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