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