The compass is mainly used to indicate the orientation, does not explicitly require the horizontal attitude, and has no requirements for speed measurement and positioning. It is often used for low-speed and small-sized vehicles such as large-tonnage ships. In order to ensure the azimuth accuracy, external speed and latitude compensation are generally required during driving. Due to the large tonnage, the compensation can be manually bound (no need to be frequent). To save costs, you can use a bubble (scientific name electrolyte tilt sensor) to level, instead of using three or two accelerometers. The use of bubble leveling in the Strapdown scriptures seems to be rare in domestic research and use. Compass is generally not used for aircraft with high speed and high maneuvering. It is not suitable for vehicles with turning and acceleration and deceleration.
The attitude and attitude instrument requires horizontal attitude and azimuth at the same time. There is no strict requirement for speed measurement and positioning. It is usually used for aircraft. When the maneuver is slightly larger, it needs a combination of external reference position or speed such as GPS. Otherwise, the maneuver time is long and the error is easy to exceed the limit. The attitude and attitude instrument generally uses the medium and low-precision IMU, and it is impossible to find the north by static. It is often used to find the north by combining navigation and maneuvering, or to find the north by means of the magnetic compass. If there is no external reference combination, it is only suitable for smooth cruise or short-time maneuvering. A person who only provides a horizontal posture (no orientation or accuracy is required) can be called a horizon or a vertical gyroscope.
The navigation information provided by the inertial navigation system is comprehensive, including horizontal attitude and orientation, speed and positioning, and even angular rate and acceleration. It is often of high precision and can be used for pure inertial navigation for a long time (at least 10-20 min or more). The gyro compass has self-seeking ability during the operation, that is, it constantly seeks the north to make the azimuth not divergence; and the inertial navigation does not require this function, only the change of the attitude is integrated, and the azimuth error will gradually increase. The inertial navigation system can be used near the poles of the earth. The attitude and attitude can be used at the pole if the orientation is not checked, but the compass can't (it can be made at high latitudes). Of course, if it is a combination of low-precision MEMS-IMU and GPS, MEMS can help improve the speed and positioning performance of GPS. It can also be called MEMS as an inertial navigation system; otherwise, if the main purpose is to use the combined horizontal attitude and orientation information, It is better to call it the attitude monitor (or inertial measurement unit, but not navigation). Finally, based on the hardware of the inertial navigation system, it is easy to realize the functions of the compass and the attitude instrument by adapting the software. Therefore, the inertial navigation system hardware should be the most advanced.
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