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Distance Measuring. 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. . Distance. In surveying, the term “distance” has two uses.
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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.
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
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.
Example • What method should be used to determine the amount of materials needed to build a fence?
Barbed Wire • Barbed wire is usually purchased in rolls that contain 100 rods of wire. • Does the precision need to be 1/100’s of a foot? • No
Wooden Pole • Horizontal poles are usually six to eight feet. • Is pacing an acceptable method? • Yes
Foundation • Measuring the location of forms for a foundation is a different job. • Distances should be measured to 1/8 or 1/4 inch.
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%.
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.
Horizontal Distance • To measure horizontal distance, the tape must be on a horizontal plane. • The earth surface is seldom a horizontal plane.
Slope distance When distance is measured on the surface of the ground it is called slope (surface) distance.
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.
Using Equipment To Measure Horizontal Distance • Chain, level and plumb bob.
Using Equipment To Measure Horizontal Distance--Stadia Stadia distance is a horizontal distance because a level instrument is used to collect the data.
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.
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.