概述Overview

    两立体相交，也称两立体相贯，它们表面的交线称为相贯线。工程形体一般是多种几何形体的组合，当这些基本几何体表面相交时，会产生相贯线。相贯线是几何体表面的分界线。在绘制工程形体的视图时，需要画出相贯线的投影。坝体与闸墩之间、进水口处、两廊道相交处均有相贯线。

       Two solid intersection, also known as two solid intersecting, their surface intersection line known as intersecting line.Engineering bodies are usually a combination of geometric bodies. When these basic surfaces intersect, intersecting lines are generated.Intersecting lines are the boundaries on the surface of geometry.When drawing the view of the engineering body, it is necessary to draw the projection of the intersecting line.There are intersecting lines between dam body and gate pier, water inlet and intersection of two corridors.

                 

      由于立体的形状、大小及相互位置的不同，相贯线的形状也各不相同，可能是直线段或平面曲线段的组合，也可能是空间曲线。但是，所有相贯线都有下列基本性质：    

      1. 相贯线是相交两立体表面的共有线，它的投影必在两立体投影重叠部分的范围以内；

      2. 由于立体有一定的范围，所以相贯线一般是封闭的；

      3. 相贯线是相交立体表面间的分界线，每个参加相交的立体的轮廓线都不能穿过相贯线而进入另一立体内部。

      当一立体全部棱线或素线与另一立体表面相交时称为全贯，全贯时一般有两条相贯线； 当两立体都只有部分棱线或素线与另一立体表面相交时称为互贯，互贯时则只有一条相贯线。

      Due to the different shape, size and position of the solid, the shape of the intersecting line is also different, which may be a combination of a straight line or a plane curve, or a space curve.However, all intersecting lines have the following basic properties:

      1. The intersecting line is the common line of intersecting two stereoscopic surfaces, and its projection must be within the scope of the overlapping part of the two stereoscopic projections;

      2. The intersecting line is generally closed due to a certain stereoscopic range;

      3. Intersecting line is the dividing line between intersecting solid surfaces. The contour line of each intersecting solid cannot cross the intersecting line and enter the interior of another solid.

             求相贯线可分析两立体的相对位置及其相对于投影面的位置；分析相贯线的性质——空间形状及投影情况，选择解题方法。具体步骤如下：

              1. 求相贯线上的控制点及中间点。控制点包括：轮廓线（棱线）上的点，极限位置点——最高最低点、最左最右点、最前最后点，相贯线端点，曲线特征点（如椭圆的长短轴端点、曲线的拐点等）；

     2. 根据相贯线的性质依次连接所求各点；

     3. 区别相贯线各段的可见性，并补全立体的投影。

     The relative position of two solids and their position relative to the projection plane can be analyzed by calculating the intersecting line.Analyze the properties of intersecting line - space shape and projection, and choose the method to solve the problem.The specific steps are as follows:

      1. Find the control points and intermediate points of the intersecting line.Control points include: the point on the contour (prism), the limit position point -- the highest and lowest point, the left and right point, the first and last point, the endpoint of the intersecting line, the curve feature point (such as the short and long axis endpoint of the ellipse, the inflection point of the curve, etc.);

      2. Connect the desired points successively according to the property of the intersecting line;

      3. Distinguish the visibility of each segment of the intersecting line, and complete the three-dimensional projection.