Patent Publication Number: US-7587747-B2

Title: Telepresence method and apparatus for simultaneous use by multiple active/passive users

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is a divisional of U.S. patent application Ser. No. 09/177,356 filed Oct. 23, 1998 now U.S. Pat. No. 7,190,392 and which claims priority from U.S. Provisional Application Ser. No. 60/063,232 filed Oct. 23, 1997. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to communication of images and, more particularly, to telepresence, including remote video monitoring. 
   2. Discussion of Related Art 
   Remote monitoring systems are known to include remotely located video cameras positioned for monitoring from a remote site with a personal computer or display. Such can be connected by any kind of connection such as point-to-point with a telephone line, via the internet or through an internet hub. A video server is used to capture successive real time images from a video camera, digitize and compress them and transfer them frame-by-frame through the internet, intranet or point-to-point protocol direct dial-in connection. 
   Telepresence is similar in concept to “virtual reality” except images and other stimuli are provided to the user via a connection in a telecommunications network. One approach uses a teleoperated camera platform coupled to the head movements of a remote user wearing a head-tracked, head-mounted display (HTHMD). See U.S. Pat. No. 5,436,638 at column 1, lines 43-48 and column 3, lines 10-31. Instead of a HTHMD, a desktop display can be yoked to the movements of a user seated before the display such as shown in FIGS. 13, 14A, 14B and 16 of U.S. Pat. No. 5,436,638. See also the PUSH desktop display and the BOOM3C head-coupled stereoscopic display, either hand-guided or hands-free (head-guided), of Fakespace, Inc., Menlo Park, Calif. Another approach is to use a remote reality engine with prerecorded scenarios for selection over the network according to monitored movements of the user. Due to the limited bandwidth typically available for such connections, the rate of frame delivery is very slow and therefore there is a noticeable lag between the time of image capture or retrieval and display. Moreover, the amount of video information conveyed is rather limited since the technology is based on the existing NTSC infrastructure. Consequently, the above described applications for telepresence tend to be lacking in the “presence” aspect and likewise remote viewing tends to be confined to rather static, e.g., industrial plant process monitoring, employee parking lot monitoring, security monitoring for plant ingress/egress and the like. 
   However, various competing transport technologies are now being deployed to increased the bandwidth enormously and thereby speed up such connections. These include optical fiber networks, cable, satellite and techniques to utilize the existing telephony infrastructure of twisted copper pairs as digital subscribers lines. Included in the services deliverable on the links provided according to such technologies will be HDTV. While the bandwidth of such links now being deployed to subscribers can be heavily proportioned in the downstream direction, they also provide at least a significant amount of upstream bandwidth. As a result, there will now be new opportunities for far more dynamic types of telepresence applications, including remote video monitoring, particularly on the Internet, and in ways heretofore never even contemplated. In particular, it can be foreseen that there will be extremely high demand for exciting, new telepresence application. 
   Unfortunately, these telepresence applications suffer from an underlying assumption borrowed from the art of “virtual reality” where the user is enabled to navigate within a virtual environment in a highly autonomous manner. The user takes command of the virtual environment and actively controls all of the responses of the reality engine according to monitored activity of the user. This dedication to a single user of the tools needed to generate the virtual environment makes the reality engine unavailable to all but this one user at a given time. A similar situation exists for a remotely located video camera. Since these tools are quite expensive, the cost of use for the single user is high. Hence the anticipated demand cannot be efficiently and economically met. 
   SUMMARY OF THE INVENTION 
   As object of the present invention is to provide a new type of telepresence, including remote monitoring, that takes advantage of the increased bandwidth on links now being deployed. 
   Another object of the present invention is to provide telepresence to more than one user at a given time. 
   According to a first aspect of the present invention, a system for providing video images, comprises a video camera for providing video signals indicative of said video images captured by said video camera, a first display, responsive to said video signals, for providing said video images for viewing by a first user, an n-axis sensor, responsive to n-axis first display motions caused by said first user, for providing an n-axis attitude control signal, an n-axis platform having said video camera mounted thereon, responsive to said n-axis attitude command signal, for executing n-axis platform motions emulative of said n-axis first display motions, and one or more second displays, responsive to said video signals, for providing said video images for viewing by one or more corresponding second users and responsive to said n-axis attitude command signal for executing n-axis second display motions emulative of said n-axis first display motions. 
