GATE CE 2026 Set 1 — Question 35
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Geomatics Engineering → Levelling → Height of Instrument Method
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Question
The height of the plane of collimation of a levelling instrument is 100.000 m from a datum. The levelling instrument measures a Back Sight of 1.500 m on a vertically held staff at a ground point . The reduced level (in m) of the ground point with respect to the datum is ________________ (rounded off to three decimal places).
Correct answer
98.5 to 98.5
Solution
The Reduced Level (RL) of a point can be calculated from the Height of Instrument (HI) or Plane of Collimation using the formula:
Given:
Height of the plane of collimation () = 100.000 m
Staff reading at point (Back Sight, ) = 1.500 m m.
Given:
Height of the plane of collimation () = 100.000 m
Staff reading at point (Back Sight, ) = 1.500 m m.
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