How to align Controls Points with Surface


Dear All

Happy New Year!
control points.pdf (48.2 KB)
control points.pdf (48.2 KB)

I just wonder is there a way to align the Control Points of a trimmed surface to a particular edge direction? ie turning the control points to face a certain direction?

I have attached a screen shot of a trimmed surface (shrinked) but the control points are following the original untriimed surface orientation, What I want to achieve is to orient the points to align with one of the edge direction of the trimmed surface as shown with the RED DOTS.

Is this possible at all? Thanks for any help !!

Best regards

(John Brock) #2

The topology of a NURBS surface is a rectangle. Your surface shape must be made with an trim curve to define the boundary because of it’s roundish shape.

I can’t see how it would help, but you could detach the trim curve and delete the underlying surface. The make another deformable rectangular surface that is oriented how you want, then trim it with the curve you saved.

I don’t understand what problem that would solve.

(David Cockey) #3

No simple way to do it.

You will need to build a new surface with the isolines aligned in the desired direction.


Thank you John, my purpose of re-orienting the points is to adjust the end portion of the surface but I need to keep the starting end tangent G1-2 to another surface, since the tangent should happen all the way along the starting end (along the red dots), I don’t think I can achieve this if I do not re-orient the points.

(Pascal Golay) #5

Hi Edmond - can you post the surface and the surrounding ones that come into play for matching tangency etc.?



Hi David, thanks, will have a go at it!


tangency surface.3dm (710.1 KB)

Hi Pascal

Thanks for your reply. Yes, I have included it herewith.
On the left its the original surface being split by the tear-drop shape.

What i need to achieve is to lift the control points up on the right hand side of the surface, I have also left the first 3 sets of points untouched on the left hand end as shown on the right-hand model.

However, the result is obviously not a tangent transition.
I have tried to split the surface by its isocurves which works well as the resulting points will follow the surface direction but what I need its the tear-drop shape, thats why I need to re-orient the control points (a bit like rotating the cage to align to a certain direction).

Thanks for your attention!

(Pascal Golay) #8

Hi Edmond - I am not sure I can picture what the end result should look like exactly, but a possible solution here is to cut your surface too small - with a sufficient margin all around to insert a blend surface.
The thing is, with the trim falling as it does (an arbitrary curve) there is no surface point arrangement that could really keep the surface tangent to the larger surface in any very predictable way.



Hi Pascal

Thanks for your advise, that’s what came to into mind eventually as well.

I suppose it would not be mathematically possible to rotate the cage of the control points like that done in the polygons modeling e.g. 3D Max where the cage of FFD can be manipulated due to its fundamental compositional difference.

Thank you so much!
Best regards