Abstract: Based on the theory and method of three order B-spline modeling,the horirontal alignment oframp can be outlined in the contour map and its length and azimuthes of ternminal points can also beobtained。Then its curvature figure can be layouted by calculating curvaturee and radii of discretepoints along horizontal alignment.After the curvature flgure is medeled on the screen by using themouse,the horizontal design elements of ramp can be obtained。At last,the horizontal alignment oframp can be designed and layouted quick ly based on the unit“Ls+Ly”。

Key words: three order B-spline medeling, unit“Ls+Ly”, ramp design

摘要： 本文利用三次B样条拟合的原理与方法。在地形图上徒手绘制立交匝道平面线形的控制位置，并求出徒手线的长度与起终点的方位角，然后反算出曲线上离散点的曲率和半径，得到徒手曲线的曲率图，进而利用鼠标在屏幕上对曲率图拟合，获得立交匝道设计所需要的曲线要素，最后以“Ls+Ly”为设计单元，进行立交平面线形的设计与绘制。

关键词: 三次B样条拟合, “Ls+Ly”线元, 匝道布设