leveling
chapter seven
The Theory Of Differential Leveling
The illustration shows the typical leveling process that is repeated time and again to transfer an elevation from one point to another. The known elevation is transferred up to the line of sight by reading the backsight. By definition, the line of sight is horizon-tal; therefore, the line of sight elevation can then be transferred down to the unknown elevation point by reading the foresight.
Transferring the Elevation to the HI
In this illustration, the elevation where the rod is held is known. That elevation is transferred vertically to the line of sight by reading the rod. By adding the known elevation and the backsight reading, the height of instrument can be determined. The formula for this is shown as:
Transferring the HI to the Turning Point
In the illustration here, the elevation of the HI is known. That elevation is transferred vertically down to the point on the ground by reading the rod. By subtracting the HI and the foresight reading, the elevation of the point on the ground can be determined. The formula for this is shown as: