《計(jì)算機(jī)專業(yè)英語》謝希仁第二版-第13章講義

ComputerEnglishChapter13VirtualReality

Keypoints:

usefultermsanddefinitionsofVirtualReality

Difficultpoints:

applicationsandfeaturesofVRMLRequirements:Conceptofvirtualreality2.ApplicationsofVRML3.DescribethefeaturesofVRML4.了解廣告文體的特點(diǎn)NewWords&Expressions:Virtualreality虛擬現(xiàn)實(shí) jerky顛簸的，急動(dòng)的，此處指圖像抖動(dòng)abuse吸毒，濫用 preventfrom阻止，妨礙infrontof在……前面 relayvt.vi.中繼，轉(zhuǎn)播haptica.觸覺的 stylusn.指示筆，觸針dystrophyn.營養(yǎng)失調(diào) teleconferencen.（遠(yuǎn)程）電信會(huì)議13.1VirtualRealityAbbreviations:LCD(Liquid-CrystalDisplay)液晶顯示HMD(Head-MountedDisplay)頭部安裝的顯示器

13.1VirtualRealityVirtualrealityisasystemthatenablesoneormoreuserstomoveandreactinacomputer-simulatedenvironment.Varioustypesofdevicesallowuserstosenseandmanipulatevirtualobjectsmuchastheywouldrealobjects1.Thisnaturalstyleofinteractiongivesparticipantsthefeelingofbeingimmersedinthesimulatedworld.Virtualworldsarecreatedbymathematicalmodelsandcomputerprograms.虛擬現(xiàn)實(shí)是一個(gè)能讓一個(gè)或多個(gè)用戶在計(jì)算機(jī)模擬環(huán)境下移動(dòng)和做出反應(yīng)的系統(tǒng)。各種設(shè)備讓用戶去感覺和操作虛擬物體，就像他們是真實(shí)物體一樣。這種自然的交互風(fēng)格讓參與者感到融入到模擬世界。虛擬世界是由數(shù)學(xué)模型和計(jì)算機(jī)程序創(chuàng)造的。13.1VirtualRealityVirtualrealitysimulationsdifferfromothercomputersimulationsinthattheyrequirespecialinterfacedevicesthattransmitthesights,sounds,andsensationsofthesimulatedworldtotheuser2.Thesedevicesalsorecordandsendthespeechandmovementsoftheparticipantstothesimulationprogram.虛擬現(xiàn)實(shí)模擬不同于其他要求特殊界面設(shè)備的計(jì)算機(jī)模擬，這些設(shè)備向用戶傳送模擬世界的視覺、聲音和感覺。這些設(shè)備還向模擬程序記錄和發(fā)送語音和參與者的運(yùn)動(dòng)。13.1VirtualRealityToseeinthevirtualworld,theuserwearsahead-mounteddisplay(HMD)withscreensdirectedateacheye.TheHMDalsocontainsapositiontrackertomonitorthelocationoftheuser’sheadandthedirectioninwhichtheuserislooking.Usingthisinformation,acomputerrecalculatesimagesofthevirtualworldaslightlydifferentviewforeacheyetomatchthedirectioninwhichtheuserislooking,anddisplaystheseimagesonthe(HMD).要觀看虛擬世界，用戶戴上一個(gè)頭部安裝的顯示器(HMD)，HMD上有在每只眼睛前表演的屏幕。HMD還包括一個(gè)監(jiān)視用戶頭部位置和觀看方向的跟蹤器。用這個(gè)信息，計(jì)算機(jī)重新計(jì)算每只眼睛稍微視覺差異的虛擬世界圖像，使它與用戶的觀察方向一致，同時(shí)在HMD上顯示這些圖像。