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A stadia telescope, in a tacheometer, is fitted with
two additional vertical hairs
two additional horizontal hair
both A and B
None of the above
two additional horizontal hair
A tacheometer is a specialized transit theodolite fitted with a stadia diaphragm. A stadia telescope contains a diaphragm provided with two additional horizontal hair readings, known as upper and lower stadia hairs, placed equidistant from the central horizontal cross-hair.
A tacheometer is a specialized transit theodolite fitted with a stadia diaphragm. A stadia telescope contains a diaphragm provided with two additional horizontal hair readings, known as upper and lower stadia hairs, placed equidistant from the central horizontal cross-hair.
D=KS+C тАФ Horizontal distance formula in tacheometry
K=ifтАЛ тАФ Multiplying constant (typically equal to 100)
C=f+d тАФ Additive constant (0 for an anallactic lens)
In stadia tacheometry, the vertical distance (intercept) on a graduated staff intercepted between the two outer stadia hairs is measured. Using the optical properties of the telescope, the horizontal distance between the instrument station and the staff is computed using the formula D=KS+C, where the staff intercept S is directly proportional to the distance.
The stadia diaphragm features two additional horizontal hairs placed symmetrically above and below the main central horizontal hair.
The spacing between the upper and lower stadia hairs (i) remains fixed in fixed-hair tacheometry.
The ratio of focal length f to stadia spacing i gives the multiplying constant K, usually designed to be 100.
Eliminates the need for chaining or taping on rough or inaccessible terrain.
Rapid optical distance measurement for surveying and contouring.
Less accurate than precision taping or Electronic Distance Measurement (EDM).
Observational errors increase significantly at long sight distances.
Preparation of topographic maps and contour surveys.
Location surveys for roads, railways, and reservoirs in hilly regions.
Standard values for constants: K=100 and C=0 (when an anallactic lens is used).
Option A is incorrect because additional vertical hairs are not used for stadia distance measurement.
Option C is incorrect as additional vertical hairs are not fitted for stadia measurement.
B is correct тАФ A stadia telescope is provided with two additional horizontal hairs placed symmetrically above and below the central horizontal cross-hair to take staff intercept readings.
Remember that anallactic telescopes fit a special internal convex lens (anallactic lens) which reduces the additive constant C=(f+d) strictly to zero, simplifying field computations.