combatant lightsaber  30  rotated through various angles, and indicate graphically how a projection of the lightsaber&#39;s stub-shaft  33  on the lightsaber&#39;s tsuba and/or images of the lightsaber bright fiducials  34  and/or  38  can be used to determine orientation of the lightsaber, in accordance with an embodiment of the invention. The figures also indicate graphically how images of the tsuba and bright fiducials can be used to determine distance of combatant light saber  30  from 3D imaging system  52 . 
       FIGS. 2A-2F  schematically show combatant lightsaber  30  rotated through various angles about a same y-axis. 
       FIG. 2A  schematically shows a perspective view of combatant lightsaber  30  being held upright with lightsaber axis  36  substantially perpendicular to the ground. Lightsaber axis  36  in  FIG. 2A  is assumed to be along a z-axis of a coordinate system having x and y-axes indicated in  FIG. 2A  that are coplanar with the surface of tsuba  32  facing stub-shaft  33 .  FIGS. 2B-2F  schematically show perspective images of lightsaber  30  rotated about the y-axis shown in  FIG. 2A  by angles 20°, 40°, 50° 60° and 90° respectively. In  FIGS. 2B-2F , the lightsaber is not rotated about the x-axis. 
     Shown below each figure is an image of the combatant lightsaber&#39;s tsuba  32 , its stub-shaft bright fiducial  34  and handgrip bright fiducial  38 . The rotation angle at which the combatant lightsaber is rotated is shown below the tsuba. For each figure, a projection of the combatant lightsaber&#39;s stub-shaft  33  onto the lightsaber&#39;s tsuba  32  is removed from the tsuba for the rotation angle at which the lightsaber is imaged by 3D imaging system  52  and shown in the figure. The region removed from the tsuba is a portion of the tsuba that is hidden by the stub-shaft at the angle at which the combatant lightsaber is imaged in the figure and is removed for convenience of presentation to clearly show dependence of the projection on combatant lightsaber orientation. As noted above, in accordance with an embodiment of the invention, stub-shaft  33  has a surface that contrasts with the surface of tsuba  32  so that the portion of the tsuba that is hidden by the stub shaft is relatively easily recognized in an image of combatant lightsaber  30  acquired by 3D imaging system  52 . 
     From  FIGS. 2A-2F  it is seen that the various rotation angles for which lightsaber  30  is rotated in the figures are readily distinguished from the projection of stub-shaft  33  on tsuba  32  in accordance with an embodiment of the invention. It is further seen that images of stub-shaft bright fiducial  34  and handgrip bright fiducial  33  also provide information that is useable to determine locations and/or orientation of combatant lightsaber  30 , in accordance with an embodiment of the invention. 
     In accordance with an embodiment of the invention, the imaged shape of tsuba  32  is used to determine orientation of lightsaber  30 . From the images of tsuba  32  shown in  FIGS. 2A-2F  it is seen that whereas the tsuba is, optionally, circular, it assumes various different elliptical shapes in the images that are dependent on the 3D spatial orientation of lightsaber  30  and that orientation of the elliptical shapes in the images are also dependent on the lightsaber orientation. A distance of combatant lightsaber  30  from 3D imaging system  52  is optionally determined from a ratio between a size of a major axis of tsuba  32  in an image of the lightsaber and an actual diameter of the tsuba. 
       FIGS. 3A-3E  are similar to  FIGS. 2A-2F  and show perspective images of lightsaber  30  for rotations only about the x-axis shown in  FIG. 3A . Below the lightsaber in each figure the lightsaber&#39;s tsuba  32  is shown absent an area of the tsuba that corresponds to a projection of the lightsaber&#39;s stub-shaft  33  at the angle at which the lightsaber is imaged by 3D imaging system  52  and shown in the figure. Again it is seen, that in accordance with an embodiment of the invention, the various orientations of the lightsaber shown in  FIGS. 3A-3E  can readily be distinguished from images of tsuba  32 . 
       FIGS. 4A-4F  show perspective images of combatant lightsaber  30  rotated about both the x-axis and the y-axis. As in  FIGS. 2A-2F  in each  FIG. 4A-4F  the lightsaber&#39;s tsuba  32  with projection removed is shown below the lightsaber, and below the tsuba, the angles of rotation are shown. From the figures, it is seen that the orientations of combatant lightsaber  30  are readily distinguished by the projections of the lightsaber&#39;s stub-shaft on its tsuba. 
