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