poing wrote:I didn't read the whole paper, but why do you need 4000 fps?
You don't really need any particular framerate, but the faster it is, the more useful it is. This is a triangulation scheme; so the position of the laser dot as seen by the camera (which is offset by some baseline from the laser source) determines the distance to the reflecting object. Each frame generates just one distance ranging value (unless you've got multiple beam intersections, like through a glass window, or windowscreen, at edges, etc). You put the laser+camera on a spinning platform so you can sweep out 360 degrees. If your camera does 4k fps and your assembly rotates at 10 Hz (600 rpm), you can then acquire 400 points per rotation, which gives you slightly better than 1 degree angular resolution for your range map. Those are the parameters of the "Neato Robotics" XV-11 robotic vacuum cleaner which maps out the borders of the room it is in, in real time.
If your frame rate is much slower, you must take data points much more slowly and it becomes progressively less useful for building a real-time range map. If your robot is supposed to avoid an obstacle which is a person walking by, you want to get at least some data points before the person has been and gone. Likewise if you are also tilting your rotation axis to sweep out an area and build up a 3D range map, your full scan time becomes extremely long if you have to rotate slowly. With more data you can also do averaging to improve your signal to noise ratio.
Instead of tilting or translating the spinning scanner, you can also have it stationary and detect passing objects, like boxes on a conveyor belt, people in a hallway, or cars on a road. With a fast scan you can acquire many depth-map slices and even build up a partial 3D model as the object passes through the scan plane. With a slow scan, you may get only a few points or miss the object completely, if it is moving quickly.
Laser scanners are well known industrial tools. I have read that Google's self-driving car uses a Velodyne HDL-64e
lidar scanner costing $70000. That's a high-end device, but even the cheap ones are in the thousands. There is only one "consumer" lidar I know of, part of the $400 XV-11 vacuum robot. I suspect a Raspberry Pi based device could be cheaper than that.