1. Earth-Centered Inertial Frame ECI (Earth-Centered Inertial Frame)
inertial coordinate system refers to a coordinate system that has no acceleration and rotation relative to other parts of the universe. It is a mathematical relationship that describes position, velocity, acceleration, attitude and angular velocity. The inertial sensor measures the movement relative to the inertial coordinate system. After calculating the attitude, position, and speed in the inertial system, it is projected to the local navigation coordinate system.
The geocentric inertial coordinate system does not rotate with the rotation of the earth.
2. Earth-Centered Earth-Fixed Frame ECEF (Earth-Centered Earth-Fixed Frame)
The similarities and differences between ECEF and ECI:
(1). The origin is the same (both are the center of mass of the earth)
(2). The Z axis is the same
(3). The x and y axes of ECI are fixed and do not rotate with the rotation of the earth. The x and y axes of ECEF are opposite
3. Local Navigation Frame:
The local navigation frame moves relative to the earth. The origin of the navigation coordinate system and its coordinate axis change with the movement of the carrier.
North-East-Earth (NED) vs. East-North-Heaven (ENU)
is often NED
The navigation coordinate system provides the attitude relative to the north, east and vertical directions. For example, the heading angle (yaw) of 45 degrees refers to the angle relative to the north direction. The navigation coordinate system represents the attitude of the carrier, and the speed is more convenient
4. Carrier coordinate system (b system/Body Frame/Vehicle Frame)
Correspondence between carrier coordinate system and navigation coordinate system
5. Conversion methods between coordinate systems
5.1 Cosine matrix method
5.2 Euler angle method