由于在工程图学中，用正投影法解决画法几何中的某些度量和定位问题往往很不方便。
In engineering drawing, it is always inconvenient for orthographic projection to solve some measurement and orientation problems.
在画法几何投影变换中，不论用换面法或旋转法，一般位置直线均需两次变换才能变成投影面垂直线。
In the transformation of descriptive geometry, no matter the method of change plane or revolve, the oblique line can be changed to a vertical line in two successive transformations.
变方向折线剖面是在地形、地质情况较为复杂地区普遍采用的实测地质剖面方法。其地质剖面图目前一般用几何作图方法以投影法成图。
The construction of the direction changing section is a method of measuring a geological section applied commonly in areas with complex topographic and geological condition.
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