13.1VirtualRealityThecomputermustgeneratethesenewviewsatleasttentimesasecondinordertopreventtheuser’sviewfromappearinghaltingandjerkyandfromlaggingbehindtheuser’smovements.Virtual-worldscenesmustbekeptrelativelysimplesothatthecomputercanupdatethevisualimageryquicklyenough.Becauseofthesesimplificationsandothershortcomingsofcurrentvisualdisplaysandcomputergraphics,VRparticipantscaneasilydistinguishasimulationfromphysicalreality.為了防止用戶視覺出現(xiàn)停止和抖動(dòng)以及滯后于用戶的運(yùn)動(dòng)，計(jì)算機(jī)必須以每秒至少十次的速度生成這些新圖像。虛擬世界的場(chǎng)景必須保持相對(duì)簡單，這樣計(jì)算機(jī)就能夠快的更新視覺圖像。由于這些簡單化及當(dāng)前視覺現(xiàn)實(shí)和計(jì)算機(jī)圖形的缺點(diǎn)，虛擬現(xiàn)實(shí)參與者能很容易從物理現(xiàn)實(shí)中區(qū)分出模擬事物。13.1VirtualRealityUsershearsoundsinthevirtualworldthroughearphonesintheHMD,theinformationreportedbythepositiontrackerontheHMDcanalsobeusedtoupdateaudiosignals.Whenasoundsourceinvirtualspaceisnotdirectlyinfrontoforbehindtheuser,thecomputertransmitssoundstoarriveatoneearalittleearlierorlaterthanattheotherandtobealittlelouderorsofterandslightlydifferentinpitch.However,aswithvisualimagery,therearecurrentlyscientificandengineeringchallengesthatmustbeovercomeinordertosimulateaccuratelyallthesoundsheardinthephysicalworld.在虛擬世界中，用戶通過HMD中的耳機(jī)聽到聲音，HMD中的位置跟蹤器報(bào)告的信息也能用來更換音頻信號(hào)。當(dāng)虛擬空間的聲源不直接在用戶的前方或后方，計(jì)算機(jī)傳達(dá)到某只耳朵的聲音比到另一只稍微早些或晚些。然而，正如視覺圖像，為了準(zhǔn)確模擬物理世界聽到的聲音，當(dāng)前科學(xué)和工程面臨必須克服的挑戰(zhàn)。13.1VirtualRealityThehapticinterface,whichrelays,thesenseoftouchandotherphysicalsensationsinthevirtualworld,istheleastdevelopedandperhapsthemostchallengingtocreate.Currently,withtheuseofagloveandpositiontracker,thecomputerlocatestheuser’shandandmeasuresfingermovements.Theusercanreachintothevirtualworldandhandleobjectsbutcannotactuallyfeelthem.中繼虛擬世界中觸覺和其他物理感覺的觸覺界面最不發(fā)達(dá)、而且大概要引起最大挑戰(zhàn)。當(dāng)前，由于使用了手套和位置跟蹤器，計(jì)算機(jī)使用戶的手定位，而且測(cè)量手指的運(yùn)動(dòng)。用戶能達(dá)到虛擬世界而且觸摸物體，但不能實(shí)際感覺到他們。13.1VirtualRealityItisparticularlydifficulttogeneratethesensationsthatarefeltwhenapersontapsahardsurface,picksupanobject,orrunsafingeracrossatexturedsurface.Tosimulatethesesensations,asetofcomputer-controlledmotorsfasterandmoreaccuratethananypresentlyavailablewouldhavetogenerateforcefeedbackbyphysicallypushingagainsttheuser.Anotherproblemisdetermininghowauserwouldwearthesemotorsandthewiringneededtocontrolthem.當(dāng)某人輕敲一個(gè)硬的表面，撿起一個(gè)物體、或手指拂過有織紋的表面時(shí)，特殊難產(chǎn)生出感覺到的感覺。要模擬這些感覺，一套比目前能得到的任何電機(jī)都快和精確的計(jì)算機(jī)控制的電機(jī)將必須由多用戶的實(shí)際推力產(chǎn)生反饋力。另一個(gè)問題是決定用戶如何穿戴這些電機(jī)和用于控制他們的電線。