参考椭球体是一个数学上定义的地球表面，它近似于大地水准面。 由于其相对简单，参考椭球是大地控制网计算和显示点坐标（如纬度，经度和海拔）的首选的地球表面的几何模型。通常所说地球的形状和大小，实际上就是以参考椭球体的长半轴、短半轴和扁率来表示的。(he reference ellipsoid is a mathematical definition of the earth's surface, which is similar to the geoid. Because of its relative simplicity, the reference ellipsoid is the preferred geometric model of the earth's surface for computing and displaying the point coordinates (such as latitude, longitude and altitude). Usually said the shape and size of the earth, is in fact a reference ellipsoid and the two semi axis and ellipticity expressed.)