10.4.1 Offsets from the Tangent

The position of the curve (in Figure 10.16) is located by right-angled offsets Y set out from distances X, measured along each tangent, thereby fixing half the curve from each side.

Figure 10.16: Offsets from the tangent

The offsets may be calculated as follows for a given distance X. Consider offset Y ₃, for example.

Thus for any offset Y _i at distance X _i along the tangent:

(10.7)

10.4.2 Offsets from the Long Chord

In this case (Figure 10.17) the right-angled offsets Y are set off from the long chord C, at distances X to each side of the centre offset Y ₀.

Figure 10.17: Offsets from the long chord

An examination of Figure 10.17, shows the central offset Y ₀ equivalent to the distance T ₁ A on Figure 10.16; thus:

Similarly, DB is equivalent to DB on Figure 10.16, thus: DB = and offset Y ₁ = Y ₀ - DB ? Y ₁ = and for any offset Y _i at distance X _i each side of the mid-point of T ₁ T ₂:

(10.8)

Therefore, after computation of the central offset, further offsets at distances X _i