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Which axis is known as when theodolite is rotated in a horizontal plane ?
Horizontal
Vertical
Axis of bubble
Trunnion
Vertical
In a theodolite, the axis about which the instrument rotates in a horizontal plane is known as the vertical axis. This axis remains perpendicular to the horizontal plate (azimuth plate) and serves as the pivot for measuring horizontal angles.
In a theodolite, the axis about which the instrument rotates in a horizontal plane is known as the vertical axis. This axis remains perpendicular to the horizontal plate (azimuth plate) and serves as the pivot for measuring horizontal angles.
Horizontal Angle=θfinal−θinitial — The basis for horizontal angle measurement using vertical axis rotation
The vertical axis is defined as the line passing through the center of the ball-and-socket joint of the leveling head. When the theodolite is properly leveled, this axis is made truly vertical (coincident with the gravity line). Any rotation about this axis allows the telescope to sweep across the horizontal plane, enabling the measurement of horizontal angles between sighted stations.
The vertical axis is the primary reference line for horizontal measurements.
Correct leveling of the instrument ensures the vertical axis is perfectly plumb.
Horizontal rotation is controlled by the upper and lower clamp/tangent screws.
Precise measurement of horizontal angles.
Allows for systematic orientation during traverse surveying.
Sensitivity to leveling errors.
Mechanical wear on the vertical spindle can lead to centering errors.
Triangulation and Traversing.
Laying out horizontal curves in highway/railway engineering.
The horizontal axis, often called the trunnion axis, is the axis about which the telescope rotates in the vertical plane (for altitude angles).
Axis of bubble refers to the line tangent to the center of the bubble tube, which must be horizontal when the bubble is centered.
B is correct — The vertical axis is the axis of rotation for measuring horizontal angles in a theodolite.
Remember that the 'Vertical Axis' is for horizontal angles, while the 'Horizontal Axis' (Trunnion axis) is for vertical angles; this is a common trap in competitive exams.
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