setting out simple circular curve - rankine's method of tangential deflection angles or single theodolite method
To setout the simple curve by single theodolite method.
Theodolite, Ranging rods, chain, arrows and pegs
The angle between the back tangent and the chord joining the point of commencement of the curve and the other point on the curve
1. Prepare a table of deflection angles for the first subchord,normal chord and last subchord.
2. Set up a theodolite over T1. Direct the telescope to bisect the point of intersection(B), with both plates clamped to zero.
3. Release the vernier plate and set angle 1 on the vernier using
4. Point the zero end of the tape at T1 and an arrow held at a distance C1 along it and swing the tape around T1 till the arrow is bisected by the cross hairs to fix point A.
5. Set the deflection angle .
where, d2 = 1718.9 x C2/R min., so the line of sight is along T1B
6. With zero end of the tape pinned at A and an arrow held at distance AB = C2 along it and swing the tape around A till the arrow is bisected by the cross hairs thus fixing the point B.
7. Repeat steps 5 and 6 till the last point T2 is reached.
The last point so located must coincide with the point of tangency (T2) fixed independently by measurements from the point of intersection.
The given simple curve is thus set out.