The ranging principle can be basically reduced to measuring the time required for light to and from the target, and then calculate the distance d through the light speed c = 299792458m / s and the atmospheric refractive index n. Because it is difficult to measure the time directly, it is usually to measure the phase of continuous wave, which is called phase measuring rangefinder. Of course, there are also pulse rangefinders, typically the di-3000 of wild
It should be noted that phase measurement is not to measure the phase of infrared or laser, but to measure the signal phase modulated on infrared or laser. There is a hand-held laser rangefinder in the construction industry, which is used for house measurement, and its working principle is the same.