But since this uses the total flight time of the ball, it gives the total distance the ball has traveled – to the wall and back. If you divide this distance by 2, you get the distance from my hand to the wall, which in this case is 10 meters.
I like this BallDAR method because you can easily imagine throwing a ball and measuring time. But lidar is essentially the same idea: instead of using a ball that moves back and forth, lidar uses light. (this is part of “li” Lidar.)
In theory, you could create a DIY version of a lidar using a flashlight or even a laser pointer. Just aim the laser at something and start the stopwatch once the laser is turned on. Light travels outward, hits the wall, and bounces back. Stop the stopwatch once you see the laser dot on the wall. Then you just need the speed of light to calculate the distance.
Of course, there is also a practical problem: light travel real quickly. its speed is 3 x 108 meters per second. That’s over 670 million miles per hour. If you measure a distance of 10 meters (as in the BallDAR example), the flight time is about 0.000000067 seconds, or 67 nanoseconds.
If you want lidar to work, you need a very fast stopwatch. Galileo actually tried a similar method in his experiments to determine the speed of light. Granted, he didn’t have a laser or even a fancy stopwatch, but that didn’t stop him from trying. (He couldn’t actually take measurements.)
Most versions of lidar use a single laser with a detector. When a short pulse is sent, the computer measures the time it takes to return the signal to the device. Then a simple calculation to get the distance traveled by the light.
But this only measures a distance. It’s not enough to make an awesome 3D lidar surface image showing the shape of an object.In order to get it, you need more data.
If you know where the laser is pointing, you can get the distance and bearing to you one point on the surface of an object. Next, you simply point the laser in a slightly different direction and repeat this, usually with a rotating mirror.keep doing this and you can get a a lot the point. After you have collected thousands of them, the points will merge to form an image that is shaped like the surface of the object you are scanning.
But using a laser with a rotating mirror is not only expensive, but it is also too bulky to fit into a phone. So how does lidar work on the iPhone? I just want to say “this is amazing” – because that’s what it seems to me. What I do know is that instead of using a beam of light to measure distance, the iPhone uses a grid of dots of near-infrared wavelengths emitted by the phone (like the light emitted by an IR TV remote). These multiple beams are generated by vertical cavity surface emitting lasers or VCSEL arrays. It’s basically many lasers on a single chip, which makes it possible to put lidar in a smartphone.
