Compute the elevation at any point on a vertical curve from the grade and curve length.
输入前坡 g₁、后坡 g₂、曲线长 L 与距起点距离 x，求相对高程 y。
| Item | Formula / Note | Source / Standard |
|---|---|---|
| Vertical curve equation | For a parabolic vertical curve: y = x^2/(2R), where x is the distance from the start | JTG D20-2017, Design Specification for Highway Alignment |
| Expressed by gradient difference | y = (i1 - i2) · x^2/(2L), where L is the vertical curve length | JTG D20-2017, Design Specification for Highway Alignment |
| Vertical curve elements | Key elements are radius R, curve length L, tangent T and external distance E | JTG D20-2017, Design Specification for Highway Alignment |
| Design elevation | Design elevation = gradient elevation ± vertical curve correction (minus for crest, plus for sag) | JTG D20-2017, Design Specification for Highway Alignment |