Integrating Dynamic Deformations into Interactive Volume

Non-linear geometric deformation (or warping) is a useful tool for working with volumes. Unfortunately, the computational expense of performing the resampling needed to implement volume deformation has precluded its use in interactive applications. In this

Eurographics/IEEE-VGTCSymposiumonVisualization(2006)ThomasErtl,KenJoy,andBeatrizSantos(Editors)

IntegratingDynamicDeformationsintoInteractiveVolume

Visualization

TomBrunet

K.EvanNowak

MichaelGleicher

DepartmentofComputerSciencesUniversityofWisconsin,Madison

Abstract

Non-lineargeometricdeformation(orwarping)isausefultoolforworkingwithvolumes.Unfortunately,thecom-putationalexpenseofperformingtheresamplingneededtoimplementvolumedeformationhasprecludeditsuseininteractiveapplications.Inthispaper,weshowhownon-lineardeformationscanbeintegratedintointeractivevolumevisualizationallowingfordynamicdeformationstobeusedalongwithinteractiveviewing,exploration,andmanipulationtools.Wedescribehowhardwareassistedvolumerenderingcanbeadaptedtoresamplevolumedeformations,leveragingprogrammableshaderstocomputedeformationsandthelocalcoordinatetransforma-tionsrequiredforshadingeffects.Wedescribehowvolumeinteractiontechniques,suchasraypickingandplaneslicing,canbeusedinconcertwithourdeformationmethods.Ourmethodsextendtosimultaneousdisplayofmultiplevolumesenablingcomparisons.Wedemonstratedynamicvolumedeformationatinteractiveratesoncommodityhardwareforinteractivedeformationcontrol,animateddeformations,andvolumewidgets.CategoriesandSubjectDescriptors(accordingtoACMCCS):I.3[ComputerGraphics]:

1.Introduction

3DScalarField(e.g.Volume)dataisimportantandcom-moninscienceandmedicine.Applyingnon-lineargeomet-rictransformationstovolumedataisavaluablepartofitsuse,allowingforthecorrectionofimagingdeformations,alignmentofdifferentobjects,andmodellingforanimation.Unfortunately,applyingdeformationstovolumesrequiresa3Dresamplingoperationthatiscomputationallyexpensive.Tointeractivelyvisualizeadeformedvolume,thedeforma-tionsandresamplingaretypicallyprecomputed,precludingdynamicdeformations.Applicationswherethedeformationschangeatinteractiverates,suchasinteractivenon-linearreg-istration,real-timevolumeanimation,andanimateddefor-mationinteractiontechniqueshavebeenrestricted.Thispaperprovidesmethodsthatintegratespatialtrans-formationsintoarangeofinteractivevolumevisualizationtools.Theprinciplecontributionistoshowtheeffectivenessofprogrammablegraphicshardwarefortherenderingofde-formedvolumesandforencapsulatingthedeformation.De-formationsarecomputedper-pixelinfragmentshaders.Wewillshowthatplacingthedeformationcomputationinthis

cTheEurographicsAssociation2006.

innermostloopofrenderinghasseveralbene tsandcanbe

doneatinteractiverates.

Thebasicrenderingofdeformedvolumesusingfragmentshadersisstraightforward,modulosomeissueswewillad-dress.Akeyadvantageoftheapproach,however,ishowthedeformationcanbeencapsulatedintheshader,makingiteasytosupportarangeoftoolsthataredesirableininterac-tivevolumevisualizationsuchasarbitraryslicing.Wealsocontributeanoveltechniqueforperformingpickingbyraycastingintothedeformedvolumes.

Previouswork,suchas[FHSR96]and[RSSSG01],hasusedgraphicshardwaretoprovideinteractivedisplayofdeformedvolumes.However,ournewmethodprovidesagreaterrangeofvolumevisualizationtoolsincludingstyl-izedshading,slicingandprobing.Otherpriorwork,suchas[GTB03]hasshowntheusefulnessofdynamicdeforma-tionstoprovideinteractiontechniques,butprovidesalim-itedimplementation.Ourapproachenablestheintegrationofthesemethodswithothervolumetools.

Followingadiscussionofrelevantrelatedwork,wede-scribehowvolumedeformationsarerealizedaspartofthegraphics-hardware-basedvolumevisualizationshadingpro-

Non-linear geometric deformation (or warping) is a useful tool for working with volumes. Unfortunately, the computational expense of performing the resampling needed to implement volume deformation has precluded its use in interactive applications. In this

TomBrunet&K.EvanNowak&MichaelGleicher/IntegratingDynamicDeformationsintoInteractiveVolume

Visualization

Figure1:VisualizationofanMRIofamousetorso.Theoriginalvolume(left)istoneshaded.(right)VolumedeformedusingaHierarchicalB-Spline.Redcirclesdenotesourcepoints,andbluecirclesdenotetargetpoints.cess.Wespeci callyaddresstheissuesofrepresentingthedeformationfunctionsinfragmentprogramsandevaluat-ingthegradientsrequiredforshadingeffects.Section4de-scribeshowslicingandraypickingcanbeprovidedforthedeformedvolumes.Section5discussessomeapplicationsofdynamicdeformations,includinginteractivedeformationandspatialvolumewidgets.Weconcludewithadiscussionofthebene tsandissuesinperformingthedeformationaspartoffragmentshaderprograms.2.RelatedWork

Theimportanceofvolumetricdatasetshasleadtoanen-tire eldofvisualizationtechniquesfortheirdisplay,see[SML98]forasurvey.

Akeyissueinthedisplayofvolumedatasetsistopro-videvisualcuesforcomprehensibility.Directdisplaymeth-odsrelyontransferfunctionsthatdescribehowrayspassingthroughthevolumeareaffectedbythevaluesinthevolume.Thegradientofthescalar eldisoftenusedintransferfunc-tionsasananalogtothesurfacenormalforlightingcom-putations[DCH88].Thisallowsdirectvolumerenderingtoprovideavarietyofsimulatedlightingandstylizeddisplayeffects[ER00].Thevolumedisplaymethodswepresentinthispaperaredesignedtoallowthisrangeofeffects.Displayingvolumesdirectlyatinteractiverateswasorigi-nallyaccomplishedbyspecialpurposehardware,suchasthePixarImageComputerortheVolumeProcard[PHK 99].Currently,mostinteractivedirectvolumerenderingusesstandardgraphicshardwaretocompositeasetoftexturemappedpolygons.ThisideaoriginatedwithCullipandNeu-mann[CN94]andCabraletal.[CCF94],andhasbeenex-tendedovertheyearstomakeuseofnewergraphicshard-warefeatures.See[EHK 04]forasurvey.Ourworkinte-gratesvolumedeformationsintothisubiquitousapproach.Deformationsareoftenusefulinworkingwithvolumedata.Anexampleofrenderingdeformedvolumesthroughprecomputatio …… 此处隐藏：6147字，全部文档内容请下载后查看。喜欢就下载吧 ……