I am trying to solve this issue, where a S-bend is designed using FDTD tools from Lumerical. It takes poles as input so there is no any information about the length. However, we can set the height and the straight length between the ends. I found that they implement Bezier curves for the generation of bends.

My question is how to determine the exact length of the S- bend?

Please refer to the figure to understand the structure. I want to calculate the length marked by yellow lines.