fig1 a schematically shows a player , i . e . a combatant 21 holding a lightsaber 30 , shown greatly enlarged in fig1 b , 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 fig1 a ) 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 fig1 a ), 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 fig6 and discussed below . referring to the enlarged figure of lightsaber 30 schematically shown in fig1 b , 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 fig1 c . 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 , fig2 a - 4f show schematic perspective images of combatant lightsaber 30 held by combatant 21 in fig1 a 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 fig1 a . 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 . fig2 a - 2f schematically show combatant lightsaber 30 rotated through various angles about a same y - axis . fig2 a 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 fig2 a is assumed to be along a z - axis of a coordinate system having x and y - axes indicated in fig2 a that are coplanar with the surface of tsuba 32 facing stub - shaft 33 . fig2 b - 2f schematically show perspective images of lightsaber 30 rotated about the y - axis shown in fig2 a by angles 20 °, 40 °, 50 ° 60 ° and 90 ° respectively . in fig2 b - 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 fig2 a - 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 fig2 a - 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 . fig3 a - 3e are similar to fig2 a - 2f and show perspective images of lightsaber 30 for rotations only about the x - axis shown in fig3 a . 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 fig3 a - 3e can readily be distinguished from images of tsuba 32 . fig4 a - 4f show perspective images of combatant lightsaber 30 rotated about both the x - axis and the y - axis . as in fig2 a - 2f in each fig4 a - 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 . fig5 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 ( fig1 a - 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 ( fig1 b ) 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 ( fig1 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 . fig6 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 ( fig1 b ) 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 fig6 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 . fig7 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 . fig8 a - 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 . fig8 a schematically shows how images of bright fiducials 401 and 402 on photosurface 420 change with change in yaw angle of skateboard 400 . fig8 b schematically shows how images of bright fiducials 401 and 402 on photosurface 420 change with change in pitch of skateboard 400 . fig8 c 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 .
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 .