虚拟实境设计

虛擬實境設計AShortIntroductionbyK.-P.BeierTerminologyTheterm'VirtualReality'(VR)wasinitiallycoinedbyJaronLanier,founderofVPLResearch(VisualProgrammingLanguage)(1989).Otherrelatedtermsinclude'ArtificialReality'(MyronKrueger,1970s),'Cyberspace'(WilliamGibson,1984),and,morerecently,'VirtualWorlds'and'VirtualEnvironments'(1990s).Today,'VirtualReality'isusedinavarietyofwaysandofteninaconfusingandmisleadingmanner.Originally,thetermreferredto'ImmersiveVirtualReality.'InimmersiveVR,theuserbecomesfullyimmersedinanartificial,three-dimensionalworldthatiscompletelygeneratedbyacomputer.Head-MountedDisplay(HMD)Thehead-mounteddisplay(HMD)wasthefirstdeviceprovidingitswearerwithanimmersiveexperience.EvansandSutherlanddemonstratedahead-mountedstereodisplayalreadyin1965.Ittookmorethen20yearsbeforeVPLResearchintroducedacommerciallyavailableHMD,thefamousEyePhonesystem(1989).AtypicalHMDhousestwominiaturedisplayscreensandanopticalsystemthatchannelstheimagesfromthescreenstotheeyes,thereby,presentingastereoviewofavirtualworld.Amotiontrackercontinuouslymeasuresthepositionandorientationoftheuser'sheadandallowstheimagegeneratingcomputertoadjustthescenerepresentationtothecurrentview.Asaresult,theviewercanlookaroundandwalkthroughthesurroundingvirtualenvironment.Toovercometheoftenuncomfortableintrusivenessofahead-mounteddisplay,alternativeconcepts(e.g.,BOOMandCAVE)forimmersiveviewingofvirtualenvironmentsweredeveloped.BOOMTheBOOM(BinocularOmni-OrientationMonitor)fromFakespaceisahead-coupledstereoscopicdisplaydevice.Screensandopticalsystemarehousedinaboxthatisattachedtoamulti-linkarm.Theuserlooksintotheboxthroughtwoholes,seesthevirtualworld,andcanguidetheboxtoanypositionwithintheoperationalvolumeofthedevice.Headtrackingisaccomplishedviasensorsinthelinksofthearmthatholdsthebox.CAVETheCAVE(CaveAutomaticVirtualEnvironment)wasdevelopedattheUniversityofIllinoisatChicagoandprovidestheillusionofimmersionbyprojectingstereoimagesonthewallsandfloorofaroom-sizedcube.SeveralpersonswearinglightweightstereoglassescanenterandwalkfreelyinsidetheCAVE.Aheadtrackingsystemcontinuouslyadjustthestereoprojectiontothecurrentpositionoftheleadingviewer.InputDevicesandotherSensualTechnologiesAvarietyofinputdeviceslikedatagloves,joysticks,and3DMouseallowtheusertonavigatethroughavirtualenvironmentandtointeractwithvirtualobjects.3Dsound,tactileandforcefeedbackdevices,voicerecognitionandothertechnologiesarebeingemployedtoenrichtheimmersiveexperienceandtocreatemoresensualizedinterfaces.CharacteristicsofImmersiveVRTheuniquecharacteristicsofimmersivevirtualrealitycanbesummarizedasfollows:•Head-referencedviewingprovidesanaturalinterfaceforthenavigationinthree-dimensionalspaceandallowsforlook-around,walk-around,andfly-throughcapabilitiesinvirtualenvironments.•Stereoscopicviewingenhancestheperceptionofdepthandthesenseofspace.•Thevirtualworldispresentedinfullscaleandrelatesproperlytothehumansize.2.CharacteristicsofImmersiveVRcontinue•Realisticinteractionswithvirtualobjectsviadatagloveandsimilardevicesallowformanipulation,operation,andcontrolofvirtualworlds.•Theconvincingillusionofbeingfullyimmersedinanartificialworldcanbeenhancedbyauditory,haptic,andothernon-visualtechnologies.NetworkedapplicationsallowforsharedvirtualenvironmentsSharedVirtualEnvironmentsIntheexampleillustrated,threenetworkedusersatdifferentlocations(anywhereintheworld)meetinthesamevirtualworldbyusingaBOOMdevice,aCAVEsystem,andaHead-MountedDisplay,respectively.Allusersseethesamevirtualenvironmentfromtheirrespectivepointsofview.Eachuserispresentedasavirtualhuman(avatar)totheotherparticipants.Theuserscanseeeachother,communicatedwitheachother,andinteractwiththevirtualworldasateam.Non-immersiveVRToday,theterm'VirtualReality'isalsousedforapplicationsthatarenotfullyimmersive.Theboundariesarebecomingblurred,butallvariationsofVRwillbeimportantinthefuture.Thisincludesmouse-controllednavigationthroughathree-dimensionalenvironmentonagraphicsmonitor,stereoviewingfromthemonitorviastereoglasses,stereoprojectionsystems,andothers.Apple'sQuickTimeVR,forexample,usesphotographsforthemodelingofthree-dimensionalworldsandprovidespseudolook-aroundandwalk-troughcapabilitiesonagraphicsmonitor.VRMLMostexcitingistheongoingdevelopmentofVRML(VirtualRealityModelingLanguage)ontheWorldWideWeb.InadditiontoHTML(HyperTextMarkupLanguage),thathasbecomeastandardauthoringtoolforthecreationofhomepages,VRMLprovidesthree-dimensionalworldswithintegratedhyperlinksontheWeb.Homepagesbecomehomespaces.TheviewingofVRMLmodelsviaaVRMLplug-inforWebbrowsersisusuallydoneonagraphicsmonitorundermouse-controland,therefore,notfullyimmersive.However,thesyntaxanddatastructureofVRMLprovideanexcellenttoolforthemodelingofthree-dimensionalworldsthatarefunctionalandinteractiveandthatcan,ultimately,betransferredintofullyimmersiveviewingsystems.ThecurrentversionVRML2.0hasbecomeaninternationalISO/IECstandardunderthenameVRML97.RenderingofEscher'sPenroseStaircase(modeledbyDigantaSaha):VRMLcontinueVR-relatedTechnologiesOtherVR-relatedtechnologiescombinevirtualandrealenvironments.Motion