本 小 节 结 束 * * * Form of Projection                               投影的形成   Types of Projection                               投影法分类   Features of Orthographic Projection     正投影特性   Three-view of Component                      物体的三视图   Exercises                                                练习题 Principles of Orthographic Projection  正 投 影 法 原 理 请点击相应标题显示其内容    Center of projection Plane of projection    Object Lines of projection           Projection        Form of Projection    投影的形成 Projection method :  When the line of projection passes through the                object and the pre - established plane, there will be graphics                 produced on the plane. This method is called projection.   投影法： 投影法是投射线通过物体，向选定的平面投射，           并在该面上得到图形的方法。 请点击鼠标左键显示后面内容       Types of Projection   投影法分类 Projection method 投影法  Central projection method  中心投影法 ( The central projection is mainly used for the pictorial    drawings of buildings.  一般多用于建筑图样 )  Parallel projection method  平行投影法 ( It is used in most engineering drawings.     广泛用于机械、电子、化工等行业的图样)  请点击鼠标左键显示后面内容 3.  Homophyly:      When planar  features or  lines are  inclined  to  the            类似性      projection plane in general, the projection produces                                    similar shapes of the original feature. The length  of                                     projected lines will be shorter than the real length.                  当图形或直线倾斜于投影面时，图形的投影成类似形,线                   段的投影长度比实长短。  2. Accumulation:   When planar features or lines are orthogonal to the      积聚性             projection  plane, the  projection  accumulates to a                                   line or a point.                   当图形或直线垂直于投影面时,其投影积聚成一直线或点。  1.  Authenticity:     When planar  features or  lines  are in  parallel with the          真实性           projection  plane, the projection shows the real  shape                                  or true length of the features being projected.                  当平面图形或直线平行于投影面时,其投影反映实形或实长。           Features of Orthographic Projection 正投影特性 请点击鼠标左键显示后面内容  1. Form of three-view drawings    三视图的形成       Three-View of Component  物体的三视图 请点击鼠标左键显示后面内容 Single orthographic projection 单面正投影        A plan of an object is not always  sufficient to describe it completely.        仅有物体的一个投影不能确定        它的空间形状。 Additional orthographic views can be drawn to sufficiently describe an object. It is necessary to use multiple views in engineering drawings.       为了确定物体的空间形状, 需要增加投影面。故在工程图样中多采用多面视图。   These axes meet at a point    which is called the origin.    三投影轴垂直相交于原点O.  Y-axis→Y轴          Three-View of Component  物体的三视图 请点击鼠标左键显示后面内容 1)  Set up three-view projection system       建立三面投影体系   The three projection planes are  orthogonal from each other. Make up  of  one  projection system.  采用三个相互垂直的投影面,构成投影体系。  V-plane → Vertical plane  正(垂直)平面 H-plane → Horizontal plane  水平面 W-plane→ Wall(Auxiliary vertical) plane 侧(辅助垂直)平面 The intersection lines of the  three projection planes are  called the axes of projection.    三投影面的交线为投影轴  X-axis→X轴  Z-axis→Z轴

第2章正投影法原理.pps