   According to a second aspect of the present invention, a system comprises at least one reality engine for providing an image signal indicative of images taken from various attitudes, and a telepresence server, responsive to said image signal, for providing said image signal and an attitude control signal to at least one attitudinally actuatable display via a telecommunications network for attitudinally actuating said display for guiding a viewing attitude of a user and for displaying said images for said user of said at least one attitudinally actuatable display for passively viewing said images from said various attitudes. The telepresence server can be for providing access to said reality engine for an active user of a display attitudinally actuatable by said active user for providing said attitude control signal to said reality engine and to said telepresence server wherein the user is drawn from the general public with no special training. Or, the telepresence server can be for providing access to said reality engine for a trained director who can be local, not needing network access to the server, or remote, needing to access via a network. 
   According to a third aspect of the present invention, a display device comprises an n-axis display platform, responsive in a passive mode to an attitudinal control signal, for guiding a user&#39;s head to execute attitudinal movements, and responsive in an active mode to attitudinal movements of a user&#39;s head for providing sensed signals indicative of said attitudinal movements, and a display connected to said n-axis display platform, responsive to a video signal, for displaying images corresponding to said attitudinal movements. 
   These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  shows a prior art remote monitoring application; 
       FIG. 2  shows plural cameras mounted on corresponding n-axis platforms for being moved in an n-axis manner to monitor remote sites under the control of corresponding plural remote viewers each using a display such as a head mounted display having its attitude and/or position monitored in a corresponding n-axis manner; 
       FIG. 3  illustrates that one or more of the remote viewers may be passive viewers whose attitudinal head movements are not monitored at all but rather are guided to emulate the attitudinal head movements of an active viewer; 
       FIG. 4  shows one type of display for use by a passive viewer, according to the present invention; 
       FIG. 5  shows a telepresence server with a reality engine under the control of an active user, a local director, or a remote director and a plurality of passive users all interconnected by a communications network; 
       FIG. 6  shows a three-axis display that is usable in an active mode or a passive mode; 
       FIG. 7  shows a monitor screen where a user can choose a reality engine located at a remote tourist site for remotely viewing the chosen site; and 
       FIG. 8  shows the three-axis display such as shown in  FIG. 6  in schematic block diagram form connected to the communications network of  FIG. 5  via a signal processor. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1  shows a prior art internet remote video monitoring application where a user  10  of a personal computer (PC)  12  can access the internet  14  via a modem  16  and a local internet service provider (ISP)  18 . Another service provider  20  is connected via a router  22  and a hub  24  to a plurality of video servers  26 , . . . ,  28  which are in turn connected to a plurality of video cameras  30 , . . . ,  32 . The cameras can be located in different parts of an industrial plant such as the factory  34  and the warehouse  36 . In this way the user  10  can monitor various parts of the plant remotely. It is even possible to remotely control the camera, e.g., by controlling their lenses  38 ,  40  to zoom in and out. It should be realized, however, that the camera or cameras can be located anywhere and that the internet  14  can be any kind of connection or connections provided that bidirectionality is provided. 
   Given the typical bandwidth limitations of existing methods, such as methods for accessing the internet and other similar connections, this way of remote video monitoring has been found to be effective for rather static type applications such as security monitoring. E.g., a security officer sits before a PC or other display (or bank or displays) and monitors the desired points in various plants of a company from a single remote monitoring site. For this sort of application, a need for a large amount of bandwidth is not particularly important and hence the proven success of such relatively static applications. On the other hand, more dynamic remote video monitoring applications, such as entertainment or education, cannot be expected to be viable using such limited bandwidth connections. 
