This post is related to another one.

I am comparing results obtained for a theoretical circle and for a circular nurbs.

To do so, I compute the distance in a direction from a random inner point to the shape. The goal is to find the intersection point of the circle with the half-line determined by the point and the direction.

Almost every time, the results agree within 1.0E-13.

But when the intersection point comes next to the loop point of the nurbs, being on the side of the lasts knot vector values, I observe an increase of the error. It seams that it is not observed if being on the side of the starting values of the knot vector.

To be more precise :

For the circular nurbs, the 8 knot vector values are 0, 0, 1/3, 1/3, 2/3, 2/3, 1, 1

When my algorithm works with parametric coordinate values next to 1, I observe an error which seams too high.

Maybe the first question to ask is : Is it possible to evaluate the nurbs curve on parametric coordinate = 1.0 ?