The Essence of Sensor Fusion —— Weighing each sensor

In the rest of this article, we will focus on physical location, but the same idea applies to any quantity you want to measure. You may think that multiple backup sensors of the same type are feasible, but this often combines their same weaknesses in an unfortunate way.

In contrast, the hybrid system is more powerful. No sensor can make us trust * * *, because each sensor only solves a problem and presents different fragments, and only by combining them can we see the truth.

Let's take a look at some typical sensors used in quadrotor, and discuss their advantages and disadvantages, as well as their role in sensor fusion.

global positioning system (GPS)

GPS has obvious limitations. The sampling error may be two meters, and the deviation will drift with the satellite.

If you want to use the global positioning system to get the accurate position to centimeters, you need to nail it in the proper position and measure it in a few days. This is obviously not what we want. But in fact, moving at high speed in the air, even 100Hz GPS equipment can't smooth the time.

GPS can't tell you the direction you are facing, only the direction you are moving.

In addition, the z resolution (height) can be one tenth of the latitude and longitude. So, we have to leave 20 meters for the ground. This means that GPS alone can't tell you how far you are from the ground, only how far you are from the sea level. The logical solution is to take a reading before takeoff, but then we have a 20-meter error bar. Moreover, in flight, the influence of the ground on GPS signals is different, so we can't assume that these errors will be eliminated in the long run-although they will be eliminated at first!

Obviously, a GPS is not enough.

We can't fly reliably within 20-40 meters above the ground, which is at least five stories high, which is a long distance for the margin. In real life, it's amazing to be able to locate yourself anywhere in the world with a vertical error of 20 meters … but this can't stop us from crashing, without differential GPS ground stations, expensive high-speed receivers and some good topology maps.