Briefly explain how levelling is carried out and the formation of the collimation error. How can...

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Civil Engineering

Briefly explain how levelling is carried out and the formationof the collimation error. How can the collimation error beeliminated? Also, describe other possible sources of error inlevelling, and explain what precautions can be taken to avoid theseerrors.

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Levelling is the most widely used method of obtaining the elevations of ground points relative to a reference datum and is usually carried out as a separate procedure to those used in fixing planimetric position The basic concept of leveling involves the measurement of vertical distance relative to a horizontal line of sight Hence it requires a graduated staff for the vertical measurements an instrument that provides a horizontal line of sight Alignment axially of parts of an optical system Collimation error is due to the line of sight of a survey instrument not coinciding with traversing gear scales or leveling devices The collimation line is the line of sight passing through the intersection of the crosshairs of the reticule In differential leveling the effect of a levels collimation error can be almost entirely eliminated by carefully balancing the foresight length with the backsight length However in some settlement monitoring studies the sheer number of points or their close spacing makes such balancing impractical The following are the main sources of error in levelling 1 Instrumental Errors 2 Errors of Manipulation 3 Errors due to Settlement of Level and Staff 4 Errors due to Natural Causes 5 Common Mistake in Levelling Source 1 Instrumental Errors i Imperfect adjustment The See Answer

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