Help: Cannot hide some lines in display

I’ve got a technical display view (based on the pen display mode). There are some lines between some surfaces that I’m unable to get to hide. I have show creases, show seams, show intersections, show hidden lines, and show curves all disabled, but these are still there. The geometry came from a solid CAD model, so I’m pretty sure that it’s curvature continuous across these edges. I have verified that the whole thing is a watertight polysurface.

Any suggestions for how to get rid of the lines shown by the arrows in the image? I’m out of ideas.

Those are Isocurves.
You can suppress the display in the isocurves in Options > View > Display Modes > [your display mode name] > Visibility section. Uncheck showing isocurves.

Interesting. I don’t have that specific option. Here is a snip of my settings in this section.

I doubt that those are isocurves. They look like edges (seams). Since you want to show edges, you will also see these.

@wim Is there any way to get rid of them? I tried ‘merge edges’, but that didn’t work.

The default Pen mode does not display isocurves. That must be an Edge or a Seam. Try turning off Edges

I can confirm that turning off edges hides them, but it also hides almost everything else I’m interested in seeing. Is there a way to merge or replace several surfaces with a new, single surface? I know how to do this with curves using Rebuild on a polycurve. Does this same thing work on surfaces?

You may be able to Extract that trimmed surface and use SrfSeam to move the seam around to the other side where it doesn’t show, then Join it back into the polysurface.

Models imported from other CAD systems will most often have cylindrical and revolved surfaces split in two half where Rhino can deal with one single surface. There is no automated way to make two such surfaces back into one (it is on the wish list though) so you will have to recreate those surfaces manually. Then make sure that the single seam is turned away from the camera.

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Thank you all. I think I’m understanding this better now and have a path forward.