13.1VirtualRealityTouchsensationswouldalsohavetobesynchronizedwiththesightsandsoundsusersexperiencedintheirHMDs.Acurrentsolutiontothehapticchallengeistheuseofdesktopdevicesthatcanapplysmallforces,throughamechanicallinkage,toastylusheldintheuser’shand.Userscanfeelwhenthepointofthestylusencountersavirtualobject,andtheycandragthestylusacrossthesurfacetofeelitstextureandsurfacegeometry.觸覺還必須與用戶在他們HMD中經(jīng)歷的視覺和聲音同步。對(duì)觸覺挑戰(zhàn)的當(dāng)前解決辦法是使用可以施加小力的，通過一個(gè)機(jī)械連趕到用戶手中握著的觸針的臺(tái)式設(shè)備。當(dāng)觸針的針尖碰到一個(gè)虛擬物體，用戶能感覺到，而且他們能在表面上拖過觸針來感覺它的織紋和表面幾何形狀。13.1VirtualRealityInrecentyears,virtual-realitydeviceshaveimproveddramaticallyastheresultofvarioustechnologicaladvances.Computersnowaremorepowerful,haveahighermemorycapacity,aresmaller,andcostlessthaninpast.Thesedevelopments,alongwiththeadventofsmallliquid-crystaldisplays(LCDs)thatcanbeusedinHMDs,havemadeitpossibleforscientiststodevelopvirtual-realitysimulation.最近幾年，由于各種技術(shù)進(jìn)步的結(jié)果，虛擬現(xiàn)實(shí)設(shè)備已顯著改進(jìn)?，F(xiàn)在計(jì)算機(jī)功能更強(qiáng)大，存儲(chǔ)容量更高，比過去更小，價(jià)格更低。伴隨著可以用在HMD的小型液晶顯示器的到來，這些發(fā)展已經(jīng)使科學(xué)家開發(fā)虛擬現(xiàn)實(shí)模擬成為可能。13.1VirtualRealityVirtual-realityiscurrentlyusedtoexploreandmanipulateexperimentaldatainwaysthatwerenotpossiblebefore.TherapistsuseVRtotreatsufferersofchildabuseandpeoplewhoareafraidofheights.Musculardystrophypatientscanlearntouseawheelchairthroughvirtualreality.虛擬現(xiàn)實(shí)當(dāng)前用于探索和操縱實(shí)驗(yàn)數(shù)據(jù)，以前這種方式是不可能的。精神治療家用VR去治療兒童虐待的受害者和恐高癥患者。肌肉萎縮患者可以通過虛擬現(xiàn)實(shí)學(xué)習(xí)使用輪椅。13.1VirtualRealityInthefuture,surgeonsmayuseVRtoplanandpracticeanoperationonavirtualpatientratherthanarealperson.Architectscouldtakeclientsonavirtualtourofanewhousebeforeitwasbuilt.VRcouldbeusedtotraintheoperatorsofaircraftandothercomplicatedmachinery.NetworkVRsimulationscouldenablepeopleinmanydifferentlocationstoparticipatetogetherinteleconferences,virtualsurgicaloperations,orsimulatedmilitarytrainingexercises.將來，外科醫(yī)生可以用VR在虛擬病人身上計(jì)劃和實(shí)習(xí)手術(shù)，而不是在真人身上。在房子建設(shè)前，建筑師可以帶領(lǐng)客戶在新房中作虛擬旅行。VR可以用來訓(xùn)練戰(zhàn)斗機(jī)和其它復(fù)雜機(jī)械的操作者。網(wǎng)絡(luò)VR模擬能讓在許多不同地方的人一起參加電信會(huì)議、虛擬外科手術(shù)或模擬軍事演習(xí)。