Hello .Thanks for your replies.

Basically ,Iâm following a research paper and trying to understand the way they have parametrized the stent center line. The image that I had posted is the one from that particular literature. In short ,they have fixed the control points,the knot vector, and the degree and only used the weights of the three control points ( the other part being the reflection of the first part ) as decision variables,for the design optimization problem in hand .The below is the para from the said literature:

âThe centerline of a single stent segment is represented

as a NURBS curve. A control polygon with eight nodes is

developed from the stent dimensions detailed above (Fig.).

Further exploitation of the anti-symmetry of an individual

stent segment means that control points 4â7 may be generated

by reflecting nodes 3â0 through the central reflection

point. Furthermore, the weights associated with the control

nodes 0â4 are numerically equal to weights 7â4, thereby

reducing the number of weights to be specified for a given

curve to four.â

Now, it seems like the curve does pass through the mid-point (229,458) .So,if we first draw the lower half n reflect it than we will have to make (229,458) as an end point(i.e control point)