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Which is the following axis must be parallel to the line of collimation axis?
Horizontal axis
Vertical axis
Axis of altitude level
Both A and C
Axis of altitude level
In a theodolite, the axis of the altitude level (plate level for vertical circle) must be parallel to the line of collimation. This adjustment ensures that when the bubble is centered, the line of sight is truly horizontal or at a known angle, eliminating index error in vertical angle measurements.
In a theodolite, the axis of the altitude level (plate level for vertical circle) must be parallel to the line of collimation. This adjustment ensures that when the bubble is centered, the line of sight is truly horizontal or at a known angle, eliminating index error in vertical angle measurements.
╬▒indexтАЛ=╬╕measuredтАЛтИТ╬╕actualтАЛ тАФ Index error representing the angle between the line of collimation and the level axis.
The principle relies on the geometric relationship between the telescope's line of sight and the bubble tube axis. If these axes are not parallel, a vertical angle measured would include a systematic index error, equal to the angle between the two axes. Centering the bubble establishes a horizontal reference line for the telescope movement.
The line of collimation passes through the intersection of the crosshairs and the optical center of the objective lens.
The altitude level is attached to the vertical circle vernier arm.
If the adjustment is incorrect, all vertical angles measured will be consistently wrong by the constant index error.
The adjustment is typically verified by the 'Two-Peg' or similar field calibration methods.
Eliminates systematic error in vertical angle readings.
Ensures accurate height calculations during trigonometric leveling.
Requires periodic field calibration checks.
Sensitive to mechanical shocks or thermal expansion.
Trigonometric leveling.
Vertical angle measurement in surveying.
Topographic mapping.
Horizontal axis: The axis about which the telescope rotates in the vertical plane; it must be perpendicular to the vertical axis.
Vertical axis: The axis about which the theodolite rotates in the horizontal plane; it must be truly vertical during operation.
The altitude level must be parallel to the line of collimation, while the plate levels must be perpendicular to the vertical axis.
C is correct тАФ The axis of the altitude level must be parallel to the line of collimation to eliminate index error during vertical angle measurements.
Remember that 'Vertical Axis' is perpendicular to the plate levels, whereas 'Line of Collimation' is related to the altitude level for vertical precision.