Rapid Deployment of VRML Worlds for Military Planning Purposes
Lee A. Belfore, IIDepartment of Electrical and
Computer EngineeringOld Dominion UniversityNorfolk, VA 23529, U.S.A.
Alton ChavisACC/CEVP
129 Andrews St. Suite 102Langley AFB, VA 23665
Walt Baskin�
Sparta, Inc.3630 George Washington
Memorial PkwyYorktown, VA 23693
[email protected] Stevens
Loyola Enterprises303 Butler Farm Road, Suite 106
Hampton, VA [email protected]
Keywords: VRML, GIS, Rapid deployment, Terrain DataManagement
AbstractBroad disseminationof planning information presents
problemsto military plannersdue to the complexity of theinformation to be displayedand the unknown performancecapabilitiesof computingplatforms. The ubiquitousInter-netprovidesa solutionfor informationdelivery. In addition,theVirtual RealityModelingLanguage(VRML) supportstherepresentationof information both in traditional and novelways. Military planninginformationoften describesplacesin theworld whereamilitary operationis underwayor abaseis planned. Suchinformation includesof GIS information,andthe locationandplacementof variousstructures.In thispaper, wepresentanoverview of thearchitectureandthepro-cessfor creatingthesevirtual worlds. In particular, we willdiscussmethodsfor creatingandintegratingterraindata,im-agery, andotherfeaturesinto a virtual world. Fromaninter-active perspective, the worlds featurea numberof tools thataidin navigationandexploringtheworld, suchasmenus,andanimatedfly-throughs. In addition,we will discusssomeofthetools thathave beenintegratedinto thevariousworldstoenhancetheir utility. Throughanexample,we show how thevisualizationscanbe usedfor variousplanningapplicationsthroughthecontrolof featurevisibility.
INTRODUCTIONThe Internethas becomea medium for communicating
a rich variety of information not constrainedby traditional
1Work wasconductedwhile Walt Baskinwasemployed by Loyola En-terprises.
boundaries.The form in which the informationis presentedis quite novel when comparedto traditional delivery (i.e.paper/hard-copy) but theinformationprovidersarestill learn-ing how best to deliver the information and in what form.Furthermore,the delivery platform,web serversandclients,provideextraordinaryflexibly becausethey arealsoprogram-mingplatforms.Technologistsarecontinuingto developnewprogrammingplatformson which contentcanbe delivered.Web pagesinclude Javascriptprogrammingto increasethecapabilityand flexibility of the web pagepresentation.In-deed,as the technologyis applied, it evolvesas evidencedby the variety of platformsfor informationdelivery. In thiswork, we presentanapplicationthatincorporates3D contentdescribedin theVirtual RealityModelingLanguage(VRML)[1].
The successof a particularapproachcanbe measuredinterms of the value addedin its deployment. Virtual real-ity offersgreatpotentialfor delivering information. Indeed,compellingcontentcanbe createdin VRML with a moder-ateeffort. Furthermore,theeffort necessaryto producehighqualitycontenttypically requiresmoretime thanis available.Someapplicationsfocuson presentationof the contentonlyandcontainnoadditionalcollateralvalue.In contrast,wede-scribea methodfor rapid deploymentof compellingworldsthatprovidevaluebeyondtherendering.
This paperis dividedinto five sectionsincludinganintro-duction, an overview of the applicationarchitecture,a dis-cussionof how GIS datais integrated,a presentationof anexampledeploymentanda summary.
APPLICATION ARCHITECTUREThe applicationarchitectureconsistsof several compo-
nentsthat are integratedin variousways dependingon thespecificdeploymentdesired.Becausetheapplicationis GISbased,any object in the world must be referencedto a ge-ographiccoordinatesystem. Figure1 presentsa high levelview of thevirtual world architecturethatsupportsrapidde-ployment.Eachcomponentis discussedin moredetail.
