If the desired curve is a B-spline or a NURBS curve, you have three
choices: **With Uniform Knots**,
**With Clamped Knots**, and
**With Closed Knots**. This indicates
the different way of arrange the knots.

If you choose **With Uniform Knots**, the
curve will be tangent to the first and the last line segments of the control
polygon (the above left figure). Please note that 0 (the button knot) and
1 (the top knot) are multiple knots. In face, if the curve is of degree
** p**, the multiplicity of 0 and 1 should be

If you choose **With Uniform Knots**,
the curve will not be tangent to the control polygon and every knot is
a simple knot. This is shown in the above middle figure.

Finally, if you choose **With Closed Knots**,
the curve becomes a closed loop and some knots are shown with a different
color. Knots marked with blue triangles are normal knots, while
those non-blue triangles marked special knots that cannot be manipulated.

**You can change the curve to another form at any
time. Just select
Curve, followed by
Show Curve Segment, followed by the
desired form.**