13.2RealWorkinVirtualRealityInthefuture,yourofficemaybelesslikeacubicleandmoreliketheHolodeckon“StarTrek”.Computerscientistsarealreadyexperimentingwiththetechnology,calledtele-immersion,thatwillallowustopeerintotheofficesofcolleagueshundredsofmilesawayandmakeusfeelasifwearesharingthesamephysicalspace.將來你的辦公室也許不像個(gè)小臥室而更像星際旅行的全息駕駛艙。計(jì)算機(jī)科學(xué)家已經(jīng)用叫做遠(yuǎn)程參與的技術(shù)進(jìn)行試驗(yàn)，這將我們窺見數(shù)百英里以外同事的辦公室，使我們感到就像我們?cè)诜窒硗晃锢砜臻g。13.2RealWorkinVirtualRealityComputerscientistsatseveraluniversitiesworkingonaprojectcalledtheNationalTele-ImmersionInitiativehavedemonstratedaprototypesystemthatenablesascientistworkingathisdeskinChapelHilltoseehisdistantcolleaguesontwoscreensmountedatrightanglestohisdesk.Itgiveshimtheillusionoflookingthroughwindowsintoofficesontheotherside.Andunlikevideoconferencing,tele-immersionprovideslife-size3-Dimages.致力于國家遠(yuǎn)程參與主動(dòng)性項(xiàng)目的幾所大學(xué)計(jì)算機(jī)科學(xué)家已展示了一個(gè)原始系統(tǒng)，讓在他的ChapelHall辦公室桌上工作的科學(xué)家能在他桌上直角安裝的兩個(gè)屏幕上看到他的遠(yuǎn)方同事。這給他一個(gè)錯(cuò)覺就像是從窗戶看到另一面的辦公室。與視頻會(huì)議不同，遠(yuǎn)程參與提供真實(shí)的立體圖像。13.2RealWorkinVirtualRealityIntheprototypesystem,eachresearcherissurroundedbyabankofdigitalcamerasthatmonitorhismovementsfromavarietyofangles.Theresearchersalsowearhead-mountedtrackinggearandpolarizedglassessimilartothoseusedtoview3-Dmovies.Whenaresearchermoveshishead,hisviewofhisco-workersshiftsaccordingly.Ifheleansforward,forexample,hiscolleaguesappearcloser,eventhoughtheyarehundredsofmilesaway.在原始系統(tǒng)中，每位研究人員被一群從不同角度監(jiān)視他的攝像機(jī)所包圍。研究人員還帶著頭部安裝的跟蹤裝置和類似那些用于觀看立體電影的偏振眼睛。當(dāng)研究人員移動(dòng)他的腦袋時(shí)，他的同事的圖像也相應(yīng)變動(dòng)。例如，如果它向前傾，他的同事就靠近，雖然他們相距數(shù)百英里。13.2RealWorkinVirtualRealityTomakethesystemwork,powerfulcomputersmustconvertdigitalimagesofeachparticipantintodatathatistransmittedviatheInternet,thenreconstructedintoimagesprojectedonthescreens.Sofar,themovementisjerkybecausetoday’scomputerscannottransmitdatafastenough.要使系統(tǒng)工作，強(qiáng)大的計(jì)算機(jī)必須把每個(gè)參與者圖像轉(zhuǎn)換通過因特網(wǎng)傳輸?shù)臄?shù)據(jù)，然后重新還原或投射在屏幕上的圖像。到目前為止，因?yàn)楝F(xiàn)在的計(jì)算機(jī)不能足夠快地傳送數(shù)據(jù)，運(yùn)動(dòng)還是抖動(dòng)的。13.2RealWorkinVirtualRealityThescientistshopethattele-immersionwillopenupahostofotherapplications:Forexample,patientsinruralareascould“visit”medicalspecialistsinfarawaycities.科學(xué)家們希望遠(yuǎn)程參與將通向許多其它的應(yīng)用，例如，農(nóng)村的患者可以“瞧”遠(yuǎn)在城市的醫(yī)學(xué)專家。NewWords&Expressions:interactive交互的 intranetn.企業(yè)內(nèi)部互聯(lián)網(wǎng)integrate使成整體，結(jié)合

