Coordinate Systems

ENU

• a local projection from sphere to cylinder (base point is not fixed)

• z axis is always the opposite direction of gravity (z can represent altitude)

• the far from base point, the greater distortion of the space

GENU

• a global projection from sphere to cylinder (base point is fixed)

• the far from base point, the greater difference between z axis and gravity (z cannot represent altitude anymore)

• no distortion of the space, no matter how far from the base point

ECEF

• the earth-centered coordinate system

• no distortion, but not intuitive for objects moving on earth surface

References

• https://zhuanlan.zhihu.com/p/33295151

• https://en.wikipedia.org/wiki/Mercator_projection

• https://en.wikipedia.org/wiki/Local_tangent_plane_coordinates

• https://en.wikipedia.org/wiki/Geographic_coordinate_conversion#From_ECEF_to_ENU