U & V

[Cloud Hidden]

What's the best definition of U and V on nurbs? I see references to them in the documentation, but don't know what determines which direction is which.

[Biplab]

u and v are the parametric directions. Imagine you have a rectangular surface. The parameters at the bottom left may be [u = 0, v = 0] and parameters at the top right may be [u = 1, v = 1].

You can also imagine a tubular surface and the imagine the length of the tube is in the u parametric direction. One might then say that the surface is closed in v (i.e. in v parametric direction]. In VW, only places you see these are the OIP coordinate changes. Also Reverse Normal in OIP reverses the u direction of the surface.

[Bart Rammeloo]

Hello Cloudhidden,

In the last issue of 3DWorld magazine (number 42), you will find a very good (and short) introduction to NURBS terminology. If they sell it in your neighbourhood, I suggest you get a copy

Cheers,

BaRa

[RickBern]

Cloud

Imagine you have a nurbs surface which is an American flag. There is a rectangular surface to this with "u" defined as the direction that runs along the short end of the stripes and "v" defined as the direction which runs along the legnth of the stripes(I'm leaving the stars for later).

No matter how much you deform the surface (the flag waves in the wind) you can still plot a point along the surface as so far in the "u" and so far in the "v".

As was pointed out above a cylinder could be defined as being closed in "u" in which case the long end of the stripes would touch the star field or closed in "v" in which case the short end of the stripes touch the star field.

Hope this helps

Rick