World
Terrain/Imagery
Static Models
Dynamic Models
User Interface
Tools
Figure 1. Componentsof ApplicationArchitecturetoSupportRapidDeployment
Terrain and ImageryThebackdropsfor theworld consistof terrainandanim-
agethat is drapedover the terrain. In caseswherethe de-ploymentcoversa region that is largely flat, an imageon aplaneis sufficient. VRML provides two primitives (nodes)that canrepresentterrains:ElevationGridandIndexedFace-Set. TheElevationGridrequiresthat the terrainelevationbesampledon a rectangulargrid. The IndexedFaceSet,on theotherhand,providesa moregeneralcapabilitybut is some-whatmorecomplex. In caseswheretheterrainincludesbothflat andcomplex terrains,IndexedFaceSetscanbeemployedbecausedetail canbe concentratedwherenecessary. Issuesrelatedto managementof terrainandimageryaredescribedin thenext majorsection.
Static ModelsThestaticmodelsthatareintegratedinto theworld come
from a variety of sourcesandrequirements.Existing build-ingsandgroundcover canbe integratedasnecessaryto pro-ducethe desireddetail. In somecases,customconstructionof themodelsis necessaryto meettherequirementsfor apar-ticular case.In our work, severalmodelsmaybereusedwithlittle or no modificationin a broadclassof applications.Forexample,the rulesdefiningrunway approach-departuresur-facesaredefinedby standardparameters.Figure2 shows amodelusedto visualizerunwayapproach-departureandtran-
sitional surfaces. Models for buildings are frequentlycus-tomized,althoughin many casespresentablemodelscanbecreatedwith simplegeometriespaintedwith suitableimagesfor thebuilding sides.
Figure 2. Airport ObstacleAvoidanceSurfaces
Dynamic ModelsDynamicmodelshavethecapabilityof changingandmov-
ing within a world. Severalexampleshave beendeployedinvariousdemonstrationworlds.Themodelshave includedan-imatedviewpointsintendedto simulatewhata personmightseewhile traveling throughthe world. Componentswithintheworld canalsobeanimated,suchasaircrafthangardoorsopeningandclosing. Two significantexamplesof dynamicmodelsaredescribedin moredetail.
Tree Growth ModelModeling tree growth can provide the ability to do fu-
ture planning. In this example,a VRML EXTERNPROTOnodehasbeendevelopedto model treegrowth nearthe ap-proachendof a runway. In orderensureobstacleclearance,thetreesmustnot piercetheapproach-departuresurface.Tosupportthemodel,preciseinformationabouttreesis requiredandmustincludethe treelocation,height,groundelevation,andapproximateage. From this information,simplegeom-etry canbe usedto determinewhetherthe tree is a hazard.An imageshowing the tree growth model is shown in Fig-ure3. Treesgrowingnearanairportrunwayposeasignificantthreatto approachinganddepartingaircraft. In our model,we have includedthe ability to view treesasthey presentlyexist, andalsoextrapolatethegrowth patternsinto thefuture.Becausedifferentspeciesof treesgrow at differentrates,dif-ferentgrowth profilesareincluded.
Aircraft AnimationA componentof severalapplicationsis anaircraftanima-
tion. Theaircraftanimationhasbeendesignedto beaflexiblecomponentthatcanbeincludedin any application.Thisflex-ibility hasbeenachievedby packagingtheanimationcompo-nentsin a fully configurableVRML EXTERNPROTO node.
Figure 3. TreeGrowth Modeling
Theanimationnodeincludestheability to definethepathfortheaircraftflight, pitch, roll, andspeedchanges.In addition,theaircraftmodelcanbespecifiedat instantiationtime. Theanimationincludesthe specialcapabilitiesof changingtheaircraftpositionwith anexternalcontrol,changingthespeed,andincludinga text messagekeyedto differentsegmentsoftheanimation.Finally, in someapplicationsit is necessarytoexaggeratetheterrainelevationsby userrequest,requiringina collateralchangein the altitudescale. Figure4 shows animageillustratingsomeof thesecapabilities.
