6. Fly over an area where light changes dramatically and rapidly.
7. Fly over surfaces extremely dark (lux<10) or extremely bright (lux>10,000).
8. Fly over material surfaces that is good at absorbing ultrasonic waves (like thick
carpet).
9. Fly over surfaces without clear textures.
10. Fly over surfaces with highly repeating textures (small grid brick in the same
color).
11. Fly over surfaces that are tilting over 30 degrees (could not receive the echo of
the ultrasonic wave).
12. Flying speed should be controlled not to be too fast. When the drone is 1
meter against the ground, the flying speed should not be over 5m/ 2 meter
against the ground, the flying speed should not be over 14m/s.
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