       FIG. 5  shows a flow diagram of an algorithm  300  used to determine location and orientation of combatant lightsaber  30 , in accordance with an embodiment of the invention. 
     In a first block  302 , 3D imaging system  52  acquires an, optionally IR, intensity image of combatant lightsaber  30  ( FIGS. 1A-1C ) and a depth map of the lightsaber. In a block  304  computer  54  optionally processes the image to locate regions of the image that are candidates for being tsuba  32 , stub-shaft bright fiducial  34  and handgrip bright fiducial  38  and/or  40 . Location of image regions that are candidates for the tsuba and bright fiducials is aided by the relatively high IR reflectivity that characterizes surfaces of the tsuba and bright fiducials. Upon locating three candidate image regions, optionally in a block  306 , each candidate region is identified with a different one of tsuba  32 , stub-shaft bright fiducial  34  and handgrip bright fiducial  38  or  39 . 
     Identifying a candidate region with tsuba  32 , stub-shaft bright fiducial  34  or handgrip bright fiducial  38  or  39  is aided not only by the optionally substantially different shapes of the tsuba, stub-shaft bright fiducial and handgrip bright fiducial. In accordance with an embodiment of the invention, distance between tsuba  32  and stub-shaft bright fiducial  34  is different than that between the tsuba and handgrip bright fiducial  38  and/or  40 . In an image of combatant lightsaber  30 , an image of tsuba  32  will always lie between an image of stub-shaft bright fiducial  34  and an image of handgrip bright fiducial  38  and/or  40 . And in general, the different actual distances between tsuba  32  and stub-shaft bright fiducial  34  and handgrip bright fiducial  38  or  39  correspond to different distances between their respective images in an image of the lightsaber. As a result, different distances between candidate image regions can be, and optionally are, used to aid in identifying candidate regions with features of lightsaber  30 . 
     In a block  308 , optionally, each candidate image region is used to determine a center point that lies on axis  36  of combatant lightsaber  30  for the feature of lightsaber  30  for which it is a candidate. For example, if an image region appears to be a candidate for tsuba  32 , the candidate region is used to determine a center point for the tsuba. 
     In a block  310  the center points are tested to determine if they satisfy a predetermined criterion for lying along a same straight line. If they are determined to lie along a same straight line, algorithm  300  optionally advances to a block  312 . In block  312  distances to points along the straight line provided by the depth map are used to determine a distance of combatant lightsaber  30  from 3D imaging system  52 . Optionally, the distance is a distance of the center point determined for tsuba  32  in block  308 . Optionally, the distance is an average of distances for points along the straight line determined for the center points. 
     In a block  314  a polar angle “θ” that combatant lightsaber axis  36  ( FIG. 1B ) makes with optic axis  53  of 3D imaging system  52  is determined responsive to the determined distance, a model of the optics of the 3D imaging system  52  and the image of the lightsaber. It is noted that the polar angle θ is determined to within a degeneracy of order 2, i.e. for a given image there are two solutions for the polar angle θ, one for which stub-shaft bright fiducial  34  (FIG.  1 B) is closer to 3D imaging system  52  and one for which the bright fiducial is farther from the imaging system. In accordance with an embodiment of the invention, configuration of tsuba  32  and bright fiducials  34  and  38  and/or  40  are used to determine which solution is adopted. In a block  316  an azimuthal angle φ for lightsaber axis  36  relative to optic axis  36  is determined responsive to the configuration of tsuba  32  and bright fiducials  34  and  38  in the image of the lightsaber. 
     If in decision block  306  three candidate image regions are not identified, or if in decision block  310  centers for candidate image regions are determined not to lie along a same straight line, algorithm  300  optionally advances to a decision block  318 . In decision block  318 , a decision is made as to whether a candidate region for tsuba  32  suitable for determining polar and azimuthal angles θ and φ exists in the image of combatant lightsaber  30 . If such a candidate is found, in a block  320  a configuration of the candidate image region identified with the tsuba, and if it exists, an image region identified with a bright fiducial, are used to determine polar and azimuthal angles θ and φ. 
     If in block  318  a decision is made that a suitable candidate for tsuba  318  is not found processing of the acquired image and depth map to determine location and orientation of combatant light saber  30  is abandoned and the algorithm returns to block  302  to acquire another image and depth map. 
