Abstract Kinetic Visualization A Technique for Illustrating 3D Shape and Structure

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KineticVisualization

ATechniqueforIllustrating3DShapeandStructure

EricB.LumAleksanderStompelKwan-LiuMa

DepartmentofComputerScience

UniversityofCaliforniaatDavis

Abstract

Motionprovidesstrongvisualcuesfortheperceptionofshapeand

depth,asdemonstratedbycognitivescientistsandvisualartists.

Thispaperpresentsanovelvisualizationtechnique–kineticvisu-

alization–thatusesparticlesystemstoaddsupplementalmotion

cueswhichcanaidintheperceptionofshapeandspatialrelation-

shipsofstaticobjects.Basedonasetofrulesfollowingperceptual

andphysicalprinciples,particlesflowingoverthesurfaceofanob-

jectnotonlybringout,butalsoattractattentionto,essentialinfor-

mationontheshapeoftheobjectthatmightnotbereadilyvisible

withconventionalrenderingthatuseslightingandviewchanges.

Replacingstillimageswithanimationsinthisfashion,wedemon-

stratewithbothsurfaceandvolumetricmodelsintheaccompany-

ingvideosthatinmanycasestheresultingvisualizationseffectively

enhancetheperceptionofthree-dimensionalshapeandstructure.

Theresultsofapreliminaryuserstudythatwehaveconductedalso

showevidencethatthesupplementalmotioncueshelped.

CRCategories:I.3.3[ComputerGraphics]:Picture/Image

Generation—DisplayalgorithmsI.3.7[ComputerGraphics]:

Three-DimensionalGraphicsandRealism—Animation

Keywords:animation,visualperception,particlesystems,

scientificvisualization,volumerendering

1Introduction

Timevaryingsequencesofimagesarewidelyusedinvisualization

asameanstoprovideanextradimensionofinformationforpercep-

tiontooccur.Thisanimationmightbeassimpleasthechanging

ofcameraorobjectpositionsorcanincludeanimationsresulting

fromtimevaryingchangesinthedataitself.However,usingmo-

tionthatisindependentofchangesinviewingdirectionforcon-

veyingtheshapeinformationofstaticobjectshasbeenarather

unexploredarea.Inthispaper,wedescribeanewvisualization

technique,whichwecallkineticvisualization,creatinganimations

thatillustratetheshapeofastaticobjectinaperceptuallyintuitive

manner.

CIPIC&DepartmentofComputerScience,UniversityofCalifornia,OneShieldsAvenue,Davis95616,lume,stompel,ma

@cs.ucdavis.eduFigure1:AsingleframeofananimationshowingaPETscanofa

mousebrain.Themethoddescribedinthispaperusesthemotion

ofparticlestoillustrateshape.Assuch,astaticimageliketheone

showndoesnotdemonstratethetechnique.Thereaderisencour-

agedtowatchtheaccompanyingvideos.

Thisworkismotivatedbytheobservationthattheflowoffast

movingwateroverarock,adynamicflamefromanopenfire,or

evenaflockofbirdsexhibitmotionthatgivestheperceptionof

shape.Ourtechniqueisbuiltontheinspirationswereceivedfrom

kineticart[20],thestudiesdoneincognitivescience,specifically

onstructure-from-motionperception[1,15],theideasofparticle

systems[12],andtheworkofInterrante[8]onusingtextureto

conveytheshapeofoverlappingtransparentsurfaces.Itisunique

becauseweareabletoapplymotionasasupplementalcuetoen-

hanceperceptionofshapeandstructure,andbecausethemotionis

creatednotonlyaccordingtothecharacteristicsofthedatabutalso

usingasetofrulesbasedlooselyonphysicsandbiology.

Astaticimagefromananimationgeneratedusingourtechnique

isshowninFigure1.Becauseofthenatureofthetechniquespre-

sented,readersareadvisedtowatchtheaccompanyingvideosin

ordertofollowtheexposition.Acopyofthevideoscanalsobe

downloadedfrom:

http://www.cs.ucdavis.edu/˜ma/kinvis/

1.1VisualCues

Withtraditionalrenderingmethods,lightingprovidesvaluable

spatialcuesthatassistspatialperception.ConsideringLambertian

surfaces,theilluminationequation[4]accountingfordiffuselight

is:

whereistheresultingintensity,isthelightsource’sin-

tensity,isthediffuse-reflectioncoefficient,isthesurface

Figure2:Thekineticvisualizationtechniquewedescribeisnot

meanttobeareplacementforconventionalrenderingmethods.For

example,themovingparticlesontheleftareusedincombination

withtraditionalvolumerenderingtocreatethevisualizationonthe

right.Sinceourtechniqueusesmotiontoillustrateshape,neither

ofthesestillimageisrepresentativeofourtechnique.

normalandisthedirectiontothelightsource.Thedotproductin

thisequationhastheeffectoftransformingthethree-dimensional

surfacenormalintoaonedimensionlightintensityseenbythe

viewer.Theresultofthislossofdimensionalityistheambiguity

insurfaceorientationsincemultiplenormalorientationscanmap

tothesamelightintensity.Forexample,undersomeconditions

concaveandconvexshapescanhavesimilarappearances,despite

thesurfaceorientationsbeingentirelydifferent.

Thenormaldirectionandthussurfaceorientationcanbemade

lessambiguouswiththeadditionofspecularlighting.Phongil-

luminationaddsaterm,whereistheviewdirectionandisthereflectedlightdirection,whichhastheeffectofindicat-

ingshapeusingnotonlythenormalvector,butalsothederived

reflectancevector.Thisvectorisonceagaintransformedintoa

one-dimensionalquantitywithadot-productoperation.Byrotat-

inganobject,theviewercanbetterresolvetheshapeofanobject