Trim Surface With A Curve

Questions
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1

Hi Guys,

I’m trying a trim a parametric surface (made via NURBS Geometry) with a separate curve. Does anybody know how I can go about doing this? I’m confused as to where to start. Would appreciate any help!

Thanks,
Amit

2

When you talking about trimming, I guess you are looking for a similar effect like when using clipping planes?

https://threejs.org/examples/webgl_clipping

If so, I’m afraid there is no easy way to implement this with a custom NURBS surface.

3

Hi Mugen, thats right clipping but with curves. Do you know of a hard way to do it? I’m willing to get it done any way possible

4

No sorry, I’ve never seen something like this done.

5

Do appreciate the suggestions though

6

In both this question and Whats The Best Way to Convert Surface of Points to a Surface?, it seems like you may be looking for a modeling program rather than a rendering library… Creating complex parametric surfaces with code is a more advanced topic and often requires a fair bit of math. In many cases it’s easier to create the shapes you want in a free program like Blender, export them to glTF, and then load that into three.js.

7

Hey Don,

Thanks for taking notice. Basically I am working on a project to read STEP files to three.js. I am able to render almost all surface type except NURBS surfaces. The STEP file defines the NURBS surface but seperately defines edge bounds to the surface. I am trying to find an adequate way to display a NURBS surface that is trimmed according to edge curves/bounds as defined in a STEP file. If you see the graphics of my last response in this thread: How To Make Curved Surfaces, you can better understand what I am trying to say

8

I have no experience with STEP. But maybe you can use a similar procedure on the edge as it is done in triangulation according to E. Hartmann.

I have realized it for implicit surfaces and also explicit forms.

See

Addon for triangulation of implicit surfaces/ forms with holes

https://github.com/hofk/THREEi.js

Triangulation sphere with holes
Triangulation cylinder with holes
Inner Geometry (Triangulation)

9

The geometry manipulation of NURBS geometry is a pretty complex. Don’t think NURBS themselves support clipping. Commonly they’re hosted in a data-structure called Boundary Representations (BReps), which does something like a masking to show clipped surfaces.
Easiest way to make it work online with threejs that I’m aware of might be an experimental McNeel project based on OpenNURBS.