计算机图形学3D图形表示方式.ppt
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1、Viewing In 3DChapter 5n如何在二维平面上显示三维物体n表示问题n遮挡关系的反映n真实感问题投影三维形体的表示消隐光照与着色The basic questions of 3D graphics3D viewing processClip againstviewvolumeProject ontoprojectionplaneTransform into viewport in 2D device coordinates for display3D world-coordinate output primitivesClipped world coordinates2D de
2、vice coordinates primitivesFig.Conceptual model of the 3D viewing process.Conception Projections transform points in a coordinate system of dimension n into points in a coordinate system of dimension less than n.Projection Definition:The projection of a 3D object is defined by straight projection ra
3、ys(called projectors)emanating from a center of projection,passing through each point of the object,and intersecting a projection plane to form the projection.ProjectionsProjections Parameter:n projection centern projection plane The class of projectionsn Perspective Projection The distance between
4、the center of projection and the projection plane is finite.nParallel Projection The distance between the center of projection and the projection plane is infinite.The class of projectionsABABCenter of projectionprojectorsProjection plane(a)Fig.(a)perspective projection (b)parallel projection.ABABCe
5、nter of projectionprojectorsProjection plane(b)The subclasses of Planar Geometric Projections.Planar geometric projectionsParallel Perspective Orthographic Oblique Top(plan)Front elevationSide elevationAxonometricIsometricOther Other Cabinet Cavalier One-pointThree-pointTwo-point.Three Orthographic
6、ProjectionsProjectors for top viewProjection plan (front view)Projectors for side viewProjectors for front viewProjection plan (top view)Projection plan (side view)Three Orthographic Projections(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)Front ElevationVUXYYZ主视图侧视图俯视图txtztxtytyt
7、zTop ElevationVUXYYZ主视图侧视图俯视图txtztxtytytzSide ElevationVUXYYZ主视图侧视图俯视图txtztxtytytzPerspective Projectionn Vanishing Point.The perspective projections of any set of parallel lines that are not parallel to the projection plane converge to a vanishing point.nAxis Vanishing Point If the set of lines is
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- 计算机 图形学 图形 表示 方式
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