Setting Out Simple Circular Curves

Setting out a simple circular curve involves marking points on the ground so that they form part of a circle with a specific radius. There are various methods to achieve this, broadly classified into linear methods and angular methods.

Linear methods rely primarily on measuring distances (linearly) from known points or lines (like tangents or chords) to locate points on the curve. Angular methods use instruments like a theodolite to measure angles in conjunction with linear measurements (like chord lengths).

The question asks which method is NOT a linear method for setting out a simple circular curve. Let's examine the given options:

• By offsets from tangents: This is a standard linear method. Points on the curve are located by measuring distances along the tangent (tangent distances) and then measuring perpendicular or radial offsets from these points to the curve.
• By ordinate or offsets from the long chord: This is also a standard linear method. Points on the curve are located by measuring distances along the long chord and then measuring perpendicular offsets (ordinates) from these points to the curve.
• By successive bisection of arcs: While bisection can lead to linear measurements (like halving chord lengths), the phrase "bisection of arcs" conceptually relates to dividing the curve length itself. In practice, methods based on dividing the curve often translate back to linear measurements using chords and mid-ordinates, making the *field application* typically linear. However, comparing it to the clearly non-standard first option, this method, if interpreted as geometrically dividing the arc length, isn't a direct linear measurement technique like offsets from tangents or long chord unless further specified how the points are physically set out. But option 1 is unequivocally not a standard method.
• By moving average of arc radius: This method is not a recognized or standard method for setting out a simple circular curve. For a simple circular curve, the radius is constant, not variable or subject to a "moving average". Therefore, this concept does not represent a valid technique, linear or otherwise, for setting out such a curve.

Based on the analysis, "By moving average of arc radius" is not a linear method, nor is it a valid method at all, for setting out a simple circular curve.