Encyclopedia of Computer Science and Technology

496 VoIPtank crews and even individual soldiers in the field (seemilitary applications of computers).Early simulators used “canned” graphics and could notrespond very smoothly to control inputs (such as a pilotmoving stick or rudder). Modern virtual reality, however,depends on the ability to smoothly and quickly generaterealistic 3D graphics. At first such graphics could only begenerated on powerful workstations such as those madeby Sun or Silicon Graphics. However, as anyone who hasrecently played a computer game or simulation knows,there has been great improvement in the graphics availableon ordinary desktop PCs since the mid-1990s.A variety of software and programming tools can beused to generate 3D worlds on a PC (see computer graphics).First released in 1995, a facility called VRML (VirtualReality Modeling Language) is now supported by manyWeb browsers. There are also programming extensions forJava (Java 3D).Modern computer games thus embody aspects of virtualreality in terms of graphics and responsiveness. But trueVR is generally considered to involve a near total immersion.Instead of a screen, a head-mounted display (HMD) isgenerally used to display the virtual world to the user whileshutting out environmental distractions. Typically, slightlydifferent images are presented to the left and right eyes tocreate a 3D stereo effect.The other half of the VR equation is the way in whichthe user interacts with the virtual objects. Head-trackingsensors are used to tell the system where the user is lookingso the graphics can be adjusted accordingly. Other sensorscan be placed in gloves worn by the user. The system canthus tell where the user’s hand is within the virtual world,and if the user “grasps” with the glove, the user’s hand inthe virtual world will grasp or otherwise interact with thevirtual object. More elaborate systems involve a full-bodysuit studded with sensors.To make interaction realistic, VR researchers have hadto study both the operation of human senses and that of theskeleton and muscles. For a truly realistic experience, theuser must be able to feel the resistance of objects (whichcan be implemented by a force-feedback system). Soundcan be handled easily, but as of yet not much has been donewith the senses of smell and taste.In designing a VR system, there are a number of importantconsiderations. Will the user be physically immersed(such as with an HMD), or, as in some military applications,will the user be seeing both a virtual and the actualphysical world? How important is graphic realism vs. realtimeresponsiveness? (Opting too much for computationallyintensive realism might cause unacceptable latency, or delaybetween a user action and the environment’s response.)ApplicationsBesides military training, currently the most viable applicationfor VR seems to be entertainment. VR techniqueshave been used to create immersive experiences in elaboratefacilities at venues such as Disneyland and UniversalStudios, and to some extent even in local arcades. VR that isaccompanied by convincing physical sensations has allowedfor the creation of a new generation of roller coasters that ifbuilt physically would be too expensive, too dangerous, oreven physically impossible.However, there are other significant emerging applicationsfor VR. When combined with telerobotic technology(see telepresence), VR techniques are already being usedto allow surgeons to perform operations in new ways. VRtechnology can also be used to make remote conferencingmore realistic and satisfactory for participants. Clearly thepotential uses for VR for education and training in manydifferent fields are endless. VR technology combined withrobotics could also be used to give disabled persons muchgreater ability to carry out the tasks of daily life.In the ultimate VR system, users will be networked andable to simultaneously experience the environment, interactingboth with it and one another. The technical resourcesand programming challenges are also much greater for suchapplications. The result, however, might well be the sortof environment depicted by science fiction writers such asWilliam Gibson (see cyberspace and cyber culture).Further ReadingKim, Gehard Jounghyun. Designing Virtual Reality Systems: TheStructured Approach. New York: Springer, 2005.McMenemy, Karen, and Stuart Ferguson. A Hitchhiker’s Guide toVirtual Reality. Wellesley, Mass.: A. K. Peters, 2007.Sherman, William R., and Alan B. Craig. Understanding VirtualReality: Interface, Application, and Design. San Francisco: MorganKaufman, 2003.Sturrock, Carrie. “Virtual Becomes Reality at Stanford.” SanFrancisco Chronicle, April 29, 2007, p. A1. Available online.URL: http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/04/29/MNGFPPGVPF1.DTL. Accessed August 23, 2007.Virtual Reality Resources. Available online. URL: http://vresources.org/. Accessed August 23, 2007.VoIP (voiceover Internet protocol)The basic idea of VoIP is simple: the Internet can carrypackets of any sort of data (see tcp/ip), which means it cancarry the digitized human voice as well, carrying ordinaryphone calls. There are several ways to do this:• a regular phone plus an adapter that connects to thecomputer and compresses and converts between regularanalog phone signals and the digital equivalent• a complete “IP phone” unit that includes all neededhardware and software—no computer needed, just anetwork connection, such as to a router• use of the computer’s own sound card and speakerswith a microphone, plus software (often free)Using that last option, VoIP service can be essentiallyfree, regardless of distance. However, one can only callsomeone who is currently connected to the Internet andalso has VoIP software.Alternatively, one can subscribe to a VoIP provider suchas Skype who also provides connectivity to the “plain oldtelephone service” (POTS). This allows calling anyone whohas an ordinary phone: The VoIP provider sends the call