Bezier and NURBS are different. NURBS have a weight attribute on each knot that allow you to adjust the curve. You cannot create a perfect circle with bezier curve but you can with NURBS curves because of the non-rational attributes (weighting or the Knots).
On Tue, Jun 18, 2013 at 4:39 PM, Daniel Brassard <dbrassar...@gmail.com>wrote: > Oops, reverse. > > From the book > > Multiplicity is a property of knots that refers to the number of control > points associated to a knot. On a cubic curve, a knot can have a > multiplicity of 1, 2, or 3. On a surface, each knot curve has two > multiplicities: one in the U direction and one in V. All knots along a knot > curve must have the same multiplicity in the corresponding direction. > > Knots with a multiplicity greater than 1 are sometimes called *multiknots*. > Multiknots allow for greater control over the trace of the curve through > the knot, at the expense of smoothness. > > - > > A knot with a multiplicity of 1 has C2 continuity (curvature). > - > > A knot with multiplicity 2 has C1 continuity (tangency). > - > > A knot with multiplicity 3 has C0 continuity (position) if the three > control points are not lined up. It is like a Bézier point, with one > control point exactly at the position of the knot on the curve and the > other two control points acting like tangent handles. You can manipulate > these knots on curves in a Bézier-like manner — see Using the Tweak > Curve > Tool<http://download.autodesk.com/global/docs/softimage2013/en_us/userguide/files/curves_DrawingandManipulatingCurves.htm#WS20FD922AA9DF2240AD94FFADCE73807F-002F> > . > > > > On Tue, Jun 18, 2013 at 4:36 PM, Daniel Brassard <dbrassar...@gmail.com>wrote: > >> Raise the knot to multiplicity 3 (similar to bezier) >> >> Lower the knots to 2 (curvature) first and second derivative continuity, >> smoother curve. >> Lower the knots to 1 (tangent) first derivative continuity, tangent >> continuity >> Lower the knots to 0 (linear), sharp turns, no continuity between knots >> >> >> On Tue, Jun 18, 2013 at 4:08 PM, Ponthieux, Joseph G. (LARC-E1A)[LITES] < >> j.ponthi...@nasa.gov> wrote: >> >>> Its been so long since I’ve tried this in Soft I can’t remember…**** >>> >>> ** ** >>> >>> Is there any logic or formula that will allow you to replicate a Bezier >>> Knot curve as a CV curve?**** >>> >>> ** ** >>> >>> I thought all you had to do was make sure the CVs on a Nurbs curve >>> matched the handle points on a Bezier curve and they would align perfectly, >>> but the continuity of the Bezier curves is slightly different than the >>> Nurbs, almost as though the Bezier is a different degree than the Nurbs >>> curve. Is that the case?**** >>> >>> ** ** >>> >>> Second, is it possible to convert a Bezier curve to a Nurbs CV curve and >>> maintain continuity, bias, etc?**** >>> >>> ** ** >>> >>> --**** >>> >>> Joey Ponthieux**** >>> >>> LaRC Information Technology Enhanced Services (LITES)**** >>> >>> Mymic Technical Services**** >>> >>> NASA Langley Research Center**** >>> >>> __________________________________________________**** >>> >>> Opinions stated here-in are strictly those of the author and do not **** >>> >>> represent the opinions of NASA or any other party.**** >>> >>> ** ** >>> >> >> >
