Ooops, I meant to write "If you have fiddled with the tangent handles..."
gray From: softimage-boun...@listproc.autodesk.com [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Grahame Fuller Sent: Tuesday, June 18, 2013 05:05 PM To: softimage@listproc.autodesk.com Subject: RE: bezier -> nurbs Mathematically, Bezier curves are a special case of NURBS curves, although internally some applications might represent them differently. However in Softimage, Bezier curves are simply cubic NURBS curves where every knot has multiplicity 3. The Tweak Curve tool recognizes this case and automatically keeps the tangent handles aligned by default. If you simply draw a Bezier curve and don't fiddle with the tangent handles, then you can trace it as a NURBS with fewer control points using Create > Curve > Draw Cubic by Knot Points and snapping to the knots. If you have fiddled with the knots on the original Bezier, you then need to select all the knots on the NURBS, choose Modify > Curve > Set Knots Multiplicity, set the slider to 3, and finally snap the control points to the originals. Congratulations! You've just duplicated the original Bezier the hard way, which was actually a NURBS in disguise all along anyway. On the other hand if you wanted to know whether it was possible to trace an arbitrary Bezier (where the handles might be uneven/unaligned) using a NURBS with knots of multiplicity 1, then the answer is "no", unless you resample very densely and even then it can only ever be an approximation. gray From: softimage-boun...@listproc.autodesk.com<mailto:softimage-boun...@listproc.autodesk.com> [mailto:softimage-boun...@listproc.autodesk.com] On Behalf Of Ponthieux, Joseph G. (LARC-E1A)[LITES] Sent: Tuesday, June 18, 2013 04:08 PM To: softimage@listproc.autodesk.com<mailto:softimage@listproc.autodesk.com> Subject: bezier -> nurbs 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.
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