Transcript 2_Principles081612

Principles of Surveying
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Surveying
The art and science of measuring and locating points and angles on,
above and below the surface of the earth.
Examples:
1.
Determine the location of points on the earth’s surface.
2.
Determine the elevation of a point.
3.
Collect data for a surface plot.
4.
Mapping the location of utilities.
5.
Calculate the distance between two points.
6.
Determine the position of boundary lines.
7.
Determine areas of tracts of land.
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Ten (10) Types of Surveys
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Control
Cadastral, land, boundary, property
Topographic
Hydrographic
Construction
Aerial or photogrammetric
Distance
Angle
Differential
Profile
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DATA
• The intended use of the data must be known before it is collected.
– Determines the equipment that should be used.
– Influences the methods that are used.
Explain!
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Data Characteristics
• Three important characteristics
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Correct
2
Clear
3
Concise
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1. Correct
Correct means free from error.
Types of errors
1.
2.
3.
4.
Random
Systematic
Natural
Personal
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Random
 Not predictable
 Tend to be small and will usually cancel
What is a example of
themselves.
an environmental
 Best controlled by repeating measurements. factor?
Natural
 Factors in the environment
Types of Error
that can cause error.
 Must use correction values
Systematic
 Usually caused by damaged
equipment.
 Error tends to multiply (occur
for each measurement)
 Controlled by calibrating the
equipment.
Personal
–
–
Commonly called blunders
Controlled by following
established procedures.
Additional Data Terms
Accuracy & Precision
– Accuracy: the number of significant digits in the measurement.
– Precision: the unit of measure.
Number one (1) rule of surveying
Incorrect data is worse than no data.
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Surveying terms.
Oblate spheroid
Horizontal angle
Level
Vertical angle
Vertical line
Horizontal Aero
Vertical plane
Zenith zero
Horizontal line
Horizontal plane
Level surface
Plane surveying
Geodetic surveying
Horizontal distance
Slope distance
Bench mark
Elevation
Backsight
Foresight
Turning point
Balancing sights
Horizontal plane
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Level
The term level is used compare the relative position of an object with the
horizon or the relative position of two or more objects.
Two objects that are level are parallel with the horizon and may or may
not be at the same elevation.
Objects that are level with each other are at the same elevation.
“Level” is usually determined by an air bubble in a small
container of liquid.
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Level cont.
The container is usually either a tube or
cylinder.
This apparatus is commonly called a spirit level or
simply a level.
The spirit level by itself is not a useable tool. It is usually incorporated with
additional tools, for example, a carpenters level, or a survey level.
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Level cont.
Objects are also level if they are perpendicular to a vertical line.
A vertical line can be established
with a plumb bob or a piece of string
with a weight.
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Distance
Two uses of distance
–Distance is the amount of separation between two points, measured along the
shortest path joining them
– The size/dimensions of an object.
When measuring the separation between points, two types of measurements
can be taken.
Horizontal
Slope
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Distance--Horizontal
A horizontal distance is a
distance measured on a
horizontal line or plane.
When would horizontal distance be used?
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Horizontal Plane
A horizontal plane is a plane that is
perpendicular to a vertical line.
The line of sight through a level
instrument forms a horizontal
Explain!
line.
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Multiple planes
An infinite number of planes at different elevations may exist at any point.
Each horizontal plane has a
unique elevation above or
below the reference
elevation.
Is the height of the plane established by an instrument the
same each time the instrument set up?
Explain!
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Distance--Slope
Slope distance is a distance measured on the surface of the earth.
Slope distance is also
called geodetic
distance.
When would slope
distance be used?
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Bench Mark
A benchmark is physical structure with a
known or assumed elevation.
It is used as the reverence point for the
survey
To be considered a benchmark the
point should be identified by a
permanent or semi-permanent
structure that will not be affected by
frost heave, traffic vibrations or
environmental changes.
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Elevation
Elevation is the vertical distance above or below a reference surface.
First common reference surface in the U.S. was the National Geodetic
Vertical Datum of 1929.
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Difference in Elevation
A difference in elevation is the
vertical distance between two
level surfaces or planes.
When the elevation of each of the level surface or plane is known, the
difference in elevation can be calculated between the earth and any level
surface or plane.
The difference in elevation can also be determined between any two
surfaces or planes.
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Backsight
Def: A back sight is a rod reading taken on a point of known, or assumed
elevation.
Backsights are
usually used to
establish the height
of the instrument.
Instrument height = Elevation + Rod reading
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Foresight
A foresight is a rod reading taken on a point with unknown elevation.
It is used to determine the elevation.
Elevation can be
actual or relative.
Elevation = Instrument Height - Rod Reading
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True vs. Intermediate Foresights
In surveying two different types of foresights are used, intermediate,
and true.
An intermediate foresight is a rod reading on a point that will not be
used as a turning point or benchmark.
A true foresight is a rod reading on an point that will be used for a
turning point or for a benchmark.
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Turning Point
A turning point (TP) is a temporary benchmark.
The purpose of the turning point is to provide a continuous reference point
for the height of the instrument when it is moved.
Because it is a temporary benchmark, a turning point must be
established on an object with stable elevation.
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Facts About Turning Points
The turning point should be a stake or other durable structure.
– If the turning point is not at the earths surface, the elevation of that station
can not be used during design.
– When the turning point is on the surface, the elevation can be used.
The TP becomes a new point that can be used as a reference point.
Turning points are intended to be temporary. Only used during the life of
the survey.
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Balancing the Sights
Balancing the sights refers to setting the instrument 1/2 way
between the two stations.
This reduces the chance of the error that occurs if the instrument
is not level.
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Unbalanced Sights
If the instrument is not level,
the rod readings will be
incorrect.
In the illustration the reading
will be greater than it should
be.
An error will also occur
when the instrument is
rotated to the second sight.
Because the instrument is a
greater distance from the
rod, the error will be greater.
Error1  Error2

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Balancing Sights-cont.
In this example because the
instrument is not level, the
rod reading would be
shorter than it should be.
 A error also occurs when
the instrument is rotated to
take the next shot.
 The rod reading will be
longer than it should be.
When the distance from the instrument to the rod are the same for
both shots, the errors cancel each other.
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The End
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