distance measuring. two principles of measuring distance 1) it takes two points to form a line. 2)...
TRANSCRIPT
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.
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:
€
% Slope =riserun
100x
Rise =% slope
100 x run = 0.03 100x = 3
€
a2 = b2 + c2
b = a2 −c2
= 100 2 −32
= 99.95When 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.
1/2 Stadia
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.
Calculating Horizontal Distance --Percent slope
€
% Slope =RiseRun
100x
Rise =% Slope x Run
100
=2 255.30 x ft
100= 5.11 ft
€
a2 = b2 + c2
b = a2 −c2
= 255.30 2 −5.11 2 = 255.25 ft
Calculating Horizontal Distance--Difference in Elevation
€
a2 = b2 + c2
b = a2 −c2
= 234.5 2 −6.5 2 = 234.41 ft
€
Cosin θ =adjhyp
adj = Cosin θ x hyp
= 19.2 510.17 Cosin x ft
= 0.9444 510.17x
= 481.79 ft
Calculating Horizontal Distance--Vertical Angle
Questions ?