1. ECEF rectangular coordinate system（ECEF直角坐标系）
The usual rectangular coordinate system [x, y, z], here in referred to as the ECEF coordinate system, has its origin at the Earth’s center of mass with its x-axis extend through the intersection of the prime meridian (0deg longitude) and the equator (0deglatitude). The z-axis extends through the true north pole (i.e., coincident with the Earth spin axis). The y-axis completes the right-handed coordinate system, passing through the equator and 90deg longitude, as shown in Figure 1.1.
如图1.1所示，通常的直角坐标系[x，y，z]，这里称为ECEF坐标系，其起源位于地球的质心，其x轴延伸通过本初子午线（0度经度）和赤道（0deglatitude）的交点。 z轴延伸通过真正的北极（即，与地球旋转轴重合）。 y轴完成右手坐标系，穿过赤道和90度经度。
2.LLH(lattitude Longtitude Height)
3.ECEF to LLH
convert ECEF to LLH
https://docs.eegeo.com/unity/latest/docs/examples/ecef-coordinate-system/