大家知道,两点的相对位置的精确测量,随着尺度的增加,精度渐渐降低。在人造卫星没有问世之前,在陆地上,人们只能通过大地三角网的测量来确定两点间的距离。随着距离的增加,误差也不断积累。洲际的距离、大陆与海岛之间的距离,由于海洋阻隔,其相对位置很难准确测量。即便可以测量,但浩繁的工作量,往往需要很长时间才能得到结果。雷达提供了一个良好的测距工具,但受到视距的限制,超视距雷达,由于工作频率比较低,它的精度是很有限的。在人造卫星出现以后,人们设想将高悬在太空中的卫星作为参考点,地面可以用 We all know that the precise measurement of the relative positions of two points gradually decreases with the increase of the scale. Before the advent of satellites, on land, one could only determine the distance between two points by triangulation of the earth. As the distance increases, errors accumulate. Intercontinental distance, the distance between the mainland and the island, the relative position of the ocean barrier is difficult to accurately measure. Even measurable, but the enormous workload, often takes a long time to get results. Radar provides a good ranging tool, but subject to line-of-sight limitations, OTHR, its accuracy is limited due to the lower frequency of operation. After the advent of satellites, it was assumed that the satellites suspended in space will be used as a reference point and the ground could be used