Virtualrealityisasystemthatenablesoneormoreuserstomoveandreactinacomputersimulatedenvironment.Varioustypesofdevicesallowuserstosenseandmanipulatevirtualobjectsmuchastheywouldrealobjects[1].Thisnaturalstyleofinteractiongivesparticipantsthefeelingofbeingimmersedinthesimulatedworld.Virtualworldsarecreatedbymathematicalmodelsandcomputerprograms.
InterfaceDevices
Virtualrealitysimulationsdifferfromothercomputersimulationsinthattheyrequirespecialinterfacedevicesthattransmitthesights,sounds,andsensationsofthesimulatedworldtotheuser[2].Thesedevicesalsorecordandsendthespeechandmovementsoftheparticipantstothesimulationprogram.
Toseeinthevirtualworld,theuserwearsaheadmounteddisplay(HMD)withscreensdirectedateacheye.TheHMDalsocontainsapositiontrackertomonitorthelocationoftheuser'sheadandthedirectioninwhichtheuserislooking.Usingthisinformation,acomputerrecalculatesimagesofthevirtualworldaslightlydifferentviewforeacheyetomatchthedirectioninwhichtheuserislooking,anddisplaystheseimagesontheHMD.Thecomputermustgeneratethesenewviewsatleasttentimesasecondinordertopreventtheuser'sviewfromappearinghaltingandjerkyandfromlaggingbehindtheuser'smovements.Virtualworldscenesmustbekeptrelativelysimplesothatthecomputercanupdatethevisualimageryquicklyenough.Becauseofthesesimplificationsandothershortcomingsofcurrentvisualdisplaysandcomputergraphics,VRparticipantscaneasilydistinguishasimulationfromphysicalreality.
TheUserofVirtualReality
UsershearsoundsinthevirtualworldthroughearphonesintheHMD.TheinformationreportedbythepositiontrackerontheHMDcanalsobeusedtoupdateaudiosignals.Whenasoundsourceinvirtualspaceisnotdirectlyinfrontoforbehindtheuser,thecomputertransmitssoundstoarriveatoneearalittleearlierorlaterthanattheotherandtobealittlelouderorsofterandslightlydifferentinpitch.However,aswithvisualimagery[3],therearecurrentlyscientificandengineeringchallengesthatmustbeovercomeinordertosimulateaccuratelyallthesoundsheardinthephysicalworld.
DevelopmentandUses
Researchershavebeenworkingonvirtualrealitydevicesformanyyears.Inthe1960sRaymondGoertzatArgonneNationalLaboratory[4]inArgonne,Illinois,andIvanSutherlandattheMassachusettsInstituteofTechnology[5]inCambridge[6],Massachusetts,demonstratedearlyversionsofHMDs.Goertz,andlaterMichaelNollofBellLaboratories[7],alsodevelopedprototypeforcefeedbackdevices.Inrecentyears,virtualrealitydeviceshaveimproveddramaticallyastheresultofvarioustechnologicaladvances.Computersnowaremorepowerful,haveahighermemorycapacity,aresmaller,andcostlessthaninthepast.Thesedevelopments,alongwiththeadventofsmallliquidcrystaldisplays(LCDs)thatcanbeusedinHMDs,havemadeitpossibleforscientiststodevelopvirtualrealitysimulations.
Virtualrealityiscurrentlyusedtoexploreandmanipulateexperimentaldatainwaysthatwerenotpossiblebefore.TherapistsuseVRtotreatsufferersofchildabuseandpeoplewhoareafraidofheights.Musculardystrophypatientscanlearntouseawheelchairthroughvirtualreality.
Inthefuture,surgeonsmayuseVRtoplanandpracticeanoperationonavirtualpatientratherthanarealperson.Architectscouldtakeclientsonavirtualtourofanewhousebeforeitwasbuilt.VRcouldbeusedtotraintheoperatorsofaircraftandothercomplicatedmachinery.NetworkVRsimulationscouldenablepeopleinmanydifferentlocationstoparticipatetogetherinteleconferences,virtualsurgicaloperations,orsimulatedmilitarytrainingexercises.
VirtualRealityPrograms
FlightSimulator
Aflightsimulator[9]isacomputergeneratedrecreationoftheexperienceofflying.Sophisticatedflightsimulators,costinghundredsofthousands[10]ofdollars,canprovidepilottraining,simulatingemergencysituationswithoutputtinghumancrewsandplanesatrisk[11].Flightsimulatorsoftwarerunningonpersonalcomputerssimulatesflightinalessrealisticfashion;itprovidesentertainmentandpracticeinnavigationandinstrumentreading.
Aflightsimulatorisaperfectexampleofprogramsthatcreateavirtualreality(orcyberspace[12]),oracomputergenerated"reality"inwhichtheuserdoesnotmerelywatchbutisabletoactuallyparticipate.Theusersuppliesinputtothesystembypushingbuttonsormovingayokeorjoystick,andthecomputerusesrealworlddatatodeterminetheresultsofthoseactions.Forexample,iftheuserpullsbackontheflightsimulatorsyoke,thecomputertranslatestheactionaccordingtobuilt-inrulesderivedfromtheperformanceofarealairplane.Themonitorwillshowexactlywhatanairplane'sviewscreenwouldshowasitbeginstoclimb.Iftheusercontinuestoclimbwithoutincreasingthethrottle,the"virtualplane"willstall(aswouldarealplane)andthe"pilot"willlosecontrol.Thustheuser'sphysicalactionsareimmediatelyandrealisticallyreflectedonthecomputer'sdisplay.Forallintentsandpurposes[13],theuserisflying,thatis,the"plane"obeysthesamelawsofnature,hasthesamemechanicalcapabilities,andrespondstothesamecommandsasarealairplane.
Notes
[1]Varioustypes...astheywouldrealobjects.as在这里为连词，意为“如同”，引出方式状语从句，因实际情况并非如此，故从句用了虚拟语气；另因该从句的谓语动词与主句中不定式动词senseandmanipulate相同，所以也省略了。
[2]inthatthey...devicesthat:句中第一个that引出介词in的宾语从句，与in在一起表示原因；第二个that引出的是定语从句，修饰devices。
[3]aswithvisualimagery...as(challenges)withvisualimagery(thathavebeenovercome)：正像战胜视觉形象的挑战一样。
[4]ArgonneNationalLaboratory：阿贡国家实验室，美国核能及高能物理研究中心。该中心位于芝加哥附近，始建于1946年，现有职员约5,000人，拥有强脉冲中子源和质子加速器等先进设备。
[5]theMassachusettsInstituteofTechnology:庥省理工学院。
[6]Cambridge:坎布里奇市(旧译剑桥)，在美国麻省境内，是世界著名的教育和研究中心，哈佛大学、麻省理工学院及其他一些著名大学位于此地。
[8]perspective：事物相互关系的外观。
[9]aflightsimulator:飞行模拟器。
[10]hundredsofthousands:几十万。
[11]toput...atrisk：拿……去冒险。
[12]cyberspace:计算机控制空间。
[13]Forallintentsandpurposes：实际上，实质上。
ProperNames
RaymondGoertz雷蒙德·哥尔兹(人名)
IvanSutherland伊凡·苏萨兰(人名)
MichaelNoll迈克尔·诺尔(人名)
Argonne阿贡(地名)
Illinois(美国)伊利诺伊州
Cambridge坎布里奇(旧译“剑桥”，美国城市)
Massachusetts(美国)马萨诸塞州(旧译麻省)
第5题
第7题
A、VirtualReality
B、VirtualRock
C、VolumeRatio
D、VibrationReduction
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