Offset fail

Grinding teeth here… I might be going about this the wrong way but I’ve tried all options I can think of.

I have a surface I want to offset. This is the 2nd revision made with networksrf (half > mirrored > rebuilt), 1st revision was lofted but essentially the same problem remains in both versions.
The offset surface edges go wonky and turn inside out regardless of direction or if solid or not. I’ve merged edges, tried making the surface uniform. It has something to do with the edge seam I think but I just can’t figure it out.

Any ideas? Should I build the original surface some other way, and if so, how?
rev2_copy.3dm (164.9 KB)

Hi Stefan- the four corners of this surface all have parallel U and V:

This is allowed but not a really good way to do things- in particular the surface normal direction is not defined when U and V are parallel and offsetting does not know what to do - NURBS prefer to be in a grid arrangement and the grid falls apart here. Better to make hard corners and trim the rounds in this case, or make a border all around a trimmed inner surface.

Here is a version that has the corner points re-arranged just a little and the corners trimmed off - that should offset.

rev2_copy_PG.3dm (158.7 KB)


Hi Pascal and thanks for your reply!

I see the UV issue now thanks!
My guess is you Duplicated border > dragged corner points outward > trimmed from top view using the duplicated border curve?
For future reference, what’s the best way to build this kind of surface from scratch? Because in many cases it’s important to accurately define borders and contours using curves before committing it to a surface.


Hi Stefan - one way is to trim back the surface and make a transition to the border curve- either ‘locally’ per corner, or all the way around as in my example here.

rev2_copy_PG_2.3dm (206.6 KB)


Hi Stefan, just for the heck of it, I monkeyed a little with the surface points to try to clean up Zebra and Emap, just a little- I’ll post my file in case it is of use…

rev2_copy_PG_3.3dm (245.3 KB)


Appreciate it @pascal! Thanks!

Your model proved a nice surface but it caused some issues down the workflow.
I’ve managed now to make a clean rectangular (top projection) surface from scratch using networksrf. It has a nice simple UV and zebra looks delish.
My question is in regards to trimming the surface corners. As with any complex surface, trimming the surface from one view will most likely cause an uneven edge with dips and bumps in another view. It’s to do with how the trim curve projects in relation to the views.
Is there a way to edit the surface edge(s) without exceedingly affecting the enclosed surface UV to adjust silhouettes and vice versa, edit the surface while maintaining the edge(s)?

To clarify, attached a mock up copy.
I crv2viewed my side silhouette and the trim curve on cplane. Now I would just like to match the surface edge to the new curve. Any help highly appreciated.

Best regards,

Untitled copy.3dm (177.7 KB)

Hi Stefan - the surface is a little too dense to easily modify - I would make it simpler and use Project with History to help modify the surface.

  • Make a simple surface- I did half at a time here.

  • Project the plan curve, with History onto the surface. (Blue curve)

  • carefully manipulate the surface points until the blue curve approaches the curve you like.

  • I also pulled some curves out of your surface and projected them with History onto the surface (Cyan curves) so that I could see how the shape was in the middle of the surface, compared to the original.

It 's possible you may need one more row of points to get the shape right, but I don’t think more than that.

Untitled copy_PG.3dm (195.9 KB)