Techniques of Land Surveying The structure of Presentation: Introduction to Land Survey History of Land Survey Types of Land Survey Measurements Modern Technologies Geographical Information System Photogrammetry LiDAR Airborne LiDAR 3D laser scanners

1. Techniques of Land Surveying
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2. Definition
Surveying or land surveying is the technique, profession, and science of accurately
determining the terrestrial or three-dimensional position of points and the distances
and angles between them.
Geographic positions are specified relative to a fixed reference. Positions on the
globe, for instance, may be specified in terms of angles relative to the centre of the
Earth, the equator, and the prime meridian.
Surveys are often used to establish land maps and boundaries for ownership, locations
(building corners, surface location of subsurface features) or other governmentally
required or civil law purposes (property sales).
Earlier astronomers were able to determine longitude only by careful observation of
recurring celestial events, such as eclipses of the moons of Jupiter. Nowadays,
geodesists produce extremely precise positional data by analysing radio waves
emitted by distant stars. Once a control network is established, surveyors produce
positions using instruments that measure angles and distances between locations
on the Earth's surface.
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3. History of Surveying
 Land Surveying is one of the oldest professions in the world. The first land
surveys date back to nearly 3,000 years ago, when Egyptian Surveyors
subdivided the fertile land around the Nile River and worked on re-marking
the land after the annual flooding of the Nile River.
 The early settlement of Australia also required help from Land Surveyors. The
majority of famous early explorers including Burke and Wills had a Surveying
background and their work allowed the land to be settled, by defining
property boundaries in the city and the country. Back then Surveyors used
primitive technology including chains and steel bands, which made their
measurements difficult to record and often required the use of logarithmic
tables and slide rulers.
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4. Different types of Surveys
Geodetic SurveysCadastral Surveys
Engineering Surveys
Hydrographic Surveys
Mining SurveysAerial Surveys
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5. Measuring Angles and Distances
A standard compass can give you a rough estimate of angles, but the Earth’s
magnetic field is not constant and the magnetic poles, which slowly move over
time, do not perfectly align with the planet’s axis of rotation, because of this
true (geographic) north and magnetic north are different. Moreover, some rocks
can become magnetized and introduce subtle local anomalies when using
compass.
For this reasons Land Surveyors use transits (or their more modern equivalents,
called theodolites) to measure angles. A transit consists of a telescope for
sighting distant target objects, two measurement wheels that work like
protractors for reading horizontal and vertical angles, and bubble levels to
ensure that the angles are true. A theodolite is essentially the same instrument,
except that it is somewhat more complex and capable of higher precision. In
modern theodolites, some mechanical parts are replaced with electronics.
Traditional transit
used by surveyors
around 1948
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6. Measuring Distances
To measure distances, land surveyors once used 100-foot long metal tapes that
are graduated in hundredths of a foot. Distances along slopes were measured in
short horizontal segments. Sources of error included flaws in the tape itself, such
as kinks; variations in tape length due to extremes in temperature; and human
errors such as inconsistent pull, allowing the tape to stray from the horizontal
plane, and incorrect readings.
Surveying team measuring a baseline
distance with a metal (Invar) tape in
1916.
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7. Modern Technology
Since the 1980s, electronic distance measurement (EDM) devices have allowed
surveyors to measure distances more accurately and more efficiently than they
can with tapes. To measure the horizontal distance between two points, one
surveyor uses an EDM instrument to shoot an energy wave toward a reflector held
by the second surveyor. The EDM records the elapsed time between the wave's
emission and its return from the reflector. It then calculates distance as a
function of the elapsed time. Typical short-range EDMs can be used to measure
distances as great as 5 kilometres at accuracies up to one part in 20,000, twice
as accurate as taping.
Instruments called total stations combine electronic distance measurement and
the angle measuring capabilities of theodolites in one unit.
By using total station surveyors can calculate distances 100’s of metres away, to
centimetre accuracy. Robotic versions are also available, allowing Surveyors to
single-handedly operate a total station by remote control.
A modern total station
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8. Satellite positioning systems allow the measurement of features or
points anywhere in the world, from space. The data collected by these systems
can be used to control large infrastructure projects or provide the information
for In-car navigation systems.
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9. GIS software is used to capture and analyse data to create digital maps of
areas. The high-tech software is used to create programs such as google maps,
used by over 100 million people a month.
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10. Photogrammetry is the practice of determining the geometric properties of
objects from photographic images. This involves estimating the three
dimensional coordinates of points on an object. These are determined by
measurements made in two or more photographic images taken from different
positions. Common points are identified on each image. A line of sight (or ray)
can be constructed from the camera location to the point on the object. It is the
intersection of these rays (triangulation) that determines the three‐dimensional
location of the point.
Photogrammetry is more accurate in the x and y direction while range data is
generally more accurate in the z direction. The range data can be supplied by
techniques like LiDAR and laser scanners.
y
x
z
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11. LiDAR – Light Detection and Ranging is a method of
detecting distant objects and determining their
position or other characteristics by analysis of pulsed
laser light reflecting from their surfaces. Basically a
laser pulse is reflected from a rotating mirror inside
a laser scanner. By measuring the time delay
between when the laser pulse is emitted, and when
it returns to the scanner, the distance between the
scanner and the object can be precisely determined.
The scanner can also accurately measure angles.
NOTE: Also used for Hydrographic Surveying.
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12. Ship scanning the ocean floor Sonar image of a wreck on the ocean floor
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13. Typical scan of a pylon network (note the cables between pylons are scanned as well)VIJAY MEENA 2013BPLN037

14. Airborne LiDAR is a highly cost effective
means of collecting detailed topographic
survey information, and offers significant
advantages over traditional forms of
topographical survey in terms of speed,
access, resolution, accuracy and canopy
penetration, for a variety of applications.
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15. Some other modern techniques
3D laser scanners are used to understand and interpret the shape of things
such as buildings or land by collecting clouds of points to create digital 3-D
models. These instruments are used by surveyors to provide data to architects to
accurately visualise the land they are going to build or design on.
3D image created by a Laser ScannerVIJAY MEENA 2013BPLN037

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