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Field procedure for
setting out the curve |
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1. A theodolite is set
up at the point of curvature T1, and get it temporary adjusted.
2. The vernier A is
set to zero, and get the upper plate clamped. After opening the lower plate main screw, sight the point of intersection, V. Then the lower plate main screw gets tightened and get the point V bisected exactly using the lower plate tangent screw. Now the line of sight is in the direction of the rear tangent T1 V and the vernier A reads zero.
3. Open the upper
plate main screw, and set the vernier A to the deflection angle Da. The line of sight is now directed along the chord T1 a. Clamp the upper plate.
4. Hold the zero end
of the tape of a steel tape at T1. Note a mark equal to the first chord length C1 on the tape and swing an arrow pointed at the mark around ‘a’ till it is bisected along the line of sight. The arrow point then indicates the position of the first peg ‘a’. Fix the first peg at ‘a’.
5. Unclamp the upper
plate, and set the vernier A to the deflection angle Db. The line of sight is now directed along T1 b.
6. With the zero end
of the tape at a, and an arrow at a mark on the tape equal to the normal chord length C, swing the tape around b until the arrow is bisected along the line of sight. Fix the second peg at the point b at the arrow point.
It may be noted that
the deflection angles are measured from the tangent point T1 but the chord lengths are measured from the preceding point. thus, deflection angles observed are cumulative in nature but chord lengths swung are individual in nature.
7. Repeat steps (5)
and (6) till the last point is reached. The last point so located must coincide with the tangent point T2 already fixed from the point of intersection. |
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