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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. Control

2. Cadastral, land, boundary, property

3. Topographic

4. Hydrographic

5. Construction

6. Aerial or photogrammetric

7. Distance

8. Angle

9. Differential

10. 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!

Data Characteristics

• Three important characteristics

1 Correct

2 Clear

3 Concise

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1. Correct

Correct means free from error.Types of errors

1. Random2. Systematic3. Natural4. Personal

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Types of Error

Random Not predictable Tend to be small and will usually cancel

themselves. Best controlled by repeating measurements.

Systematic Usually caused by damaged

equipment. Error tends to multiply (occur

for each measurement) Controlled by calibrating the

equipment.

Natural Factors in the environment

that can cause error. Must use correction values

Personal– Commonly called blunders– Controlled by following

established procedures.

What is a example of an environmental factor?

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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

Level

Vertical line

Vertical plane

Horizontal line

Horizontal plane

Level surface

Plane surveying

Geodetic surveying

Horizontal distance

Slope distance

Horizontal plane

Horizontal angle

Vertical angle

Horizontal Aero

Zenith zero

Bench mark

Elevation

Backsight

Foresight

Turning point

Balancing sights

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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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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.

Level cont.

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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

Distance--Horizontal

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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

line. Explain!

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Multiple planes

Each horizontal plane has a

unique elevation above or

below the reference

elevation.

An infinite number of planes at different elevations may exist at any point.

Is the height of the plane established by an instrument the same each time the instrument set up?

Explain!

Distance--Slope

Slope distance is a distance measured on the surface of the earth.

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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.

€

Error 1 ≠ Error 2

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Balancing Sights-cont.

When the distance from the instrument to the rod are the same for both shots, the errors cancel each other.

A error also occurs when the instrument is rotated to take the next shot.

The rod reading will be longer than it should be.

In this example because the instrument is not level, the rod reading would be shorter than it should be.

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The End