为了在一个类图上建模继承，从子类(要继承行为的类)拉出一条闭合的，单键头(或三角形)的实线指向超类。
To model inheritance on a class diagram, a solid line is drawn from the child class (the class inheriting the behavior) with a closed, unfilled arrowhead (or triangle) pointing to the super class.
在GPS测量中，往往需要计算三角形、多边形闭合差，以便及时发现观测粗差、衡量GPS观测精度。
In GPS surveying, we usually need to compute closure difference of triangle or polygon, so as to search surveying gross errors and estimate GPS observing precision.
在GPS测量中，往往需要计算三角形、多边形闭合差，以便及时发现观测粗差、衡量GPS观测精度。
In GPS surveying, we usually need to compute closure difference of triangle or polygon, so as to search surveying gross errors and estimate GPS observing precision.
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