Figure 4. Aircraft Animation
User InterfaceTheuserinterfaceincludesseveralcomponentsthataid in
navigating througha world, interactingwith the world, andidentifyingimportantfeaturesandlocationswithin theworld.In severaldeployedworlds,a collectionof componentshavebeencreatedthatimprovethequality of theexperience.Sev-eralcomponentsof theuserinterfacearedescribedin thefol-lowing paragraphs.Dependingontherequirementsof thede-ployment,oneor all of thesecomponentscanbeintegrated.
MenuThe menu provides the user direct control over major
modes,appearanceandpropertiesof the world. The menu
maybeintegratedinto thevisualizationin oneof threeways.First, the menumay be visible only at a specific positionwithin thevisualization.Second,themenumaybe incorpo-rateddirectly within theworld asa head’sup display, alwaysfollowing theuser’savatar. Third, themenucanbeexternaltotheworld, residingin a framewithin thebrowser. Thechoiceof theapproachdependson theeffectdesired.
ModesCertaincomponentsof a world aresensitive to useractiv-
ity andcanresult in world modechangeseitherby sensingthe user’s locationor by detectingmouseeventsover sensi-tive componentswithin the world. The modechangesmayresultin differentoptionsthataremadeavailableor differentaspectsof thevisualizationappearing.
ViewpointsViewpointsareVRML nodesthatdefinecamerapositions.
Placingtheviewpointsat strategic pointsin theworld facili-tatestheability to extractusefulexperiencesfrom theworld.
DisplaysIn order to provide continual feedbackto the operator,
messagesareprovided to the userat varioustimes. In mostcases,thedisplayis integratedwith themenuin thehead’supdisplay. In addition,messagesareoccasionallydirectly lo-catedwith therelatedobject. For example,theaircraftflightanimationcan includea text scroll of preprogrammedmes-sagesthat occur at variouspoints in the animation. In ad-dition, using the tools describedabove, information canbegeneratedto appearin aconvenienthead’sup display
ToolsToolsintegratedin thevisualizationenhancethequalityof
thepresentationandtheusefulnessof thevirtual world.
Distance and Area ToolsThe distanceandareatools canbe usedto measurefea-
tureswithin the world. The distancetool enablesmeasure-mentbetweentwo pointson a terrainby calculatingthedis-tanceof a user’s mouseclick-dragon the terrain. The initialandfinal pointsappearconnectedby a line. Thedistanceap-pearseitheronthedistancetool geometryor canbepassedtoa text display. This tool canbeusedto verify thegeographicscalematchesthe world scale. An areatool hasalso beendevisedthatallows theoperatorto identify verticesof anen-closingpolygon,show the enclosedarea,andalsocalculatetheareawithin thearea.
Navigation ToolExploringa virtual world from a computerdisplaycanbe
somewhatdisorientingdueto factorsrelatedtheawkwardnessof the plug-in navigation controlsandthe limitations of the
display. A cuecanbeprovidedby displayinga thumbnailofthegeographywith a marker indicatingthecurrentlocation.
INTEGRATION OF GIS DATAGISdataprovidesthecontext for aparticularworld. Three
issuesmust be consideredwhen integrating GIS data intoVRML worlds. First, all solid modelsin a VRML world aretied to a threedimensionalCartesiancoordinatesystem.Sec-ond,properknowledgeof technologicalissuesimprovesthequalityof theVRML world experience.Third,VRML worldscannotdirectly handlethe large datasetstypical in terraindata.Theseissueshave beenaddressedby otherresearchersandarediscussedin moredetailbelow.
