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Formula reference
Approximate (standard track measurement, valid when v « R):
R = c² / (8v) v = c² / (8R) c = √(8Rv)
Exact (geometric):
R = (c²/4 + v²) / (2v) v = R − √(R² − (c/2)²) c = 2√(2Rv − v²)
Degree of curvature (degrees per 20 m chord):
D = 1719.6 / R