visualizationn.可視化presentationn.演示 virtualadj.虛擬的criteria準(zhǔn)則 authorabilityn.創(chuàng)作性compose組成，寫作，排字

re-usabilityn.可重用性extensibility可擴(kuò)展性

explicitly明白地，明確地platform平臺(tái)

arbitrarily武斷地，任意地static靜態(tài)的 animated動(dòng)畫的，活生生的dynamic動(dòng)態(tài)的 hyperlink超級(jí)聯(lián)接authorv.制作 available可利用的registration注冊(cè)，登記 community團(tuán)體，公用interoperable能共同使用的 extensionn.延長，范圍scope范圍 specification規(guī)范，說明書13.3AboutVRML

NewWords&Expressions:conceptually概念地

aural聽覺的modify更改，修改 mechanisms機(jī)制primary原始的

composition合成法，排版encapsulation封裝 semantic語義resolution分辨率 latitude緯度，范圍，地區(qū)interpretation解釋，闡明 mouse鼠標(biāo)implicitly含蓄地，暗中地 coordinate坐標(biāo)recursively遞歸地，回歸地 sphere球體

reference提及，參考書目 enclose放入，封閉，包裝hierarchical分層的，層次的 spatialadj.空間的accumulation積聚，積累 dissipatev.使消失，失去intractable難處理的 compact緊湊的，簡潔的syntaxn.語法13.3AboutVRML

13.3AboutVRML

Abbreviations:VRML(TheVirtualRealityModelingLanguage)虛擬現(xiàn)實(shí)建模語言API(applicationprogrammerinterface)應(yīng)用程序界面TheVirtualRealityModelingLanguage(VRML)isafileformatfordescribinginteractive3Dobjectsandworlds.VRMLisdesignedtobeusedontheInternet,intranets,andlocalclientsystems.VRMLisalsointendedtobeauniversalinterchangeformatforintegrated3Dgraphicsandmultimedia.VRMLmaybeusedinavarietyofapplicationareassuchasengineeringandscientificvisualization,multimediapresentations,entertainmentandeducationaltitles,webpages,andsharedvirtualworlds.虛擬現(xiàn)實(shí)建模語言(VRML)是一種描述交互式三維對(duì)象及客觀世界的文件格式。VRML用于Internet、Intranet和局域客戶系統(tǒng)。VRML也是組合三維圖形和多媒體的通用轉(zhuǎn)換格式。VRML的應(yīng)用領(lǐng)域很廣，包括工程、科學(xué)可視化、多媒體演示、娛樂教育、Web頁面和共享虛擬世界等方面。13.3AboutVRML

13.3.1DesignCriteriaVRMLhasbeendesignedtofulfillthefollowingrequirements:

Authorability

Enablethedevelopmentofcomputerprogramscapableofcreating,editing,andmaintainingVRMLfiles,aswellasautomatictranslationprogramsforconvertingothercommonlyused3DfileformatsintoVRMLfiles.13.2.1設(shè)計(jì)標(biāo)準(zhǔn)VRML需要滿足如下要求：創(chuàng)作性使得應(yīng)用程序能夠建立、編輯、保存VRML文件，也是一個(gè)自動(dòng)翻譯程序，能夠?qū)⑼ǔＪ褂玫?D文件格式轉(zhuǎn)換成VRML文件。13.3AboutVRML

Composability

Providetheabilitytouseandcombinedynamic3DobjectswithinaVRMLworldandthusallowre-usability.ExtensibilityProvidetheabilitytoaddnewobjecttypesnotexplicitlydefinedinVRML.重構(gòu)性能夠在VRML環(huán)境中使用和組合動(dòng)態(tài)3D對(duì)象，并允許重用。擴(kuò)展性能夠加入在VRML中沒有明確定義的新的對(duì)象類型。13.3AboutVRML