   Telepresence concepts are shown implemented in  FIG. 2  in a wideband network. A wideband internet service provider (WISP)  42  is shown connected to a plurality of displays for users at different geographical locations. The WISP  42  may be owned by a local telephone or cable TV company, for example, and can provide broadband services on any of the competing media illustrated such as a copper pair  44 , coaxial cable  46 , an optical fiber  48 , or equivalents such as wireless including satellite communications. Each of these will deploy their own peculiar subscriber interfaces  50 ,  52 ,  54  respectively. For instance, the twisted copper pair may be used as an Asymmetric Digital Subscriber Line (ADSL) using, e.g., Discrete MultiTone (DMT), Carrierless Amplitude Phase (CAP) modulation, or the like, and terminate with an interface  50  comprising an ADSL modem. Of course, other types of so-called xDSL technologies can be used as well. These include but are not limited to IDSL (ISDN DSL), HDSL (High-bit-rate DSL), SDSL (Symmetric DSL), RADSL (Rate-Adaptive DSL), and VDSL (Very-high-rate DSL). On the other hand, the cable interface  52  might simply be a part of a set top converter, for example, also used for conventional television as modified for web access, e.g., by the WebTVNetworks unit of Microsoft, or by other providers such as Oracle Corp., Sun Microsystems Inc., Netscape Communications, General Instrument, Thomson SA, WorldGate Communications Inc., or the like. The fiber interface  54  might be an optical network unit (ONU) that converts downstream optical signals to electrical and formats them for a copper or cable connection to the subscriber and the reverse for upstream signals. The fiber  48  could also terminate in the user&#39;s premises. It should be mentioned that other delivery systems are possible as well, including LMDS. Similarly, the internet is presently being augmented to service increased bandwidth requirements. 
   Considering the enormously increased bandwidth provided by the WISP  42  e.g., 7 or 8 Mbit/sec compared to 33 kbit/sec for the modem  16  of  FIG. 1 , it is now possible to provide new and more dynamic functions for remote video monitoring. For instance,  FIG. 2  shows Head Mounted Displays (HMDs)  56 ,  58 ,  60  for use by three different subscribers connected to the respective interfaces  50 ,  52 ,  54  by signal lines  62   a ,  64 ,  66  which can be bidirectional. Bidirectionality may be employed for conveying broadband video information downstream and command data upstream in a narrowband. The command data may be entered through a PC (not shown) or by means of input devices on the HMD itself, for example. It should be realized that the example of  FIG. 2  does not exclude the coexistence of the possible transmission of wideband information, such as video, from the subscriber to the network as well, such as by using SDSL, mentioned above, or by making ADSL behave symmetrically although with a reduced downstream rate. 
   Various head mounted displays are known. One type is a see-through display where the real world view of the user is “augmented” with imagery from an image source, called “augmented reality”. Another type completely blocks light from the outside and is for use in a completely virtual environment. Yet another type is a “video see-through” where the user wears stereo cameras on his head which provide images for perception of the surroundings using a head mounted display. All of these types of HMDs can be used to implement the present invention. However, many of these displays use bulky optics and related heavy cables which are somewhat burdensome. Moreover, presently available optics have a rather narrow field of view and present video image resolution is rather poor. 
   A particularly attractive recent innovation for the purposes of the present invention is the retinal display which does away with the external display and the associated optics entirely. There is no comparable problem with narrow field of view and low resolution with a retinal display. A retinal display has been disclosed for providing a scanning light signal for the formation of images firstly and directly in the eye of a viewer: U.S. Pat. No. 5,467,104 shows the projection of a modulated scanning light signal directly onto the retina of the viewer&#39;s eye without the prior formation of any real or aerial image outside the viewer&#39;s eye. In other words, light rays do not converge in any way outside the eye to form an image. That patent shows modulated photons of the light signal reflected from one or more scanners by way of projection optics directly onto the retina. A micromechanical scanner can be used as the scanning device, as shown in U.S. Pat. No. 5,557,444 (based on U.S. patent application Ser. No. 08/329,508, filed Oct. 26, 1994). An optical fiber may be used to provide the light signal from the photon source to the scanner as shown in U.S. Pat. No. 5,596,339 in order to promote a lightweight, head mounted, panoramic display. 
   In addition to the HMDs  56 ,  58 ,  60 , a respective plurality of attitude sensors  62 ,  64 ,  66  are shown for mounting on the head of the user for sensing the rotational movements of the user&#39;s head and providing a sensed signal on a line  68 ,  70 ,  72 , respectively, to interfaces  50 ,  52 ,  54  for upstream transmission. Such a device for determining orientation of a user&#39;s head using accelerometers is shown in U.S. Pat. No. 5,615,132 to Horton et al. Another is shown in U.S. Pat. No. 5,645,077 to Foxlin. Yet another is provided by Precision Navigation, Inc., 1235 Pear Avenue, Suite 111, Mountain View, Calif. 94043. For a simple case, it is assumed that translatory position (translation) of the user&#39;s head is not measured or, if measured, is ignored. A further simplification reduces the number of rotational degrees of freedom that are measured from three to two (e.g., pan (yaw) and tilt (pitch) as described below), or even just one. This simplification does exclude the measurement of translations, however. The WISP  42  is connected by a signal on a line  74  and via the internet  76  and a signal on a line  78  to another WISP  80  connected in turn to a plurality of video servers  82 ,  84   86  signals on lines  87 ,  88 ,  89 . It should be realized that there need not be two separate WISP&#39;s  42 ,  80 , but that in certain circumstances one can suffice. The video servers are connected to a corresponding plurality of cameras  90 ,  91 ,  92  by a plurality of signal lines  94 ,  96 ,  98 . The cameras  90 ,  91 ,  92  send video signals via the internet  76  to the HMDs  56 ,  58 ,  60 , respectively, for display. 
