A rangefinder is a device that measures distance from the observer to a target, in a process called ranging.
Other devices measure distance using trigonometry are stadiametric, coincidence and stereoscopic rangefinders. Older methodologies that use a set of known information (usually distance or target sizes) to make the measurement, have been in regular use since the 18th century.
Special ranging makes use of actively synchronized transmission and travel time measurements. The time difference between several received signals is used to determine exact distances. This principle is used in satellite navigation. In conjunction with a standardized model of the Earth's surface, a location on that surface may be determined with high accuracy. Ranging methods without accurate time synchronization of the receiver are called pseudorange, used, for example, in GPS positioning.
With other systems ranging is obtained from passive radiation measurements only: the noise or radiation signature of the object generates the signal that is used to determine range. This asynchronous method requires multiple measurements to obtain a range by taking multiple bearings instead of appropriate scaling of active pings, otherwise the system is just capable of providing a simple bearing from any single measurement.
Ranging is the term applied to distance measurement with moving objects. Combining several measurements in a time sequence leads to tracking and tracing. A commonly used term for residing terrestrial objects is surveying.
Laser rangefinders are used for many things today, including golf. People can use this technology not only to measure the yardage of a particular shot but to gauge slope and wind as well. The technology makes it very simple to obtain yardage. In a typical rangefinder, one aims the reticle at the flagstick and presses a button to get the yardage. There has been debate over whether they should be allowed in tournaments. While their use is banned on the professional level, they are becoming widely used on the amateur level.
Rangefinders may be used by users of firearms over long distances, to measure the distance to a target to allow for projectile drop. Until the development of electronic means of measuring range during the Second World War, warships used very large optical rangefinders—with a baseline of many meters—to measure range for naval gunnery.
Rangefinders are used for surveying in forestry. Special devices with anti-leaf filters are used.
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