Hi Brian,
> Question 1: Why?
It's a display glitch that can happen with Beziers that have a particular "S" type shape with the start and end tangents going in the same direction. It's unfortunately not easy to fix since the fix involves more thorough tolerance testing of the polyline approximation of the curve, and more testing is not good for performance.
So basically fixing this bug would cause some slow down for drawing all curves. Since it happens rarely and will incur a performance penalty to fix I have not tried to fix it so far.
There's a more detailed explanation here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4101.2
> Question 2: Do you have any tips, or references, to how to convert the Bezier curve into Nurbs?
NURBS are basically a generalization of Beziers, if you have a NURBS curve with only one span in it (meaning the number of NURBS control points = curve degree + 1 like 4 control points for cubic), that NURBS curve will be a Bezier.
So to convert from a Bezier to NURBS it's pretty simple, you just make a NURBS curve that has the same degree as the bezier and has the same control points in it, and just give it a single span unit length knot vector.
> I'm guessing that there is no way for a Moi user to plot a Nurbs equation without delving
> into the .3dm file format and C++ code.
> (I recall seeing some very basic .3dm file C++ code on the Rhino site a while back.)
That's correct, currently all the detailed low level NURBS information like curve degree, control point weights, and knot vector are not set up to be accessed by a script as of yet. But yes if you are writing C++ code you can use the OpenNURBS library to open a 3DM file and get at that information.
- Michael
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