Surveying overview

Surveying is the technique and science ofthrough the use of a vertical measuring rod.
accurately determining the terrestrial orAs late as the 1990's the basic tools used in
three-dimensional space position of points and theplanar surveying were a tape measure for
distances and angles between them. These pointsdetermining shorter distances, a level for
are usually, but not exclusively, associated withdetermine height or elevation differences, and a
positions on the surface of the Earth, and aretheodolite, set on a tripod, with which one can
often used to establish land maps and boundariesmeasure angles (horizontal and vertical), combined
for ownership or governmental purposes. In orderwith triangulation. Starting from a benchmark, a
to accomplish their objective, surveyors useposition with known location and elevation, the
elements of geometry (Greek: measuring thedistance 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 thedistance measurement device (EDM) and can also
development of the human environment since thebe 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 andmade 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 ofwith 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 ofreflector or prism (used to return the ambient
legal boundarieslight used for distancing) to return distance
Historically, angles and distances were measuredmeasurements, are fully robotic, and can even
using a variety of means, such as chains with linkse-mail point data to the office computer and
of a known length, for instance a Gunter's Chainconnect to satellite positioning systems, such as a
(see Edmund Gunter), or measuring tapes madeGlobal Positioning System (GPS). Though GPS
of steel or invar. In order to measure horizontalsystems have increased the speed of surveying,
distances, these chains or tapes would be pulledthey are still only accurate to about 20
taut according to temperature, to reduce saggingmm.[citation needed] As well GPS systems do not
and slack. Additionally, attempts to hold thework in areas with dense tree cover. It is
measuring instrument level would be made. Inbecause of this that total stations have not
instances of measuring up a slope, the surveyorcompletely phased out earlier instruments.
might have to "break" (break chain) theRobotics allows surveyors to gather precise
measurement- that is, raise the rear part of themeasurements without extra workers to look
tape upward, plumb from where the lastthrough and turn the telescope or record data. A
measurement ended.faster way to measure (no obstacles) is with a
Historically, horizontal angles were measured usinghelicopter with laser echolocation, combined with
a compass, which would provide a magneticGPS to determine the height of the helicopter. To
bearing, from which deflections could beincrease precision, beacons are placed on the
measured. This type of instrument was laterground (about 20 km apart). This method reaches
improved upon, through more carefully scribeda precision of about 5 mm.
discs providing better angular resolution, as well asWith the triangulation method, one first needs to
through mounting telescopes with reticles forknow the horizontal distance to the object. If this
more precise sighting atop the disc (seeis not known or cannot be measured directly, it is
theodolite). Additionally, levels and calibrated circlesdetermined as explained in the triangulation article.
allowing measurement of vertical angles wereThen the height of an object can be determined
added, along with verniers for measurementby measuring the angle between the horizontal
down to a fraction of a degree- such as aplane 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 withdetermine the height of a mountain, one should do
an altimeter — basically a barometerthis from sea level (the plane of reference), but
— using air pressure as an indication ofhere 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 assteps, first determining the position of one point,
precise levels, have been developed. Levels arethen moving to that point and doing a relative
calibrated to provide a precise plane from whichmeasurement, and so on until the mountaintop is
differentials in height between the instrument andreached.
the point in question can be measured, typically