Distance Measuring

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Distance Measuring
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Two principles of measuring distance

• 1) It takes two points to form a line.
• 2) The shortest distance between two points is a
  straight line.

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Distance

• In surveying, the term distance has two uses.
• The common use is to measure the displacement
  (distance) between two or more points.
• Distance can also be used to define the
  dimensions of an object

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Best method

• Determined by
• Environment
• Use of the data
• Equipment available
• Expertise of individuals

• Personal preference
• Topography
• Client specifications
• Regulations
• Standard practice

The most important factor is the use of the data.
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Example

• What method should be used to determine the
  amount of materials needed to build a fence?

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Barbed Wire

• Barbed wire is usually purchased in rolls that
  contain 100 rods of wire.
• Does the precision need to be 1/100s of a foot?
• No

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Wooden Pole

• Horizontal poles are usually six to eight feet.
• Is pacing an acceptable method?
• Yes

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Foundation

• Measuring the location of forms for a foundation
  is a different job.
• Distances should be measured to 1/8 or 1/4 inch.

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Horizontal Slope Distance

• Horizontal distance is a distance measured on a
  horizontal plane.
• Horizontal distance can also be calculated.
• Slope distance is a distance measured on a
  surface that is not a plane.
• For general surveying the difference between
  horizontal and slope distance is ignored for
  slopes less than 5.

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Difference Between Horizontal and Slope Distance

• The illustration shows the difference that occurs
  for a 3 slope.
• The actual difference in length is

When the slope is 3, the difference between
slope distance and horizontal distance is 0.05
feet per 100 feet.
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Horizontal Distance

• To measure horizontal distance, the tape must be
  on a horizontal plane.
• The earth surface is seldom a horizontal plane.

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Slope distance

• When distance is measured on the surface of the
  ground it is called slope (surface) distance.

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Determining Horizontal Distance

• The surveyor has two choices.
• Use equipment and techniques to measure
  horizontal distance.
• Measure slope distance and collect additional
  information to calculate horizontal distance.

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Using Equipment To Measure Horizontal Distance

• Chain, level and plumb bob.

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Using Equipment To Measure Horizontal
Distance--Stadia

• Stadia distance is a horizontal distance because
  a level instrument is used to collect the data.

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1/2 Stadia
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Using Equipment To Measure Horizontal
Distance--(EDM)

• An EDM measures distance by determining the
  amount of time required for a signal to leave the
  instrument, reflect off of the target, or object,
  and return.
• If the instrument is level when the measurement
  is taken, the measurement is horizontal distance.

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Calculating Horizontal Distance

• To calculate horizontal distance you must know
  the slope distance and one additional bit of
  information for each station. Either
• slope
• or
• Change in elevation
• or
• Vertical angle.

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Calculating Horizontal Distance --Percent slope
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Calculating Horizontal Distance--Difference in
Elevation
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Calculating Horizontal Distance--Vertical Angle
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Questions ?