   In the opposite direction, the interfaces  50 ,  52 ,  54  transmit attitude command signals in response to the corresponding sensed attitude signals on the lines  68 ,  70 , 72  from the attitude sensors  62 ,  64 ,  66  through the WISP  42 , the internet  76 , the WISP  80  and the plurality of video servers  82 ,  84 ,  86  to a corresponding plurality of n-axis platforms such as three axis platforms  100 ,  102 ,  104 . 
   The platforms  100 ,  102 ,  104  need not be three-axis, i. e., including pitch, roll and yaw but may be restricted to only two axes (e. g., pitch and yaw) or even just one (e. g., yaw). For instance, if roll is omitted, a 2-axis platform in the form of a computer controlled pan-tilt (2-axis: yaw-pitch) unit, Model PTU-46-70 or PTU-46-17.5, produced by Directed Perception, Inc., 1485 Rollins Road, Burlingame, Calif. 94010 may be used. Actuators from other manufacturers such as Densitron may be used as well. In addition to one or more of the three attitudinal degrees of freedom, one or more of the three translational degrees of freedom may also be added in any desired combination. For example, a six degree of freedom platform could be provided. 
   While some of the attitudinal or positional degrees of freedom discussed above may be added or subtracted in a given application in different combinations, it should be realized that other degrees of freedom that are different in kind from those discussed above may also be added to an n-axis platform. For instance, the attitude sensor  62 , as shown in  FIG. 3 , can be sensing 2-axes only, e. g., yaw (pan) and pitch (tilt) while an additional eye attitude sensor  106 , as shown in  FIG. 3  can be added for monitoring two degrees of freedom of the HMD  56  user&#39;s eyes. The eye sensor  1056  provides a sensed signal on a line  108  to the interface  50 . In that case, a four-degree of freedom, i. e., 4-axis platform  100  would be appropriate. Two axes for emulating the pitch and yaw of the user&#39;s head and two axes for emulating the pitch and yaw of at least one of the user&#39;s eyes. A 4-axis platform (“The vision-head”) for carrying out the above is shown by the ESCHeR high performance stereo-head at the following internet site provided by Rougeaux Sebastian:http//www.etl.go.jp/etl/robotics/Projec . . . 6/node4.html#SECTION0002100000000000 0000. See also http://www.etl.go.jp/etl/robotics/Projects/CogRobo/escher.html. Other camera motion platforms are available, for instance from Helpmate Robotics Inc., Shelter Rock Lane, Danbury, Conn. 06810-8159 under the product names BiSight/UniSight and Zebra at http://ntplx.net/˜helpmate/. Another 4-axis Stereo-Vision Head (TO 40) can be obtained from Robosoft, Technopole d=Izarbel F-64210 Bidart, France at http://www.robosoft.fr. 
   Thus various combinations of monitoring of degrees-of-freedom of body parts can be used. Not only selected head and/or eye attitudinal degrees-of-freedom but also translatory (positional) degrees-of-freedom of the head can be monitored in one or more axes. These are altogether then emulated on the n-axis platform. Depending on the number of body parts and spatial motions thereof monitored, any correspondingly appropriate multi-axis positioning platform can be used. A platform based on those used for conventional flight-simulators but scaled down for a camera-sized application can be used. For instance, an even more scaled down version of the six degree of freedom principle demonstrated by the Polytec PI “Hexapod” can be used (Polytec PI, Inc., Suite 212, 23 Midstate Drive, Auburn, Mass. 01501 USA, the subsidiary of Physik Instruments (PI) GmbH &amp; Co., and Polytec GmbH, both of Polytec-Platz 5-7,76337 Waldbronn, Germany). 