Coordinate SystemsBecauseVRML supportsonly Cartesiancoordinates,us-
ing other coordinatesystemsrequire projectionsonto theCartesiancoordinatesystems.Onemayuseprojectedinfor-mationin oneof two ways. First, theprojectionsareappliedprior to integrating within the VRML world. Indeed, thegenericexport tools provided with ArcInfo andERDAS donot export thegeospatialcoordinatetransforms.Eachof theVRML scenegraphobjectsmust be manually transformed(rotated,translated,scaled)in order to register correctly incoordinatespace.This is necessaryin thatvarioustools thathave beendeveloped(distancemeasuring,area,and futureplannedtools) requirea geospatialmetric relatedto SI mea-surementunits in order to properly function. Second,geo-coordinatescanbe usedin the VRML world, but convertedin script methodsfor proper appearance.The GeoVRMLgroup[2] providesgeneraltreatmentof geocoordinaterefer-encingandterrainimageryswapping.We havechosennot touseGeoVRMLbecauseourworldsaremorelimited in scopeenablingus to usesimpler programmingconstructsto en-hancetheexperienceandimprove performance.The sourceof theGISdatais from ESRIcompatibledataformats,DEMs,andetc.
Managing Technological Issues to View GISData
Certaintechnologicalissuesmustbecarefullymanagedtocreateawell behavedVRML world. Thesourcedatais takenfrom industry standardGIS tools suchas ArcInfo and ER-DAS. GIS toolsprovide theability to manipulateGIS infor-mationandalsoto limit thescopeof thedatafor integrationinto the world. Furthermore,thesetools have the ability toexport informationinto VRML. As notedabove,VRML usessingleprecisionnumbersbut GIS systemsusedoublepreci-sion,which mustbe taken into accountwhenthe datais ex-ported.Furthermore,matchingthesizesof imagerywith thecomputerarchitecturecanresultin improvedperformance.
Georeferencedcoordinatesrequiredoubleprecisionnum-
bersfor accuraterepresentation.VRML numbersprovide in-sufficient precisionto accuratelyrendergeoreferenceddata.We handlethis by defininganorigin in theworld beingcon-structedandthenusingall georeferencedcoordinatesrelativeto this new origin origin. As a result, the translatedcoor-dinatesretainsufficient precisionto accuratelyrepresenttheworld.
Imagery is usedas a “canvas” that gives context to theVRML objectsthat areplacedin the scenegraph,andpro-videsa way to embedinformationthat is useful to the user.Dueto thebandwidthlimitationspresentthroughoutthedis-tributednetwork environment,a processof tiling anddeci-mating the resolutionof the imageshasbeendevelopedtooptimizetransferof thescenegraphover thenetwork. Expe-riencehasshown that tiling the imagesin a
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is optimal, sincethis size tendsto be an ideal matchwithgraphicsandmemoryarchitectures.Imagesarealsoreducedin resolution,or decimated,in orderto reducethe file sizes.This decimationis conductedoutsidetheimmediateareasofinterest,andhelpsin performanceandnavigationthroughthescenegraphfor computerswith minimal graphicsmemory.Scriptshavebeendevelopedin ERDAS to automatethetilingprocess,however, imagedecimationis still largely accom-plishedusingmanualmethods.
Terrain Data
Terraindatais derivedfrom a varietyof sourcesincludingUSGSDEM, NIMA DTED, andterrainbyproductsof stere-opair imagery orthorectification. Terrain from USGS andNIMA Level 1 is provided with 90 Meter postingsandcanbeintegratedinto ascenegraphin oneof two ways.First, thedatacanbeincorporatedasaterraingrid, whichprovidesrel-atively high fidelity to theactualterrainin a largescalearea.Second,for smallerscaleareaswhich extendout over hun-dredsor thousandsof miles, the terrainmustbe “loosened”or resampledto reducethe numberof postings.In reducingthenumberof postings,navigationperformancethroughthescenegraphis enhanced.However, in reducingthe numberof postings,problemsmaybeintroducedin that featuresthatmay occurbetweenthe postingsmay be excluded. In navi-gatinga scenegraphcreatedfor a grid with regularpostings,any imagerydrapedover the grid appearsto be “synthetic”in that starkanglesandshadows appearfrom variousview-points. Another methodof modelingterrain is by using aTriangularIrregular Network (TIN) mesh. This hasthe ad-vantageof modelingthe terrain accordingto the slopeandaspectof the terrain, andmaintainsa greaterfidelity to theterrainfeatures.As slopeandaspectchange,smallertrianglesarecalculatedto representthe changesin the terrainandallfeaturesarerepresentedto the limits of the terraindata. Im-agerythat is texturemappedover a TIN hasa morerealisticandnaturalappearancewhennavigatingthescenegraph,and
shadowsappearassofter, smootherandnot synthetic.Scenegraphnavigation performanceusinga TIN is dependentonhow many TIN elementsareusedin theterrainmodel.Appli-cationssuchasLightwave3D, 3D StudioMAX havefeaturesthatcanremove TIN elementsto sparsetheTIN meshto thedegreedesired.
