Open surface lines not isocurves


I’m not sure why this surface that I made has funny lines all over it that are not isocurves, so unchecking the show isocurves box in properties does not cut it. I’d like them to go away in order to make a nice shaded drawing.

What are they and how can I get rid of them please?

Kind Regards


rudder_w_lines.3dm (14.3 MB)

It is a polysurface. The lines are the edges of the individual surfaces. Use the What command to find out what an object is.
Valid polysurface.
open polysurface with 2283 surfaces.

How did you create the polysurface?

Hi David,

I think it was a Sweep2 through using a single section and the perimeter rails. But I’ve sinve exported it as an STL and had it machined out, so it may have been corrupted if I was a bit negligent, perhaps?

Do you know what function I could use to merge it into a single open polysurface? I’ve tried, MergeSrf and fitSrf and refit. I could just rebuild it by extracting the curves again, but it’s really annoying not knowing how to fix it or what went wrong!

What did you “extract” the curves from? How did you extract the curves? If the input curves to Sweep2 are polycurves the final surface will be a polysurface.

I didn’t extract, originally. I used a control point Crv if I remember correctly. I mean I could DupEdge to extract a curve or section through if necessary, but I’d like to know what I did wrong and how to fix it rather than re-do it.

The individual surfaces are degree 3 with 6 control points in one direction. In the other direction most surfaces are degree 1 with 2 controp points but one column of surfaces are degree 1 with 3 control points… That rules out the surfaces having been created by MeshToNURB.

The polysurface is consistent with being created using Sweep2 with polycurves.

Where did that control point curve originate? Did you import it from other software.

It’s possible that it came from Autocad. The profile was specified by a naval architect. But as I remember it, I just got the offsets and drew it. It was a Wortmann profile. Sorry I really don’t remember. Would you suggest I just redraw the surface?

Recreating the surface would be the easiest step. If you want a single surface you will need to use curves, not polycurves, as input.

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Hi Giles,

No need to rebuild the rudder then. Simply use a display mode which does not show the surface edges. You can SetObjectDisplayMode to Rendered for individual objects per viewport and show the rest of the geometry in viewport shading mode.

Hi Jess,

I wasn’t aware I could SetObjectDisplayMode, that’s genius. I’ll see whether I can sort it with that. I’d still like to just have it as a single surface if that’s possible!

Well, to get a single surface it needs recreation like David already said. It is not so simple to explain… but maybe the attached is good enough. I would have aligned the profile curves different (more like the ribs in your welded rudder), but that’s a different story…
Rudder_Half_jm.3dm (648.8 KB)

Thanks Jess. I think I must have blanked David’s comment, which I’m sorry for!

I see you’ve used multiple profile curves which has helped them to stay alligned with the top edge. As you say, that is a better alignment and was how I cut the metal rudder sections.