   It will now be more fully realized from the foregoing, as mentioned above, that there will now be new opportunities for far more dynamic types of telepresence applications, including remote video monitoring, particularly on the Internet, and in ways heretofore never even contemplated. In particular, it can be foreseen that there will be extremely high demand for exciting, new telepresence applications. 
   As also mentioned above, these telepresence applications suffer from an underlying assumption borrowed from the art of “virtual reality” where the user is enabled to navigate within a virtual environment in a highly autonomous manner. The user takes command of the virtual environment and actively controls all of the responses of the reality engine according to monitored activity of the user. This has been shown extended to a wideband network in  FIG. 2 . This dedication of the tools needed to generate the remote presence for a single user is quite expensive. A way to meet the anticipated high demand in an efficient and economical manner will now be shown. 
   According to the present invention, the remote monitoring carried out under the control of a remote active viewer using an HMD/attitude sensor  56 ,  62  combination, such as in  FIG. 2 , can be used to control not only a camera/n-axis platform  88 ,  100 , but also one or more passive viewing platforms for use by one or more remote passive viewers. In other words, both “what” the passive viewers see, and the “attitude” in which they see same, are controlled by the active viewer. Further, for such embodiments, according to the teachings hereof, the passive viewing need not be contemporaneous with the image acquisition process, but may be delayed in time to any desired extent using a memory or other storage facility. 
   For instance,  FIG. 3  shows that one or more of the remote viewers may be passive viewers whose attitudinal head movements are not monitored at all but rather are instead mechanically guided to emulate the attitudinal head movements of the active viewer whose head movements are monitored by the attitude sensor  62  such as already shown along with the HMD  56  in  FIG. 2 , which is also shown again in  FIG. 3 . Such a passive apparatus  114  is shown in  FIG. 3  with a light source  115 , e. g., such as the type of display used for an HMD  116  (shown in  FIG. 4 ), mounted on a head guide  118  which may be an actuatable multi-axis platform which is in turn actuated by an actuator  120  under the control of an actuation signal on a line  112 . Several examples of such display devices for such passive use is described in more detail in copending application Ser. No. 08/794,122 filed Feb. 3, 1997, now U.S. Pat. No. 6,181,371, and which is hereby incorporated by reference. The actuation signal on the line  112  is provided by an interface  122  that receives a signal on a line  124  from the WISP  42 . An image signal is also provided on a line  126  from the interface  122  to the light source  115 . 
   As shown in further detail in  FIG. 4 , if the light source  115  is part of an HMD  116 , the is HMD may be optionally detachable along with the light source  115  from the head-guide  118  and, for that purpose, will also optionally include an attitude sensor  62   b  so that the HMD and light source while detached from the head guide may alternatively be used in a active way by the viewer as previously described in connection with  FIG. 3 . It should be realized that there need not be any HMD provided with the passive apparatus  114  and that the light source alone can be used with the head guide with or without the attitude sensor. If used with a sensor, the apparatus  114  could be built in the same way as the various devices shown in U.S. Pat. No. 5,436,638 except with actuators as well as sensors. For instance, the pivot  110  of  FIG. 1  or the assembly  770  of  FIG. 6  of Bolas et al could be actuated. It should also be realized, however, that such a light-source/head-guide combination can also be designed as a dual use active/passive display apparatus so the user can select to operate in either active or passive mode. The user will want to select active mode if the desired camera is not in use by anyone else. Or, if the desired camera is already in use, the user can select passive mode and the WISP  42  can then transmit the head attitude signals on the line  68  to both the n-axis camera platform  100  and to the apparatus  114  for actuating both the n-axis platform  100  and the apparatus  114  for emulating the attitudinal head motions of the user of the HMD  56 . 
   Considering the foregoing, the systems of  FIGS. 2-4  can be used in a communication network application such as, but not limited to, the internet. A user of one of the HMDs  56 ,  58 ,  60  can contact his internet service provider  42  using an internet browser and access the internet service provider  80  for gaining control of one of the cameras  90 ,  91 ,  92  for the purpose of remote viewing. These cameras can be located in different locations such as the factory, warehouse and loading dock of the prior art mentioned above in connection with  FIG. 1 . However, given the wide bandwidth capabilities now becoming available, the cameras could be located in places that would have wide appeal to the general public such as tourist sites, educational settings, entertainment performances, or the like. 