The world designermustdecidewhat information is vi-tal in any givensituationandcreateasuitablescenegraph.Inthesecases,mixing resolutionsfor differentpartsof theworldcanprovidea reasonableresult.Onemethodfor accomplish-ing this is theuseof quadtreesto subdivide theterrainbeingmodeled[3]. Additional resolutionlevelscanbeprovidedincritical focuspoints.Figure5 presentsascenegraphfor ater-rain. Quadtreetiles aremanagedby a level of detail(LOD)
Lower Resolution
Higher Resolution
Figure 5. QuadTreeStructureUsedFor SomeTerrainModels
primitive built into VRML. LOD nodesallow theimageres-olution to changeautomaticallyasa functionof theviewingavatar’sposition.An alternativeapproachis to tile theterrainfor aworld,andfor selectedtiles,providehigherresolutionasappropriate.Figure6 givesandexampleof integratedmixedresolution(1 and2 meter)imagery.
EXAMPLE DEPLOYMENTIn this section,anexampledeploymentis presented.The
visualizationshowsanexampledeploymentfor airbaseplan-ning. Several of the capabilitiesof the visualizationarede-scribedbelow. The virtual world democontainsmany as-pectsdescribedabove tunedto a specificdeployment. Fig-ure 7 shows the openingview of the airbase. The imageryincludesplannedmodificationsto anexisting. A specialper-spective can be gainedby an animationof a flying aircraftthatincludesa viewpoint. Figures8 and9, respectively showa viewpointson the approachandfrom a guardtower. As-pectsof theworld canhaveadditionalinformationaccessiblethroughanchorsthat give accessto web pages. Figure 10shows thehospitalaswell asa webpageassociatedwith thehospital.Any informationthatcanbeformatedanddisplayedasawebpagemaybeprovided.
(a)Original Image
(b) AreaMagnified
Figure 6. MixedResolutionImagery
Figure 8. Aircraft on Approach
SUMMARYIn this paper, we have outlinedan approachto construct
VRML demonstrationworldsrapidly. By appropriatederiva-tion and conversionof GIS information into VRML, com-pellingworldscanbecreatedthatpresentrealisticandusefulvisualizationsthat canbeemployed in military planningap-plications.Furthermore,sinceVRML is astandardizedInter-nettechnologyoperatingwithin browsersandplug-insavail-ableat no cost,the worlds canbe deployedeasilyandinex-
Figure 7. Airforce Basewith OverlayHighlightingPlannedModifications
Figure 9. View from GuardTower
pensively over theInternet.
REFERENCES[1] The Web3D Consortium, Incorporated,
“The Virtual Reality Modeling Language”,http://www.web3d.org/Specifications/VRML97/index.html,1998.
[2] Martin Reddy, Lee Iverson,andYvanG. Leclerc, “Un-der the hoodof GeoVRML 1.0”, in Proceedings of theFifth Symposium on the Virtual Reality Modeling Lan-guage VRML2000, Monterey, CA, February2000, pp.23–38.
Figure 10. HospitalandAssociatedInformation
[3] Martin Reddy, YvanLeclerc,LeeIverson,andNat Blet-ter, “TerraVisionII: Visualizingmassiveterraindatabasesin VRML”, IEEE Computer Graphics & Applications,vol. 19,no.2, pp.30–38,March/April 1999.
