Rankine's method or tangential angle method is an angular technique for laying out circular curves by a combination of chaining and angles at circumference, fully exploiting the theodolite and making a substantial improvement in accuracy and productivity over existing methods.
This method requires access to only one road/path of communication to lay out a curve.
Points on curve are calculated by their angular offset from the path of communication.
He had been working on railways in Ireland, on the construction of the Dublin and Drogheda line.
This method makes sure that any line drawn from the known tangent to curve is a chord of the curve by constraining the deflection angle of line.
[1] Let AB be a tangent line/path of communication or start of a curve, then successive points on the curve can be obtained by drawing an arbitrary line of length
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