How does inertial guidance work?
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There’s a few different ways to do this.
The systems I use at work are called IMU’s (Inertial Motion Units). They typically use fibre optic gyroscopes to monitor movement around a 3D environment.
Over the last few decades, we’ve gone from buying gyroscopes out of decommissioned cruise missiles (the paperwork was something else), to tiny little units that are built directly into the end unit.
The units detect acceleration along XYZ axis and rotation around those axis.
The accuracy is roughly determined by the cost, though there’s a huge number of variables that can affect that.
An example of the accuracy: we used a back pack lidar scanner, mounted on a car, to scan a few kilometres of tunnel. We had precise (mm accurate datums) at each end and the scanners IMU had only lost a few hundred mm. That’s not a particularly accurate IMU, it’s kinda more meant for small UAV guidance in enclosed spaces.
If you’re having trouble understanding how the gyroscope can measure motion, think about how a bicycle wheel resists changing its plane of rotation. Or a spinning top remains standing. The gyroscope measures the force needed to change its position. The gyroscopes spin at known speeds and are calibrated at the factory to output correct values.
Fibre optic gyroscopes are basically the same, but rather than physical force, they measure the change in travel time of a light signal around a fibre loop as the gyroscope moves.
I’m sure there are other types of IMUs out there, but these are the ones I’ve got end user experience with
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