体绘制技术简介

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1、DirectVolumeRenderingofDirectVolumeRenderingof3DDataSets3DDataSets三维空间规则数据场直接体绘制三维空间规则数据场直接体绘制2005-12-61ContentsSummaryContentsSummary1.WhatisVolumeRendering?2.ResamplinginVolumeRendering3.VolumeRenderingPipeline4.OpticalModel5.ImageOrderVolumeRendering6.ObjectOrde

2、rVolumeRendering7.FrequencyDominVolumeRendering2005-12-621.WhatisVolumeRendering?1.WhatisVolumeRendering?¾Methodofdisplayingvolumetricdataasatwo-dimensionalimage¾Theprocessofgeneratinga2Dimagefrom3DvolumeiscalledvolumerenderingvolumerenderingV(alsocalledDirectVolum

3、eRendering,DVR)2005-12-63DirectVolumeRenderingDirectVolumeRenderingDirectlyNointermediateBasicidea:¾不构造中间几何图素，直接将物体空间中的数据采样点的光亮度值变换到图象平面;¾即计算各数据采样点的光亮度值对屏幕上象素点的贡献，累积合成得到最后的图象。CommoncoreofallAlgorithms:Resampling(重新采样)+Compositing(图象合成)2005-12-64VolumeDataRepresenta

4、tion(VolumeDataRepresentation(体数据表示体数据表示))•AVolumeissometimescalleda3Dimage–Itisa3Darrayofpointsamples,calledvoxels(volumeelements，体元)–apointwithoutasizeinthree-dimensionalspacePixelsVoxels2005-12-65•3Dvolumedataarerepresentedbyafinitenumberofcrosssectionalslices(h

5、encea3Draster)•Oneachvolumeelement(voxel),storesadatavalue(ifitusesonlyasinglebit,thenitisabinarydataset.Normally,weseeagrayvalueof8to16bitsoneachvoxel.)Nx2Darraies=3Darray2005-12-66WhatisaWhatisaVoxelVoxel??––TwodefinitionsTwodefinitionsAvoxelisacubiccell,whichhas

6、asinglevaluecovertheentirecubicregionAvoxelisadatapointatacornerofthecubiccellThevalueofapointinsidethecellisdeterminedbyinterpolation2005-12-672.2.ResamplingResamplinginVolumeRenderinginVolumeRendering（（重采样）重采样）体绘制中地重采样是基于信号处理中的采样理论的••SomebasicconceptsSomebasiccon

7、cepts¾¾Signal(ContinuoussignalSignal(Continuoussignal、、DiscreteDiscretesignal)signal)¾¾SamplingsamplesSamplingsamples••ForierForierSpectrumSpectrum、、ForierForierTransformTransform••FilteringFiltering••Reconstruction&Reconstruction&ResamplingResampling2005-12-68Resa

8、mplingResampling(interpolation)(interpolation)•Generatingnewaddresses&newvalueintothevoxelspaceeyepointResamplingpointSamplingpointViewingrayImag