Implementability

Capableofimplementationonawiderangeofsystems.PerformanceEmphasizescalable,interactiveperformanceonawidevarietyofcomputingplatforms.ScalabilityEnablearbitrarilylargedynamic3Dworlds.適用性能夠在各種系統(tǒng)中使用。性能在各種不同的計(jì)算機(jī)平臺(tái)上強(qiáng)調(diào)可擴(kuò)展的、交互的性能?？蓴U(kuò)展性適于任意大的動(dòng)態(tài)三維世界。13.3AboutVRML

13.3.2CharacteristicsofVRMLVRMLiscapableofrepresentingstaticandanimateddynamic3Dandmultimediaobjectswithhyperlinkstoothermediasuchastext,sounds,movies,andimages[1].VRMLbrowsers,aswellasauthoringtoolsforthecreationofVRMLfiles,arewidelyavailableformanydifferentplatforms.VRML的特性VRML能表示靜態(tài)及動(dòng)態(tài)的三維和多媒體對(duì)象，并通過超鏈接連到諸如文本、聲音、電影及圖像等其它媒體。VRML瀏覽器，同制作VRML文件的制作工具一樣，廣泛應(yīng)用于許多不同的平臺(tái)上。13.3AboutVRML

VRMLsupportsanextensibilitymodelthatallowsnewdynamic3Dobjectstobedefinedandaregistrationprocessthatallowsapplicationcommunitiestodevelopinteroperableextensionstothebasestandard.TherearemappingsbetweenVRMLobjectsandcommonlyused3Dapplicationprogrammerinterface(API)features.VRML支持?jǐn)U展模式，即允許創(chuàng)建新的3維動(dòng)態(tài)對(duì)象，并允許應(yīng)用程序組開發(fā)在基礎(chǔ)模式上加以擴(kuò)展的可共同操作的文件。在VRML對(duì)象和通常使用的應(yīng)用程序接口特性間有相應(yīng)的映射。13.3AboutVRML

13.3.3ScopeTheVRMLspecificationdefinesafileformatthatintegrates3Dgraphicsandmultimedia.Conceptually,eachVRMLfileisa3Dtime-basedspacethatcontainsgraphicandauralobjectsthatcanbedynamicallymodifiedthroughavarietyofmechanisms.VRMLdefinesaprimarysetofobjectsandmechanismsthatencouragecomposition,encapsulation,andextension.

VRML能表示靜態(tài)及動(dòng)態(tài)的三維和多媒體對(duì)象，并通過超鏈接連到諸如文本、聲音、電影及圖像等其它媒體。VRML瀏覽器，同制作VRML文件的制作工具一樣，廣泛應(yīng)用于許多不同的平臺(tái)上。

13.3AboutVRML

ThesemanticsofVRMLdescribeanabstractfunctionalbehavioroftime-based,interactive3D,multimediaworlds.VRMLdoesnotdefinephysicaldevicesoranyotherimplementation-dependentconcepts(e.g.,screenresolutionandinputdevices).VRMLisintendedforawidevarietyofdevicesandapplications,andprovideswidelatitudeininterpretationandimplementationofthefunctionality.Forexample,VRMLdoesnotassumetheexistenceofamouseor2Ddisplaydevice.

