计算机图形学3D图形表示方式.pptx

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Thebasicquestionsof3Dgraphics

3DviewingprocessClipagainstviewvolumeProjectontoprojectionplaneTransformintoviewportin2Ddevicecoordinatesfordisplay3Dworld-coordinateoutputprimitivesClippedworldcoordinates2DdevicecoordinatesprimitivesFig.Conceptualmodelofthe3Dviewingprocess.

ConceptionProjectionstransformpointsinacoordinatesystemofdimensionnintopointsinacoordinatesystemofdimensionlessthann.12

ProjectionDefinition:Theprojectionofa3Dobjectisdefinedbystraightprojectionrays(calledprojectors)emanatingfromacenterofprojection,passingthrougheachpointoftheobject,andintersectingaprojectionplanetoformtheprojection.0102

2projectionplane1projectioncenterProjection’sParameter:Projections

TheclassofprojectionsPerspectiveProjectionThedistancebetweenthecenterofprojectionandtheprojectionplaneisfinite.ParallelProjectionThedistancebetweenthecenterofprojectionandtheprojectionplaneisinfinite.

TheclassofprojectionsA’B’AB?CenterofprojectionprojectorsProjectionplane(a)Fig.(a)perspectiveprojection(b)parallelprojection.A’B’ABCenterofprojectionprojectorsProjectionplane(b)

Thesubclassesof

PlanarGeometricProjections.PlanargeometricprojectionsParallelPerspectiveOrthographicObliqueTop(plan)FrontelevationSideelevationAxonometricIsometricOtherOtherCabinetCavalierOne-pointThree-pointTwo-point

ThreeOrthographicProjectionsProjectorsfortopviewProjectionplan(frontview)ProjectorsforsideviewProjectorsforfrontviewProjectionplan(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txtztxtytytz

TopElevationVUXYYZ主视图侧视图俯视图txtztxtytytz

SideElevationVUXYYZ主视图侧视图俯视图txtztxtytytz

PerspectiveProjectionTheperspectiveprojectionsofanyseto