A programming approach to the visual simulation of

AprogrammingapproachtothevisualsimulationofadisasterAlbertoPaoluzziDip.InformaticaeAutomazione,UniversitaRomaTreViadellaVascaNavale79,00146Roma,[e-mail]25,1999AbstractThreeyearsago,aterribledeagrationhappenedduringtheexcavationofasubwaygallerynearNeaples.Inthispaperwedescribethegeometricmodelingandthevisualsimulationofsomepossiblesettingsofthecatastrophicevent.ThegeometricmodelsandthevisualsimulationarecurrentlybeingdevelopedinPLaSM.BothanimationandrenderingareperformedbyanOpenInventorinterfacewhichplaysanimationdatageneratedbythePLaSMinterpreter.KeywordsGeometricmodeling,Designlanguage,Animation,Visualsimulation.1Introduction1.1EventdescriptionInthispaperweaimtodiscusstheguidelinesofavisualsimulationoftheterribleaccidentwhichhappenedinthedreadfuldayofJanuary23,1999atSecondiglianonearNeaples(Italy),infrontofthestreetnumber7of\LimitonediArzanoStreet.Insuchadayaterriblegasexplosiondeagredduringtheexcavationofasubwaygallerypassingatadepthof18metersunderLimitoneStreet.Theexplosioncausedthecollapseoftheterrainabovethefrontofthegalleryexcavation.Partofthefacingbuildingcollapsedtooandarunningcarfelldowntheholethatwasjustopeningintheterrain.Fivepeoplediedinthedeagration,bothinthefallencarandinthegallery.1.2SimulationaimsandmethodologyThevisualsimulationworkdescribedhereispartofananalysisandsimulationstudygrantedtoCERTIAResearchConsortium,basedatUniversityofRome\TorVergata,bythecompany1whichwasinchargeofthesubwaygalleryconstruction.Duetobothtimeandbudgetcon-straints,aswellastothehugeintrinsicdicultyofsuchawork,wedecidedfromthebeginningofneithertryinganyphysically-basedsimulationnoraveryrealisticcomputer-generatedanima-tionusingmovieseects.Conversely,wedecidedtoconcentrateourattentionontheassessmentandreproductionofcausallinksandtimedependenciesbetweensuchphenomenaofveryshortdurationliketheinatingofthegasinthegalleryfromabrokenpipe,thepropagationoftheexplosivewaveinthegallery,thetimerelationshipsbetweenthecollapsesofterrainandofthebuildingfront,etc.Inparticular,themaingoalofthevisualsimulationworkdescribedherewasthatofsim-ulatingtwoalternativesettingsdiscussedinthepreliminarycourt’sdebate,sotoobtainsomeobjectiveinformationaboutthefeasibilityoftwoquitedierenteventchains.Twosuchverydierentsettingswerehencestudied,whicharedescribedbyquitedierentnetworkmodelsofthecatastrophicevent.Bothsuchmodelsweregeneratedbyjustdierentlycombiningthearcs/subnetsassociatedtosimulationactors,soobtainingtwooverallsimulationnetworksofdierenttopology.Byusingsuchnetworksimulationmodelsitwassopossibletoanalyzeandtestforfeasibilitysomecontrastingeye-witnessreportsoftheevent.Thedivideandconquer1paradigmwasextensivelyusedingeometryandmotionmodelingofthedisaster.Inparticulartwoseparatescenes,ofundergroundandforegroundenvironments,respectively,wereimplemented,tobetopologicallyconnectedatexplosiontime.Severalactorsinbothsceneswerealsohierarchicallydecomposed.Themodelingofgeometryandmotionswasperformedsymbolically,i.e.byusinganappropriateprogramminglanguage,andwithoutanygraphicaluserinterface.Thisguaranteedthecompletereproducibilityofeachmodelingandanimationhypothesis,aswelltheeasygenerationandevaluationofalternativedisastersettings.1.3PapercontentsThepaperisorganizedasfollows.InSection2thehardwareandsoftwareenvironmentsusedinthisprojectaredescribed,includingtheimplementedextensionstothegeometricprogramminglanguagePLaSM.InSection3thesetofdevelopedgeometricmodelsisdiscussed,whichconstitutetheforegroundsceneandtheundergroundscene,aswellasthethesetofanimatedmodelslivinginsuchtwosettings.InSection4thehigh-leveldesignofthevisualsimulationisshortlydescribed,togetherwithadiscussionofthemaingoalofthesimulation,whichconsistedinderivingsomeobjectiveinformationaboutthefeasibilityoftwoquitedierenteventchains.InSection5themainmethodsusedinthegeometricmodelingofsceneactorsarerecalled.Inparticular,itisshortlydiscussedthedimension-independenttransniteblendingofmanifoldsinfunctionspaces,whichwasveryeasytoimplementinafunctionallanguagelikePLaSM.Alsosomeimplementationexamplesinsuchalanguagearegiven,includingthereparameterizationofcurvesandtheimplementationoftheplanarholonomicmotionofamobilesystemfromthecentroidtrajectory.IntheConclusionsectionbothprosandcontrasofthisapproacharecomparedandsomefurtherextensionsofthelanguageareoutlined.1Iwouldactuallyprefertosaydivideetimpera,accordingtothelatinoriginalsentence.22Modelingenvironment2.1HardwareandsoftwareThevisualsimulationprojectwastargetedforthetheSGI/IRIXcomputationalenvironment,butalsosomeApplePowerPCwithMacOS8.1andwintelmachineswithWindowsNTwereusedinthisproject,forgeometricprogrammingandmodeltestingandforvisualinterfaceprogramming,respectively.Awide-rangeexplorationofthemarketofvisualsimulationandanimationsoftwaretoolswasexecutedasarststepofthepreliminarydesignoftheproject.Severalverypowerfulmodelingandanimationtoolsweresocarefullytakenintoaccount.Theyarebrieydiscussedinthecompanionpaper[5].Theusingofcommercialanimationsoftwarewassoonexcluded,dependingonbothbudgetlimitsand(