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In modern theodolite, centering of theodolite is done by ______.
Optical plummet
Plumb bob
Foot screw
Stone
Optical plummet
In modern surveying, centering of a theodolite is the process of setting the instrument exactly over a survey station mark. An optical plummet uses a built-in optical system to sight the ground point vertically through the instrument's center, replacing the traditional swinging plumb bob.
In modern surveying, centering of a theodolite is the process of setting the instrument exactly over a survey station mark. An optical plummet uses a built-in optical system to sight the ground point vertically through the instrument's center, replacing the traditional swinging plumb bob.
╬Фx=xiтАЛтИТxsтАЛ тАФ Error in centering defined by the distance between instrument vertical axis xiтАЛ and station mark xsтАЛ
The optical plummet contains a small prism or mirror that reflects the line of sight 90 degrees downward through the vertical axis of the theodolite. The user looks through the optical plummet eyepiece and adjusts the tripod or shifting head until the reticle crosshair coincides precisely with the station mark on the ground.
Optical plummet is unaffected by wind, unlike a physical plumb bob.
The optical plummet is built into the tribrach or the main body of the theodolite.
Centering and leveling are sequential operations performed during the temporary adjustment of the instrument.
Modern digital theodolites and Total Stations almost exclusively use optical or laser plummets.
Faster setup time
High precision in windy conditions
No mechanical vibration or oscillation
Requires maintenance of internal optics
More expensive than a simple plumb bob
Theodolite leveling and setup
Total Station orientation
Precision surveying
| Feature | Optical Plummet | Plumb Bob |
|---|---|---|
Accuracy | High | Medium/Low |
Wind Sensitivity | None | High |
The plumb bob (Option B) is the traditional method but is slow and prone to errors due to wind or breeze.
Foot screws (Option C) are used for leveling the instrument, not for centering.
A stone (Option D) is irrelevant to instrument centering.
A is correct тАФ Optical plummet allows for accurate and rapid centering by sighting the ground point directly through the vertical axis of the theodolite.
Always ensure the tribrach is level before finalizing centering; if the instrument is not level, the optical plummet will not be looking vertically downwards.
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