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ViewingIn3D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3DviewingprocessConceptionProjection(投影)ProjectionTheclassofprojectionsTheclassofprojectionsTheclassofprojectionsThesubclassesofPlanarGeometricProjections.正投影图ThreeOrthographicProjectionsThreeOrthographicProjections(三视图)正平行投影(三视图)FrontElevationTopElevationSideElevation正轴侧图(投影面不与坐标轴垂直时的正投影)正轴侧有等轴侧、正二侧和正三侧三种。斜平行投影投影平ThesubclassesofPlanarGeometricProjections.透视投影PerspectiveProjectionThestyleofPerspectiveProjectionOne-pointperspectiveprojection(一点透视)Projection-planecutsonlyoneofthreeaxes.(有一个主灭点,即投影面与一个坐标轴正交,与另外两个坐标轴平行)Two-pointperspectiveprojection(两点透视)Projection-planecutsonlytwoofthreeaxesatthesametime.(有两个主灭点,即投影面与两个坐标轴相交,与另一个坐标轴平行)Three-pointperspectiveprojection(三点透视)Projection-planecutsallofthreeaxesatthesametime.(有三个主灭点,即投影面与三个坐标轴都相交)One-pointperspectiveprojectionTwo-pointandThree-pointPerspectiveProjectionThemathematicsofsimplePerspectiveProjection通常,在由三维物体转换成二维图形的假想相机模型中,物体首先被变换到在观察坐标系中描述,然后再投影到观察平面上成为二维图形.One-pointperspectiveprojectionTransformationofOne-pointperspectiveprojection举例观察变换观察坐标系的定义观察坐标系的定义世界坐标系到观察坐标系观察坐标系的定义