I’m with Rolf - it’s open and closed at the same time. I can’t see any practical use for it and if you create its analog while modelling (e.g. a self-intersecting surface) you often find it difficult to clean up. So I guess it would be nice if Rhino could identify it as an invalid object.
And while we’re on the subject @pascal : a request for a Rhino function to split self-intersecting surfaces on the intersection line…
Solid only means no naked or non-manifold edges. Boundary surfaces are oriented to let the normals face outwards. Unless something weird happens, all normals will face outward as a result, not a requirement.
Still this is a weird object that I wouldn’t necessarily call valid, since backfaces show. With realworld objects you don’t see ‘backfaces’, since stuff - solids - always have thickness. You don’t ever see any backface (transparent materials notwithstanding)
For fun extract its render mesh and turn on visualisation of back faces… That and already the original one show those.
Another one. The top and bottom control points on one end have also been swapped. The “hourglass” shape surfaces have been twisted so that the surface normal is swaps sides in the middle…For this one Volume returns 188127.107 (+/- 0.0001) cubic inches. IsItASurfaceDC02.3dm (127.4 KB)
What does “all surface normals” mean in this context? The normals of all surfaces? Or the surface normals everywhere? The latter would be difficult to completely verify. A small corner might be twisted.
The objects in may example would qualify as solid but “weird” by that criteria.