VRML的語義描述了一個(gè)抽象的時(shí)間依賴的、交互性3維的功能行為。VRML并不定義一個(gè)具體的設(shè)備或任何依賴它實(shí)現(xiàn)的概念（比如：屏幕分辨率和輸入設(shè)備）。VRML適用于大量的設(shè)備和應(yīng)用程序，并且提供了一個(gè)對(duì)功能加以解釋和實(shí)現(xiàn)的廣泛空間。比如：VRML并不認(rèn)為有鼠標(biāo)或2維顯示設(shè)備的存在。

13.3AboutVRML

13.3.4EachVRMLfile:1.implicitlyestablishesaworldcoordinatespaceforallobjectsdefinedinthefile,aswellasallobjectsrecursivelyincludedbythefile;2.explicitlydefinesandcomposesasetof3Dandmultimediaobjects;3.canspecifyhyperlinkstootherfilesandapplications;4.candefineobjectbehaviors.1.為文件中的所有對(duì)象建立了一個(gè)世界坐標(biāo)系，也包括在文件中遞歸包含的所有對(duì)象。2.明確定義并構(gòu)成一個(gè)3D和多媒體對(duì)象的集合。3.可定義超鏈接與其它文件和應(yīng)用程序相連。4.可定義對(duì)象的行為。13.3AboutVRML

AnimportantcharacteristicofVRMLfilesistheabilitytocomposefilestogetherthroughinclusionandtorelatefilestogetherthroughhyperlinking.Forexample,considerthefileearth.wrlwhichspecifiesaworldthatcontainsasphererepresentingtheearth.ThisfilemayalsocontainreferencestoavarietyofotherVRMLfilesrepresentingcitiesontheearth(e.g.,fileparis.wrl).Theenclosingfile,earth.wrl,definesthecoordinatesystemthatallthecitiesresidein.Eachcityfiledefinestheworldcoordinatesystemthatthecityresidesinbutthatbecomesalocalcoordinatesystemwhencontainedbytheearthfile.VRML文件的一個(gè)重要特性是能夠通過包含和超鏈接將文件組合在一起。比如：文件earth.wrl,定義了一個(gè)表示地球的球體，它也可以包含指向表示地球上其它城市的文件的索引（如：文件paris.wrl）。外封文件：earth.wrl定義了所有城市所處的坐標(biāo)系。每一個(gè)城市文件定義了城市所在的世界坐標(biāo)系系統(tǒng)，但是當(dāng)包含在文件earth.wrl中時(shí)，就變成了局部坐標(biāo)系統(tǒng)。13.3AboutVRML

Hierarchicalfileinclusionenablesthecreationofarbitrarilylarge,dynamicworlds.Therefore,VRMLensuresthateachfileiscompletelydescribedbytheobjectsandfilescontainedwithinitandthattheeffectsofeachfilearestrictlyscopedbythefileandthespatiallimitsoftheobjectsdefinedinthefile.Otherwise,theaccumulationoffilesintolargerworldswouldproduceunscalableresults(aseachaddedworldproducesglobaleffectsonallotherworlds).文件的層次關(guān)系允許創(chuàng)建任意大的、動(dòng)態(tài)的世界。因此，VRML確保了每個(gè)文件由包含在其中的對(duì)象和文件完全描述，并且每個(gè)文件的效果由文件和文件中定義的對(duì)象的空間范圍嚴(yán)格限定。否則的話，由很多文件定義一個(gè)大的世界坐標(biāo)系將是不可擴(kuò)展的（因?yàn)槊恳粋€(gè)加入的坐標(biāo)會(huì)對(duì)其它坐標(biāo)產(chǎn)生一個(gè)全局的影響）。13.3AboutVRML

Forexample,lightsourceshavethepotentialofglobaleffectsincelightenergytheoreticallydoesnotdissipatetozero.And,iftheearthfilecontains100cityfileseachcontaining100lightseachaffectingallobjectsintheworld,thelightingcalculationswouldquicklybecomeintractable.Therefore,inordertopreventglobaleffects,lightsourceobjectsarescopedbyeitheramaximumradiusorbylocationwithinthefile.比如，因?yàn)楣饽茉诶碚撋喜粫?huì)消失為0，光源對(duì)整體效果有潛在的影響。另外，如果地球文件包含100個(gè)城市文件，每個(gè)城市文件包含100個(gè)光源，會(huì)影響到整體坐標(biāo)系的每個(gè)對(duì)象。光源的疊加將難于快速解決。因此，為了避免影響全局效果，光源對(duì)象或者由最大半徑或者由文件內(nèi)的一個(gè)區(qū)域限定。13.3AboutVRML

