| Surveying is the technique and science of | | | | through the use of a vertical measuring rod. |
| accurately determining the terrestrial or | | | | As late as the 1990's the basic tools used in |
| three-dimensional space position of points and the | | | | planar surveying were a tape measure for |
| distances and angles between them. These points | | | | determining shorter distances, a level for |
| are usually, but not exclusively, associated with | | | | determine height or elevation differences, and a |
| positions on the surface of the Earth, and are | | | | theodolite, set on a tripod, with which one can |
| often used to establish land maps and boundaries | | | | measure angles (horizontal and vertical), combined |
| for ownership or governmental purposes. In order | | | | with triangulation. Starting from a benchmark, a |
| to accomplish their objective, surveyors use | | | | position with known location and elevation, the |
| elements of geometry (Greek: measuring the | | | | distance and angles to the unknown point are |
| Earth), engineering, trigonometry, mathematics, | | | | measured. A more modern instrument is a total |
| physics, and law. | | | | station, which is a theodolite with an electronic |
| Surveying has been an essential element in the | | | | distance measurement device (EDM) and can also |
| development of the human environment since the | | | | be used for leveling when set to the horizontal |
| beginning of recorded history (ca. 5000 years ago) | | | | plane. Since their introduction, total stations have |
| and it is a requirement in the planning and | | | | made the technological shift from being |
| execution of nearly every form of construction. | | | | optical-mechanical devices to being fully electronic |
| Its most familiar modern uses are in the fields of | | | | with an onboard computer and software. Modern |
| transport, building and construction, | | | | top-of-the-line total stations no longer require a |
| communications, mapping, and the definition of | | | | reflector or prism (used to return the ambient |
| legal boundaries | | | | light used for distancing) to return distance |
| Historically, angles and distances were measured | | | | measurements, are fully robotic, and can even |
| using a variety of means, such as chains with links | | | | e-mail point data to the office computer and |
| of a known length, for instance a Gunter's Chain | | | | connect to satellite positioning systems, such as a |
| (see Edmund Gunter), or measuring tapes made | | | | Global Positioning System (GPS). Though GPS |
| of steel or invar. In order to measure horizontal | | | | systems have increased the speed of surveying, |
| distances, these chains or tapes would be pulled | | | | they are still only accurate to about 20 |
| taut according to temperature, to reduce sagging | | | | mm.[citation needed] As well GPS systems do not |
| and slack. Additionally, attempts to hold the | | | | work in areas with dense tree cover. It is |
| measuring instrument level would be made. In | | | | because of this that total stations have not |
| instances of measuring up a slope, the surveyor | | | | completely phased out earlier instruments. |
| might have to "break" (break chain) the | | | | Robotics allows surveyors to gather precise |
| measurement- that is, raise the rear part of the | | | | measurements without extra workers to look |
| tape upward, plumb from where the last | | | | through and turn the telescope or record data. A |
| measurement ended. | | | | faster way to measure (no obstacles) is with a |
| Historically, horizontal angles were measured using | | | | helicopter with laser echolocation, combined with |
| a compass, which would provide a magnetic | | | | GPS to determine the height of the helicopter. To |
| bearing, from which deflections could be | | | | increase precision, beacons are placed on the |
| measured. This type of instrument was later | | | | ground (about 20 km apart). This method reaches |
| improved upon, through more carefully scribed | | | | a precision of about 5 mm. |
| discs providing better angular resolution, as well as | | | | With the triangulation method, one first needs to |
| through mounting telescopes with reticles for | | | | know the horizontal distance to the object. If this |
| more precise sighting atop the disc (see | | | | is not known or cannot be measured directly, it is |
| theodolite). Additionally, levels and calibrated circles | | | | determined as explained in the triangulation article. |
| allowing measurement of vertical angles were | | | | Then the height of an object can be determined |
| added, along with verniers for measurement | | | | by measuring the angle between the horizontal |
| down to a fraction of a degree- such as a | | | | plane and the line through that point at a known |
| turn-of-the-century Transit (surveying). | | | | distance and the top of the object. In order to |
| The simplest method for measuring height is with | | | | determine the height of a mountain, one should do |
| an altimeter — basically a barometer | | | | this from sea level (the plane of reference), but |
| — using air pressure as an indication of | | | | here the distances can be too great and the |
| height. But for surveying more precision is needed. | | | | mountain may not be visible. So it is done in |
| Toward this end, a variety of means, such as | | | | steps, first determining the position of one point, |
| precise levels, have been developed. Levels are | | | | then moving to that point and doing a relative |
| calibrated to provide a precise plane from which | | | | measurement, and so on until the mountaintop is |
| differentials in height between the instrument and | | | | reached. |
| the point in question can be measured, typically | | | | |