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