This is an engineering problem that involves geometry so I thought this would be the best forum to post in. I am attempting to interpolate elevations of roadway lines offset from a baseline (center line of a roadway) between two points. The coordinate system used is a combination of stations and offsets. In other words, the baseline is considered straight despite any curvature and the other lines that run alongside it are defined by perpendicular lines drawn from the baseline to the other lines. The offset is the distance in the x direction the point on the line is from the baseline. The station is the distance along the baseline. Unfortunately, the lines next to a baseline are often not parallel to the baseline (they sometimes curve) and in order to use a linear interpolation of elevations between two points, I first need to know the offset of points on the curve which requires an equation for the curve. I am given arc length and the offset and station of two points (which also means I know the chord length) on a line next to the baseline. Can anyone direct me to a method that uses arc length and two points to find the equation of an arc so that I can find the offset between any point on the curve and the baseline? Any help is appreciated.