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Surveying 0

Levelling

QuestionAnswer
What is Levelling? Levelling is the measurement process to determine height and producing heights on map, ensure construction at correct height or gradient. enables horizontal distance to be calculated.
What are the Principles of surveying? To measure the difference in height between two points, and if the height of one point is known, then the height of the other can be determined by applying the difference in height between the two points.
What is Level Line? A line that is at a constant height relative to mean sea level.
Define Datum? A level line is chosen to which the elevation of all points are related. In U.K chosen datum is M.S.L at Newlyn Cornwall.
What is a Horizontal Line? Line tangenital to the level line at any particular point.
What is Line of Collimation? This is the line of sight of the instrument - horizontal line joining the centre of the object lens to the centre of the reticule. when the telescope is rotated it will sweep out a horizontal plane of collimation.
Define Reduced Level! Height of a Point relative to the chosen datum.
What are Bench Marks! These are Reference marks or points, the reduced levels of which have been accurately determined by levelling.
Name and Explain the types of Bench marks. O.B. (Ordnance Bench Marks)- established on Ordnance from datum at Newlyn, Cornwall. T.B.M (Temporary Bench Marks) - set up on stable points near construction sites where no O.B.M is found.
What are the reasons for midway position? Curvature of the earth Colimation error - line of sight not horizontal.
What is a Back-sight? First Reading/Sight taken for a given instrument position.
What is Foresight? Last reading/sight taken before instrument is moved to next position. Hint always work to 3 decimal places.
CALCULATION EQUATIONS FOR RISE AND FALL METHOD? B.S - Back sight F.S - Foresight Rise/Fall = Bs - Fs. Reduced Level(b) = RL(a)+(Bs - Fs)
CALCULATION EQUATIONS FOR HEIGHT OF COLLIMATION METHOD? B.s - Back sight F.s - Fore sight Reduced Level(b) = (RL(a)+Bs) -Fs Height of Collimation - (RLa+Bs)
Created by: frantost
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