iPOGO - 10 Chord Spiral Curve Calculator

Example with formulas:
 Given Ls=200.0, Total Delta=2°51', Dc=0.75° chord definition
 1) radius of simple curve 
      Rc = 50 / sin(Dc/2) = 7639.49181 feet
 2) total spiral delta 
      SD = (LS*Dc) / 200 = 0.75°
 3) length along original tangent to offset at end of spiral 
       X = Ls - (Ls^3 / 40 * Rc^2) = 199.996573 feet
 4) perpendicular offset from original tangent to end of spiral
       Y = Ls^2 / (6 * Rc) = 0.872658 feet
 5) throw distance from original curve to end of spiral
       O = Y - (Rc * (1 - cos(SD))) = 0.21816 feet
 6) distance from OFFSET T.C. to T.S.
      Xo = X - (Rc * Sin(SD)) = 99.998715 feet
 7) tangent length of original curve
      Tc = Rc * Tan(TotalDelta/2) = 190.04054 feet
 8) tangent length from original PI to TS
      Ts = Xo + Tc + (O * Tan(TotalDelta/2)) = 290.0447 feet
 9) tangent length from original TC to TS
      TcTs = Xo + (O * Tan(TotalDelta/2)) = 100.0041 feet
 10) spiral chord length
      Sc = (X^2 + Y^2)^0.5 = 199.998477 feet
 11) rate of change in radius
       a = 100 * (Dc / Ls) = 0.375° per 100 feet