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CivilAdvanced Survey
PrevNext

Horizontal axis is also called _______.

A

Vertical Axis

B

Outer Axis

C

Trunnion Axis

D

Line of sight

Correct Answer

тЪЩя╕П TE тАв Technical Concept & PrincipleCivilAdvanced Survey
Option C

Trunnion Axis

Quick Summary:

In a theodolite, the horizontal axis is the axis about which the telescope rotates in the vertical plane. It is technically referred to as the trunnion axis because the telescope is supported by trunnions resting on the standards of the instrument.

тЪЩя╕ПTETechnical SolutionConcept & Principle
ЁЯТб Explanation

In a theodolite, the horizontal axis is the axis about which the telescope rotates in the vertical plane. It is technically referred to as the trunnion axis because the telescope is supported by trunnions resting on the standards of the instrument.

ЁЯФв Key Formulas

e=VтИТ(H┬▒╬╕)e = V - (H \pm \theta)e=VтИТ(H┬▒╬╕) тАФ represents the error due to non-perpendicularity of the trunnion axis to the vertical axis, where eee is the error, VVV is the vertical angle, and HHH is the horizontal axis inclination.

тЪЩя╕П Working Principle

The trunnion axis allows the telescope to perform 'transiting' or 'plunging'. It must be perfectly perpendicular to the vertical axis of the theodolite to ensure accurate vertical angle measurements and to prevent collimation errors during telescope rotation.

ЁЯУМ Key Points
  • тЦ╕

    The horizontal axis is also known as the trunnion axis.

  • тЦ╕

    It must be perpendicular to the vertical axis for precise measurements.

  • тЦ╕

    Adjustments to this axis are performed to eliminate 'horizontal axis error'.

  • тЦ╕

    It is the axis about which the telescope moves when measuring vertical angles.

тЬЕ Advantages
  • тЦ╕

    Allows for full rotation of the telescope (transiting).

  • тЦ╕

    Essential for defining the vertical plane in geodetic surveying.

тЭМ Disadvantages / Limitations
  • тЦ╕

    Susceptible to mechanical wear leading to instrument error.

  • тЦ╕

    Requires periodic calibration to maintain perpendicularity with the vertical axis.

ЁЯЫая╕П Applications / Uses
  • тЦ╕

    Measuring vertical angles in topography.

  • тЦ╕

    Controlling vertical alignment in civil engineering projects.

  • тЦ╕

    Determining heights and elevation differences via trigonometric leveling.

ЁЯУД Additional Information
  • тЦ╕

    The Vertical axis is the axis about which the theodolite rotates in the horizontal plane.

  • тЦ╕

    The Line of Sight (Line of Collimation) is the line passing through the optical center of the object glass and the intersection of the crosshairs.

  • тЦ╕

    Option D (Line of sight) refers to the optical axis, not the mechanical support axis.

ЁЯУК Diagram / Illustration
Theodolite Axis DefinitionsHorizontal (Trunnion) AxisVertical Axis
тЬЕ

C is correct тАФ The horizontal axis is technically termed the trunnion axis as it supports the telescope on the standards.

Core Concepts Used
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Theodolite Instrumentation Geodetic Surveying Instrument Calibration
ЁЯТб EXAM TIP

Always remember that in surveying instruments, axes are defined by their physical rotation function; the horizontal axis rotates the telescope vertically, while the vertical axis rotates the whole head horizontally.

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