Hi, guys, I'm making a procedural modeling of a roller coaster. It looks very common, but I'm stuck in a problem.

After I create a curve, I want to use the parallel transport method to get a smooth orientation, but I find that I do get smooth normal, tangent and bitangent, but I can't smooth them where the ends of the curve are connected.

I mean, if I rotate and translate to the last point based on the normal of the first point, I will not get a smooth orientation where the last point meets the first point (I find that almost all the situations discussed in the tutorial are based on an unclosed curve, and I want to make a closed curve here, I wonder if there is a solution.)

As shown in the figure below, there is a smooth orientation in other parts of the curve, except where the curve is connected end to end.