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In angular method of setting a curve, which of the following is used?
Tape
Chain
Theodolite
Compass
Theodolite
The angular method of setting out curves (such as Rankine's deflection angle method) relies on measuring horizontal angles using a theodolite ┬╖ Unlike linear methods that use tapes or chains, the angular method provides higher precision and is the standard for setting out circular curves in modern highway and railway engineering.
The angular method of setting out curves (such as Rankine's deflection angle method) relies on measuring horizontal angles using a theodolite ┬╖ Unlike linear methods that use tapes or chains, the angular method provides higher precision and is the standard for setting out circular curves in modern highway and railway engineering.
╬┤=R1718.9├ЧcтАЛ тАФ Deflection angle formula in minutes of arc
╬Ф=╧АR180LтАЛ тАФ Relation between total deflection angle and curve length
The principle involves setting the instrument at the point of curvature (PC) and measuring deflection angles to points along the curve ┬╖ The theodolite is used to set the exact angle ╬┤ calculated for each chord length c, defined by the formula ╬┤=R1718.9├ЧcтАЛ, where R is the radius of the curve in minutes of arc.
Theodolite is essential for precision measurement of angles in the field.
Angular methods are superior for long curves where linear measurements accumulate errors.
The deflection angle method is also known as Rankine's method.
Linear methods (tape/chain) are limited by terrain and cumulative tape errors.
High accuracy over long distances.
Independent of cumulative linear errors.
Ideal for complex curves and obstructed terrain.
Requires high-precision instrumentation (theodolite).
Requires skilled personnel for angle measurement and calculation.
Slower setup time compared to basic linear methods.
Railway track alignment.
Highway geometry design.
Large-scale infrastructural curve setting.
Standard value: 1 radian is approx 3438 minutes, leading to the coefficient 1718.9 for chords.
Option A and B are used for linear setting methods like the 'Offsets from long chord' or 'Successive bisection of arcs'.
Option D (Compass) is generally not precise enough for engineering curve setting.
C is correct тАФ The theodolite is the primary instrument used in the angular method for setting out curves, allowing for precise deflection angle measurements.
In exams, if the question asks for the most accurate method for long curves, always prioritize angular methods (theodolite) over linear methods (tape/chain).