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 ?