parametric or nurbs spline????

[biss03]

Can someone give an explanation of the difference and opinions of which one is better to use( in simple mans terms if possible, I've read the online help but am having trouble understanding it). I don't use them very often for my applications, but when I do, I like to know what I am choosing from. Typical IGES files translated in from PRO-E are parametric.

Thanks in advance!!

josh

[Simtech]

Parametric: curve will pass by the control points.

Nurbs: Non-Uniform Rational B-Spline, curve will be interpolating "weight" of each control point.

Try creating a Parametric and Nurbs spline and modifying the Node points (parametric) or the control points (nurbs). You will see the difference.

You can convert a parametric spline to a nurbs spline with the command Xform to Nurbs.

Luc

[Mariana Lendel In-House Solutions]

Parametric splines require more memory in the database. Mastercam defaults are for NURBS.

[gstephens]

As far as machining, there is no difference. The only time you may have an issue is when convertibg to IGES (or something else) for some other software that doesn't support one or the other.

In short...don't worry about it if you are not doing the initial design work (you are working from someone else's file and/or print).

[Charles Davis]

Parametric can be easier to manipulate precisly IF you need to move the node points (the points the spline passes through).

NURBS are manipulated by moving the control points, which aren't on the spline, but at the vertex of the control tetrahedron.

This means you can't really manipulate a nurbs with the same precision that you can a Parametric (except for the first and last point of the nurb). However, you can manipulate the NURBS nicely for artsy work (that is, muscle the nurb around until it looks right).

In practice, if you move a control or node point, it normally IS the first or last in the spline.

So, all in all, nurbs are better. If you need to manipulate node points, or if you're having problems (like the spline goes wild when you try to manipulate it), use Parametric.

[Tomarik]

Thanks for the explanation of NURBS. I was thinking about redrawing my part with arc segments instead of NURBS. Because it wasn't able to find a path between entities. Then I was having trouble chaining together a line segments with lot's of arcs and "cannot join entities" message appeared when I attempted to. Switching my paths from partial to chained and it allowed me to create the roughing path without joining entities.

[Allan]

14.5 year old topic still relevant and brought to the first page  

[Tomarik]

14.5 year old topic still relevant and brought to the first page

I was pretty impressed as well that it actually moved the topic to first page. Hopefully the topic helps someone else, or gets some more feedback about the topic.