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What is said when vertical circle is to the left of the observer ?
Face left
Telescope normal
Inverted telescope
Both A and B
Both A and B
When the vertical circle of a theodolite is to the left of the observer while sighting an object, the observation is termed as 'Face Left'. This state is equivalent to the 'Telescope Normal' position, where the vertical circle is on the left and the bubble of the plate level is generally kept upward.
When the vertical circle of a theodolite is to the left of the observer while sighting an object, the observation is termed as 'Face Left'. This state is equivalent to the 'Telescope Normal' position, where the vertical circle is on the left and the bubble of the plate level is generally kept upward.
Face┬аLeft+Face┬аRight=360┬░ тАФ Relationship used to eliminate index error in vertical angles
Total┬аAngle=2Face┬аLeft+(FaceRight┬▒180┬░)тАЛ тАФ Mean horizontal angle calculation
The face of the theodolite is defined by the position of the vertical circle relative to the observer's line of sight. By standard convention, when the vertical circle is to the observer's left, the instrument is in the normal orientation. Rotating the telescope by 180 degrees about the horizontal axis places the vertical circle to the right, which is termed 'Face Right' or 'Telescope Inverted'.
Face Left is the primary position for initial setup.
Telescope Normal means the vertical circle is on the left and the telescope is not inverted.
Face Right is obtained by revolving the telescope 180 degrees.
Switching faces is essential to eliminate instrumental errors like collimation error.
Eliminates instrumental errors
Increases precision of measured angles
Takes more time to perform two sets of readings
Increases manual computational effort
Triangulation surveys
Precise leveling and angle measurement
Calibration of surveying instruments
| Feature | Face Left (Normal) | Face Right (Inverted) |
|---|---|---|
Vertical Circle Position | Left of Observer | Right of Observer |
An error in the reading due to the non-perpendicularity of the horizontal axis and the line of collimation is eliminated by taking both face readings.
Option C is the opposite of the condition described; in an inverted telescope, the vertical circle is to the right.
D is correct тАФ When the vertical circle is on the left, the instrument is defined as being in Face Left, which corresponds to the Telescope Normal condition.
Always remember that taking the mean of Face Left and Face Right observations cancels out most systematic errors inherent in the theodolite's mechanical adjustments.
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