principles of land measurement & surveying 2003

8/13/2019 Principles of Land Measurement & Surveying 2003

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Principles of Land

Measurement &Surveying

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The artand scienceof measuring and locatingpoints and angles on, above and below the

surface of the earth.

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Surveying

Examples:

1. Determine the location of points on the earths 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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1. Control

2. Cadastral, land, boundary,property

3. Topographic4. Hydrographic

5. Construction

6. Aerial or photogrammetric

7. Distance8. Angle

9. Differential

10. Profile

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Ten (10) Types of

Surveys


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DATA

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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.

Two important characteristics

Integrity

Correct

Integrity: an unimpaired condition; soundness

Correct: performing to an approved or

conventional standardWhat is the standard for surveying?

59 O.S. 471.1 et seq, Chapter 245:15-13-2.


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Types of errors

1. Random2. Systematic

3. Natural

4. Personal

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)

Best control is calibration of

equipment.

Natural Factors in the environment that

can cause error. Curvature

Refraction

Must use correction values

Personal Commonly called blunders

Best controlled by following

established procedures.


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Additional Data Terms

Accuracy & Precision

Accuracy: the number of significant digits in themeasurement.

Precision: the unit of measure.

Number one (1) rule of surveying

Incorrect data is worse than no data.


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Surveying terms.

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Level

Vertical line

Vertical plane

Horizontal line

Horizontal plane

Level surface

Plane surveying

Geodetic surveying

Horizontal distanceHorizontal plane

Horizontal angle

Vertical angle

Horizontal Aero

Zenith zero

Bench markElevation

Backsight

ForesightTurning point

Balancing sights


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The term level is used compare the relative position of an objectwith the horizon or the relative position of two or more objects.

Two objects that are level are parallel with the horizon and mayor not be at the same elevation.

Objects that are level with each other are at the same elevation.

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Level

Level is usually determined by an air bubble in a smallcontainer of liquid.


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Level cont.

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The container is usually either a tube or

cylinder.

This apparatus is commonly called a spirit level orsimply 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.

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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 is the amount of separation betweentwo points, measured along the shortest path

joining them or the size of an object.

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Horizontal Distance

A horizontal distance

is a distance measured

on a horizontal line or

plane.


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A horizontal plane is a plane that

is perpendicular to a vertical line.

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Horizontal Plane

The line of sight through a level

instrument forms a horizontal

line.


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Multiple planes

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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.


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A benchmark is physical

structure with a known orassumed elevation.

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Bench Mark

To be considered a benchmark

the point should be identified bya permanent or semi-permanentstructure that will not beaffected by frost heave, trafficvibrations or environmental

changes.

Surveying standards havevery specific guidelines onthe required structure for

benchmarks.


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The most commonly used reference level surface in the

U.S. is the National Geodetic Vertical Datum of 1929.

Established by connecting 26 tidal benchmarks along the

Atlantic, Gulf of Mexico and Pacific Coasts, this datum is

the zero elevation reference point used for surveying.

Because GPS surveying uses multiple reference

surfaces, the desired reference surface must be specified.

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Elevation Elevation is the distance above or

below a reference level surface.


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A difference in elevation is the vertical

distance between two level surfaces or planes.

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Difference in Elevation

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.


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A back sight is a rod reading taken on apoint of known, or assumed elevation.

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Backsight

Backsights areusually used toestablish the height

of the instrument.

Instrument height = Elevation + Rod reading


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A foresight is a rod reading taken on a point with unknown elevation.

It is used to determine the elevation.

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Foresight

Elevation can beactual or relative.

Elevation = Instrument Height - Rod Reading


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In surveying two different types of foresights are used,

intermediate, and true.

An intermediate foresight is a rod reading on a point

that will notbe 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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True vs. Intermediate

Foresights


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A turning point (TP) is a temporary benchmark.

The purpose of the turning point is to provide a continuousreference point for the height of the instrument when it ismoved.

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Turning Point

Because it is a temporary benchmark, a turning point must beestablished on an object with stable elevation.


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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 notbe used during design. When the turning point is on the surface, the elevation canbe

used.

The TP becomes a new point that can be used as a referencepoint.

Turning points are intended to be temporary. Only used during thelife of the survey.

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Facts About Turning Points


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Balancing the Sights

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Balancing the sights refers to setting the instrument 1/2 waybetween the two stations.

This reduces the chance of the error that occurs if the instrument

is not level.


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Unbalanced Sights

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If the instrument is not level,

the rod readings will beincorrect.

In the illustration the reading

will be greater than it should

be.

An error will also occurwhen the instrument isrotated to the second sight.

Because the instrument isa greater distance from therod, the error will be greater.

Error1 Error

2


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Balancing Sights-cont.

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In this example because

the instrument is not level,the rod reading would be

shorter than it should be.

A error also occurswhen the instrument isrotated to take the nextshot.

The rod reading will belonger than it shouldbe.

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


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