   A conventional display  128  responsive to a signal on a line  130  from an interface  132  can be used instead of the HMD  56  or the device such as shown in U.S. Pat. No. 5,436,638. An attitude sensor or a conventional input device such as a mouse, joystick or the like  134  can be used, or a sensor such as shown in U.S. Pat. No. 5,436,638, to provide an upstream control signal on a line  136  to the interface  132 . The interface  132  interchanges a bidirectional signal on a media line  138  with a wideband internet service provider  140  connected to the internet  76  by a line  142 . 
   The wideband internet service provider  80  could own and operate the remotely located cameras and provide internet access to the various active viewers of  FIG. 2  through a web page of the provider  80 . Or the provider  80  could allow other owners of such cameras or other reality engines to hookup and provide video services to the various active and/or passive users through his web page. Such a wideband internet service provider could become a provider of specialized video services such as remote tourism. A problem with such a remote tourist site is that the demand for active control of a given camera, such as located at Niagara Falls, could become very high. In that case, the web page of the WISP  80  can give the user intending to use a particular site a choice: active or passive. If the camera at the desired site is not presently in use, then the intending user can choose the active option with his input device and take control of the remote camera by means of one of the attitude sensors  62 ,  64 ,  66  or the control device  134  of  FIG. 2 . But if the camera at the desired site is presently in use, the apparatus  114  of  FIGS. 3  or  4  becomes very useful because the user can opt to be a passive viewer. In that case, the control signal provided for instance by the active user of the HMD  56  to the n-axis camera platform  100  also has another role, i. e., to control the n-axis actuator The actuator  120 , in response to the signal on the line  112 , causes the head guide to execute n-axis motions in emulation of the n-axis motions of the n-axis platform  100  executed in response to the signals on the line  94 . Both the control signals on the lines  112  and  94  are derived from the sensed signal on the line  68  from the head attitude sensor  62 . In the case of the remote camera, it is caused to execute attitudinal motions emulative of the commands of the remote user from the head attitude sensor  62 . In the case of the apparatus  114 , it is also caused to execute attitudinal motions emulative of the commands of the remote user from the head attitude sensor  62 . Moreover, the video signals provided by the camera  90  via the internet  76  are provided to both the HMD  56  for viewing by the active viewer and to the light source  115  of the apparatus  114  for viewing by the passive viewer. It should be realized that although the attitudinal command signals for controlling the actuator  120  have been described as coming from the sensor  62 , they could be sent first to the video server  82  for repackaging and sent to the apparatus  114  along with the video signals by the server  82 . 
     FIG. 5  shows a communications network  144  connected to a telepresence server  146  with a web server connected to a plurality of generalized reality engines  148 ,  149   a ,  149   b . The reality engine  148 , e.g., can be one or more “live” cameras on n-axis platforms or prerecorded “virtual reality” programs. A display  150  under the control of an active user is shown in  FIG. 5 , as described above. The active user can access a webpage of the telepresence server  146  and, if not being used, seize control of the reality engine as described above with the display  150 . Subsequent users who can each be at different geographic locations and who want to use the reality engine cannot be active users but can be passive users using displays  152 ,  154 ,  156 , . . . ,  158 . As an alternative to the display  150  under the control of an active user drawn from the general public, the operator of the telepresence server  146  can use the services of a professional local director using a display  160  actively or a professional remote director using a display  162  actively who accesses the server through the network. 
   It should be realized that the displays need not be the versatile active/passive displays described here. The displays  150 ,  160 ,  162  can be designed to be useable purely as active displays such as the display shown in U.S. Pat. No. 5,436,638 to Bolas et al. Likewise, the displays  152 ,  154 ,  156 , . . . ,  158  can be designed to be useable purely as passive displays such as the various displays shown in co-pending U.S. patent application Ser. No. 08/794,122 filed Feb. 3, 1997, now U.S. Pat. No. 6,181,371, or even the simple conventional monitor  128  of  FIG. 2 . However, selectable active/passive displays are preferred for the reasons explained above. 