       FIG. 6  schematically shows combatant  21  engaged in a lightsaber battle with another combatant  121  also equipped with a gaming system  50  and wielding a lightsaber  130 . For convenience of presentation an inset  181  shows an enlarged image  55 * of video screens  55  comprised in gaming systems  50 . Enlarged screen  55 * shows what combatants  21  and  121  see on their respective gaming system screens, in accordance with an embodiment of the invention. 3D imaging systems  52  of respective combatants  21  and  121  determine 3D spatial locations of the combatants, and optionally their body postures from 3D images provided by the 3D imaging system and 3D spatial positions and orientations of their lightsabers  30  and  130  as described above. 
     Each computer  54  transmits imaging, position and orientation data to the other computer to enable the computers to generate a common self consistent virtual reality star-wars venue inhabited by avatars  22  and  122  shown on video screens  55  that are animated responsive to motion of combatants  21  and  121  respectively. Avatars  22  and  122  wield avatar lightsabers  31  and  131  respectively that are shown on video screens  55 . When combatant  21  or  121  activates his or her activation button  39  ( FIG. 1B ) on lightsaber  30  or  130  respectively, corresponding combatant lightsaber  31  or  131  glows with an activated light blade  32  or  132 . A lightsaber  31  or  131  activated by its corresponding combatant  21  or  121  can be animated to deliver a blow and damage the opposing combatant&#39;s avatar  122  or  22  respectively by the corresponding combatant appropriately moving and wielding lightsaber  30  or  130 . A blow being delivered by avatar  22  or  122  can also be parried by opponent avatar  122  or  22  if the opponent avatar&#39;s combatant  121  or  21  is skillful enough to appropriately wield his or her lightsaber  130  or  30  respectively. A combatant  21  or  121  animates avatar  22  or  122  and the avatars lightsaber  31  or  131  responsive to locations and motion of the avatars in the virtual reality star-wars battle displayed on video screens  55 . Contact between avatars and objects in the virtual reality star-wars venue, such as contact between avatar lightsabers  31  and  131  and opponent avatars  122  and  22  is determined using any of various methods known in the art, such as by use of appropriate z-buffers. 
     It is noted that there are various methods and formats for displaying a virtual reality venue and avatars that inhabit the venues. In  FIG. 6  each combatant  21  and  121  sees only a portion of his or her own avatar and observes the avatar&#39;s light blade as if in front of combatants eyes. Other methods of presenting a virtual reality and avatars can of course be used and can be advantageous. For example, each computer  54  can control its corresponding video screen to show all of both avatars. 
     In some embodiments of the invention, a lightsaber such as a lightsaber similar to lightsaber  30  is equipped to receive a lightweight simulated light blade and the lightsaber comprises a suitable light source for lighting up the light blade when the lightsaber is activated.  FIG. 7  schematically shows a lightsaber  200  mounted with a lightweight light blade  202  that fits over a lightsaber stub-shaft  203 . Light blade  202  is formed from a material that diffuses and reflects light and lightsaber  200  comprises a light source  204 , which when turned on causes the length of light blade  202  to glow. For example, light blade  202  is optionally formed as a tube of polyurethane having internal walls that diffusively scatter light. Optionally, light blade  202  comprises a bright fiducial  206  in the form of a ring externally mounted to the light blade. 
       FIGS. 8A-8C  schematically show a skateboard  400  having bright fiducial markings  401  and  402  that are used to determined orientation of the skate board in accordance with an embodiment of the invention. Each figure shows a schematic photosurface  420  comprised in 3D imaging system  52  on which the skateboard is imaged. Schematic images  411  and  412  of bright fiducial markings  401  and  412  are shown on photosurface  420  for different orientations of skateboard  400 .  FIG. 8A  schematically shows how images of bright fiducials  401  and  402  on photosurface  420  change with change in yaw angle of skateboard  400 .  FIG. 8B  schematically shows how images of bright fiducials  401  and  402  on photosurface  420  change with change in pitch of skateboard  400 .  FIG. 8C  schematically shows how images of bright fiducials  401  and  402  on photosurface  420  change with change in roll angle of skateboard  400 . 
     It is noted of course that the skate board referred to above is not necessarily a real skate board, but may be any suitable skate board simulator. For example, the simulator optionally comprises a board having a shape similar to that of a skate board but instead of being mounted on wheels is optionally mounted on a set of gimbals that enables a person using the simulator to simulate motion on a skate board. 
     In the description and claims of the present application, each of the verbs, “comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily an exhaustive listing of members, components, elements or parts of the subject or subjects of the verb. 
     The invention has been described with reference to embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the described invention and embodiments of the invention comprising different combinations of features than those noted in the described embodiments will occur to persons of the art. The scope of the invention is limited only by the following claims.