AnotheressentialcharacteristicofVRMListhatitisintendedtobeusedinadistributedenvironmentsuchastheWorldWideWeb.Therearevariousobjectsandmechanismsbuiltintothelanguagethatsupportmultipledistributedfiles,including:5.in-liningofotherVRMLfiles;6.hyperlinkingtootherfiles;7.usingestablishedInternetstandardsforotherfileformats;8.definingacompactsyntax

VRML的另一基本特性是適用于分布式環(huán)境，如環(huán)球網(wǎng)。在語言內(nèi)有不同的對(duì)象和固定機(jī)制支持多個(gè)分布式文件，包括：5.與其它VRML文件的鏈接；6.與其它類型文件的超鏈接；7.對(duì)其它格式文件使用確定的Internet標(biāo)準(zhǔn)；8.定義一個(gè)簡潔的語法。

13.3AboutVRML

一、個(gè)人簡歷個(gè)人簡歷（resume/curriculumvitae）是升學(xué)、求職過程中的重要文件。英文個(gè)人簡歷的格式比較固定，一般應(yīng)包括個(gè)人信息、聯(lián)系地址、求職愿望、學(xué)歷、工作經(jīng)歷、證明人等部分,也可以根據(jù)具體情況，適當(dāng)增加有關(guān)條目。內(nèi)容的安排要求清晰易讀、層次分明，學(xué)歷和工作經(jīng)歷一般可從最近開始，逐漸向后追述。從語言方面來看，個(gè)人簡歷多以名詞詞組為主，也可以使用動(dòng)詞詞組，但是要求結(jié)構(gòu)整齊對(duì)稱。以下是某位學(xué)生的個(gè)人簡歷，他申請(qǐng)的工作職位是某計(jì)算機(jī)公司的售后服務(wù)技術(shù)員。一般來說，他還需另外撰寫一份求職信，介紹一下本人的基本情況、特長及對(duì)該公司業(yè)務(wù)的熟悉程度，同時(shí)重申個(gè)人的工作愿望，并提出面試請(qǐng)求。求職英語簡介一、個(gè)人簡歷ResumePersonaldetails

Name:LiJian Age:20 DateofBirth:May21,1981 MaritalStatus:single Address:36YanshanStreet,Jinan,Shandong250014,P.R.China TelE-mail:lijian@Positionappliedfor After-saleServiceTechnician求職英語簡介一、個(gè)人簡歷Education：

September1995topresent ShandongInstituteofElectronicTechnology, MajorinAppliedComputingwithspecialinterestin networking&websiteimplementation. Coursestaken:CProgramming,SoftwareEngineering, VisualFoxpro,MicrosfotOffice,DataStructuresinC, EnglishforComputing,ComputerNetworks, InternetApplication,etc. September1992toJuly1995

JinanNo.14MiddleSchool,Jinan,Shandong. Monitorofclass,outstandinginmath&physics.求職英語簡介一、個(gè)人簡歷Workexperience：

Summer1998 Company:ABCComputerCorp. Post:SalesPromotion Responsibility:organizingproductexhibitiontours& marketsurvey. Summer1997 Company:HopeCo.,Ltd Post:SystemIntegration Responsibility:assemblingPCsaccordingtocustomer requirements;fixinghardwareproblems;on-the-spotinstallation&testing. Summer,1996 Company:EastsoftCo.,Ltd Post:Reception Responsibility:understandingcustomerneeds;explainingEastsoft products&services;highlightingEastsoftafter-saleservice.求職英語簡介一、個(gè)人簡歷Honors

TopPrizeinHomepageDesignContest,1998.OtherInformation

FluentinEnglishwithaTOEFLscoreof590.Ref