Ground Survey and Positioning

Chapter 7

 

Given a triangle with side A= 10 m and side B= 20 and the angle between them = 37 degree. Find the length of the other side and the other two angles (refer to page 117)

 

List the common methods used for distance measurement?

  (Pacing, Odometers, Tachymetry, Chaining, EDM)

 

Discuss briefly the principles of Electronic Distance Measuring (EDM)

EDM is based on the use of light waves, electromagnetic waves, infrared, or even lasers for measuring distance in comparison

Distance = speed of light X time

Although some of these waves are affected by changes in temperature, pressure, and humidity, the effects are small and can be corrected

EDM is useful for measuring distances that are difficult of access (river, lake, highway)

 

List the devices that used for angle measurement

Sextant (Obsolete)

Transit (Obsolete)

Magnetic Compass

Theodolite (page 119)

 

Discuss briefly “Traverse”, illustrate by figure?

 

Traverse may be defined as a series of successive straight lines that are connected together (boundary of land, railroad)

Distances (Tape, EDM) and angles of the traverse must be measured

An interior, exterior, or deflection angle can be used in traversing

If the bearing of one side of a traverse has been determined and the angles between the sides have been measured, the bearing of the other sides can easily be calculated (Draw Figure  7.5 Page: 120)

 

Given a figure with coordinates (100,400), (600,800), (900,300), and (500,100), find its area ? Hint: use (2A = summation of the solid lines products minus summation of the dashed lines products)

 

 

What is meant by an elevation of a point and why is it important?

The elevation of a point is the vertical distance above or below a reference level surface (normally, mean sea level -MSL).

Elevation is very important in different applications such as construction, geology, farming, and drainage (contour maps)

 

List and define the main types of Levelling?

Trigonometric: Horizontal distance and vertical angle are measured and used to compute elevation differences

Barometric: Determination of elevation by measuring changes in air pressure using altimeters

Spirit (direct levelling): Is the usual way of levelling. Vertical distances are measured in relation to a horizontal line, and these values are used to compute the differences in elevations between various points