Algorithm behind ConvtoNURBS command (Solid to NURBS)

[ssj5165]

Hi,

I am curious to learn- how does the ConvtoNURBS command generates control points and degree in the u & v directions for any given surface? I would love to know what is the basis of generating the control points and degree in u & v directions that represent that particular geometry?

I also would love to know how is the "maximum deviation" value calculated while rebuilding the NURBS that is generated?

I faced an issue while attempting to enter the default generated value for the degree (the value in parenthesis "( )"), which gave an error that I must select a value that is greater than the existing value. (Note: I made sure the number of control points in that direction was greater than "degree + 1").

Additionally, it would be great if there was a way to extract these control point locations. It is a great tool while learning about NURBS!

Thank you,

Sagar Jalui

[leeminardi]

 A NURBS surface can exactly represent a cylindrical surface so there is no "deviation". The NURBS is degree 2 in the arc direction of the cylinder and degree 1 in the height direction.  An arc of 180° can be represent by 5 CVs but it should be noted that the weights of the CVs are not all 1.

This thread has some good information about the AutoCAD NURBS representations of a cylindrical surface.

Also note that the number of CVs should be greater than the degree (not "degree +1" as you state).  E.g., 4 CVs or more can be used to define a 3rd degree NURBS.