The geoid is also used as a referencesurface from which to map the topographical features on the planet.
本次制作的地球水准面模型在绘制地球地貌时也将会被用来参考。
2
This height is calculated relative to an average elevation determined for the moon's surface, since there is no such thing as a "sea level" as a reference on the moon.
这个高度是对比月球表面平均高度后计算出来的，因为月球表面并没有“海平面”作为参照。
3
The second part of a spatial reference system is its projection, which defines how to lay out the Earth surface onto a 2-d surface.