Non manifold geometry not previewing in GH


I am trying to preview some geometry in Grasshopper and I’ve discovered that it doesn’t like non-manifold geometry. The geometry isn’t previewd. Is this a bug?

If it’s not possible to preview non-manifold geometry, is there a way to identify which elements are problematic so that I can explode just those elements?


non (6.2 KB) Non manifold.3dm (2.5 MB)

What does “non-manifold geometry” mean? Something is weird about preview though, I can see that.

As far as I know, non-manifold geometry is geometry that can’t exist in real life. Not sure if this applies here, too

“Non-manifold geometry” in Rhino means a polysurface with three or more surfaces are joined along the same edge, or possibly the edge of a surface is joined to the middle of another surface.

Non-manifold geometry can result in problems, particularly if closed volumes are involved.

ShowEdges command in Rhino with the Non-manifold edges option selected. Set the edge color to a color which will be visible, such as magenta, red or green.

SelNonManifold will select polysurfaces with non-manifold geometry, but it does not show the specific non-manifold edges.

Wireframe mode is helpful when looking for non-manifold edges.

Non-manifold DC2

Non-manifold DC1

Non-manifold I think on its own is considered invalid, but there are additional issues with that shape. Using the Null Item component we can inspect the validity:

Grasshopper will not attempt to draw invalid geometry, as that may result in crashes.