GetPerpendicularFrames as releative position not absolute

I am writing C# code in grasshopper.

I have the following line of code:

Plane[] frames = curve.GetPerpendicularFrames(new double[]{0,1.0});

I would expect this to put a frame at the beginning and end of the line. Instead, it puts a frame at the beginning and another 1mm down the line. How do I get relative position instead of absolute position for GetPerpendicularFrames?

interesting, I also tried {0, GetLength(curve)} and it places it at the beginning and the midpoint. The only way I could get it to work was {0, GetLength(curve) * 1.99}. What is going on?

Either change domain to interval 0 1, or use curve.Domain.T1