1. Distance Measuring

2. 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.

3. 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

4. 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.

5. Example  What method should be used to determine the amount of materials needed to build a fence?

6. 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

7. Wooden Pole  Horizontal poles are usually six to eight feet.  Is pacing an acceptable method?  Yes

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

9. 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%.

10. 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.

11. Horizontal Distance  To measure horizontal distance, the tape must be on a horizontal plane.  The earth surface is seldom a horizontal plane.

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

13. 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.

14. Using Equipment To Measure Horizontal Distance  Chain, level and plumb bob.

15. Using Equipment To Measure Horizontal Distance--Stadia Stadia distance is a horizontal distance because a level instrument is used to collect the data.

16. 1/2 Stadia

17. 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.

18. 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.

19. Calculating Horizontal Distance --Percent slope

20. Calculating Horizontal Distance--Difference in Elevation

21. Calculating Horizontal Distance--Vertical Angle

22. Questions ?