NURBS & Conic Sections

[Stuart Clark <srclark@xxxxxxxxxxxxxx>]

I know it should be easy to draw circles using Bezier curves in Open 
Inventor. I have looked at some literature and it says for example that 
a quadratic rational bezier curve can represent a circle - the middle 
weighting should be cos(theta) where 2 * theta is the angular extension 
of the arc. Yet I seem to get only parabolas. The closest one looking 
like a circle has a middle point weighting of one. ??? I am lost.

Any help would be appreciated. Here are the values I am using:

float pts[3][4] = {
               {1.0,0.0,1.0,1.0},
               {1.0,1.0,1.0,0.707},
               {0.0,1.0,1.0,1.0}};

float knots [6] = {0,0,0,1,1,1};

Thanks in advance,

Stuart