   It should also be realized that the selectable mode (active/passive) display does not have to include a detachable helmet mounted display for use when the active mode is selected. For instance,  FIG. 6  shows a selectable mode (active/passive) device  163  wherein a display  164  is attached to a shaft  166  that is rotatable  168  about a vertical z-axis  170  in both modes. The user places his hands on hand grips  172 ,  174  and places his eyes on display viewports  176 ,  178 . The shaft  166  is rotatably mounted in a first platform part, e.g., a disc  180  and is driven in the passive mode by a yaw motor  182  that is fixed to the disc  180 . In the active mode, rotations about the z-axis are measured by a yaw sensor  184 . The disc  180  is rotatably mounted within a second platform part, e.g., an inner annulus  185  on a pair of pins  186 ,  188  in the inner annulus for rotating the about an x-axis  190 . One end of the pin  186  is fixed in the disc  180  while the other end is journaled in a bearing for being rotatably driven by pitch motor  192  fixed to or in the inner annulus. The pitch motor  192  drives one of the pins  186  as a drive shaft about the x-axis to pitch disc  180  and the display  164  forward or backward in the passive mode. A pitch sensor  194  mounted in or on the inner annulus  185  senses rotation of the disc  180  about the x-axis in the active mode while the pitch motor is inactive. One pin  196  is shown of a pair of pins fixed in the inner annulus but journaled on bearings in a third platform part, e.g., an outer annulus  198  for rotating the inner annulus about a y-axis  200 . A roll motor  202  is fixed on or in the outer annulus  198  and drives the pin  196  as a drive shaft to rotate the inner annulus about the y-axis in the passive mode. A roll sensor  204  is fixed in or on the outer annulus and senses rotation of the inner annulus about the y-axis in the active mode while the roll motor is inactive. It should be realized that the sensors can be used in the passive mode as well to provide feedback signals for controlling the motors in closed loop fashion. If not used in this way, the attitude of the display in passive mode can be controlled in open loop fashion. 
     FIG. 7  shows a screen  206  of a monitor  208  shown in  FIG. 8  connected to a signal processor  210  by a line  212  that drives the monitor. A keyboard  214  is connected to the processor by a line  216 . An intending user uses a mouse  218  connected by a line  220  to the processor to select, for example, one of the tourist sites shown in  FIG. 7 . The screen  206  shows nine available sites, most of which are inactive but two of which are “now active.” One of the inactive sites such as the Grand Canyon can be selected with the mouse and the user is then able to use the display  164  of  FIGS. 6 and 8  in an active way. In that case, the motors  182 ,  192 ,  202  are inactive while the sensors  184 ,  194 ,  204  are used to indicate the present yaw, pitch and roll, respectively, of the display  164  by providing a sensed yaw signal on a line  222 , a sensed pitch signal on a line  224 , and a sensed roll signal on a line  226 . The signal processor  210 , in response to the sensed signals on the lines  222 ,  224 ,  226 , provides an output signal on a line  228  to a modem  230  which in turn provides the sensed signals on a line  232  to the communications network  144  and on to the reality engine  148  of  FIG. 5  via the telepresence server  146 . The server sends the sensed yaw, pitch and roll signals to the reality engine such as a 3-axis camera platform such as the platform  100  of  FIG. 3  located at the Grand Canyon. A camera on the platform such as the camera  90  provides an image signal on the line  94  back to the communications network  144  and on to the display  164  through the signal processor  210 . In this way, the device  163  of  FIG. 8  is used like the display  150  used in active mode by an active user. 
   On the other hand, the user can instead use the mouse  218  to select one of the more popular sites that is already under active control indicated by “(now active)” such as Niagara Falls. In that case, the telepresence server  146  and reality engine  148  are responsive to the already active user&#39;s actions for causing images to be gathered from attitudes dictated by the active user and for providing the gathered images and the sensed yaw, pitch and roll signals to the device  163  for use in a passive way. In other words, the communications network  144  provides the gathered images and sensed yaw, pitch and roll signals from the device  150  used in an active way and provides them on the line  232  to the modem  230  which in turn provides them to the processor  210  for display on the display  164  and for controlling the yaw, pitch and roll motors by control signals on lines  234 ,  236 ,  238  for controlling the device  163  and hence the attitude of the display  164 . In this way, a camera and associated platform at a popular site can be used by more than one user although only one is active. The same principle applies to accessing any kind of popular reality engine (such as preprogrammed “virtual reality” scenarios) which might otherwise be inaccessible because of high demand. 
   Although the invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.