The typical trench system in World War I consisted of a series of two, three, four, or more trench lines running parallel to each other and being at least 1 mile (1.6 km) in depth.
第一次世界大战时典型的堑壕体系由2至4条以至更多的一系列壕沟组成，壕沟之间彼此平行，而且纵深可以达到1英里（合1.6公里）。
Three approaches to the graphic representation for lines of intersection are introduced in this article, namely, central projection, parallel skew projection and arc line projection.
本文介绍了图解截交线的三种方法，中心投射法、平行斜投射法、弧线投射法。
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