计算机图形学3D图形表示方式.ppt

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1、ViewingIn3DChapter5如何在二维平面上显示三维物体表示问题遮挡关系的反映真实感问题投影三维形体的表示消隐光照与着色Thebasicquestionsof3Dgraphics3DviewingprocessClipagainstviewvolumeProjectontoprojectionplaneTransformintoviewportin2Ddevicecoordinatesfordisplay3Dworld-coordinateoutputprimitivesClippedworldcoordinates2Ddevicecoordinates

2、primitivesFig.Conceptualmodelofthe3Dviewingprocess.ConceptionProjectionstransformpointsinacoordinatesystemofdimensionnintopointsinacoordinatesystemofdimensionlessthann.ProjectionDefinition:Theprojectionofa3Dobjectisdefinedbystraightprojectionrays(calledprojectors)emanatingfromacentero

3、fprojection,passingthrougheachpointoftheobject,andintersectingaprojectionplanetoformtheprojection.ProjectionsProjection’sParameter:projectioncenterprojectionplaneTheclassofprojectionsPerspectiveProjectionThedistancebetweenthecenterofprojectionandtheprojectionplaneisfinite.ParallelProj

4、ectionThedistancebetweenthecenterofprojectionandtheprojectionplaneisinfinite.TheclassofprojectionsA’B’ABCenterofprojectionprojectorsProjectionplane(a)Fig.(a)perspectiveprojection(b)parallelprojection.A’B’ABCenterofprojectionprojectorsProjectionplane(b)ThesubclassesofPlanarGeometricP

5、rojections.PlanargeometricprojectionsParallelPerspectiveOrthographicObliqueTop(plan)FrontelevationSideelevationAxonometricIsometricOtherOtherCabinetCavalierOne-pointThree-pointTwo-point.ThreeOrthographicProjectionsProjectorsfortopviewProjectionplan(frontview)ProjectorsforsideviewProje

6、ctorsforfrontviewProjectionplan(topview)Projectionplan(sideview)ThreeOrthographicProjections(三视图）VUXYYZ主视图侧视图俯视图YZX正平行投影（三视图）VUXYYZ主视图侧视图俯视图txtztxtytytz(a,b)FrontElevationVUXYYZ主视图侧视图俯视图txtztxtytytzTopElevationVUXYYZ主视图侧视图俯视图txtztxtytytzSideElevationVUXYYZ主视图侧视图俯视图txtztxtytytzPerspect

7、iveProjectionVanishingPoint.Theperspectiveprojectionsofanysetofparallellinesthatarenotparalleltotheprojectionplaneconvergetoavanishingpoint.AxisVanishingPointIfthesetoflinesisparalleltooneoftheprincipalaxes,thevanishingpointiscalledanaxisvanishingpoint.ThestyleofPerspectiveProjectionP

8、erspe