What is land survey


Surveying overview

Surveying is the technique and sciencerod.
of accurately determining theAs late as the 1990's the basic tools
terrestrial or three-dimensional spaceused in planar surveying were a tape
position of points and the distances andmeasure for determining shorter
angles between them. These points aredistances, a level for determine height
usually, but not exclusively, associatedor elevation differences, and a
with positions on the surface of thetheodolite, set on a tripod, with which
Earth, and are often used to establishone can measure angles (horizontal and
land maps and boundaries for ownershipvertical), combined with triangulation.
or governmental purposes. In order toStarting from a benchmark, a position
accomplish their objective, surveyorswith 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, andis a total station, which is a
law.theodolite with an electronic distance
Surveying has been an essential elementmeasurement device (EDM) and can also be
in the development of the humanused for leveling when set to the
environment since the beginning ofhorizontal plane. Since their
recorded history (ca. 5000 years ago)introduction, total stations have made
and it is a requirement in the planningthe technological shift from being
and execution of nearly every form ofoptical-mechanical devices to being
construction. Its most familiar modernfully 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 therequire a reflector or prism (used to
definition of legal boundariesreturn the ambient light used for
Historically, angles and distances weredistancing) to return distance
measured using a variety of means, suchmeasurements, 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 (seecomputer and connect to satellite
Edmund Gunter), or measuring tapes madepositioning systems, such as a Global
of steel or invar. In order to measurePositioning System (GPS). Though GPS
horizontal distances, these chains orsystems have increased the speed of
tapes would be pulled taut according tosurveying, they are still only accurate
temperature, to reduce sagging andto about 20 mm.[citation needed] As well
slack. Additionally, attempts to holdGPS systems do not work in areas with
the measuring instrument level would bedense tree cover. It is because of this
made. In instances of measuring up athat total stations have not completely
slope, the surveyor might have tophased out earlier instruments. Robotics
"break" (break chain) the measurement-allows surveyors to gather precise
that is, raise the rear part of the tapemeasurements without extra workers to
upward, plumb from where the lastlook through and turn the telescope or
measurement ended.record data. A faster way to measure (no
Historically, horizontal angles wereobstacles) is with a helicopter with
measured using a compass, which wouldlaser echolocation, combined with GPS to
provide a magnetic bearing, from whichdetermine the height of the helicopter.
deflections could be measured. This typeTo increase precision, beacons are
of instrument was later improved upon,placed on the ground (about 20 km
through more carefully scribed discsapart). This method reaches a precision
providing better angular resolution, asof about 5 mm.
well as through mounting telescopes withWith the triangulation method, one first
reticles for more precise sighting atopneeds to know the horizontal distance to
the disc (see theodolite). Additionally,the object. If this is not known or
levels and calibrated circles allowingcannot be measured directly, it is
measurement of vertical angles weredetermined as explained in the
added, along with verniers fortriangulation article. Then the height
measurement down to a fraction of aof an object can be determined by
degree- such as a turn-of-the-centurymeasuring the angle between the
Transit (surveying).horizontal plane and the line through
The simplest method for measuring heightthat point at a known distance and the
is with an altimeter — basically atop of the object. In order to determine
barometer — using air pressure as anthe height of a mountain, one should do
indication of height. But for surveyingthis from sea level (the plane of
more precision is needed. Toward thisreference), but here the distances can
end, a variety of means, such as precisebe too great and the mountain may not be
levels, have been developed. Levels arevisible. So it is done in steps, first
calibrated to provide a precise planedetermining the position of one point,
from which differentials in heightthen moving to that point and doing a
between the instrument and the point inrelative measurement, and so on until
question can be measured, typicallythe mountaintop is reached.
through the use of a vertical measuring



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