Is it a solid?

[davidcockey]

Question for general discussion, not for any particular reason.

Is the blue surface a solid in Rhino? It is a closed polysurface with no naked edges. The blue object was created by moving the solid points of the green solid.
IsItASurfaceDC01.3dm (97.2 KB)

polysurface

ID: 4ad66314-d860-40c4-aa1b-653c2025f158 (7212)
Object name: (not named)
Layer name: Polysurface
Render Material:
source = from layer
index = -1

Geometry:
Valid polysurface.
closed solid polysurface with 6 surfaces.
Edge Tally:
12 manifold edges
Edge Tolerances: all 0.00
Vertex Tolerances: all 0.00
Render mesh: 6 fast meshes 68 vertices 68 polygons
Analysis mesh: none present
Geometry UserData:
UserData ID: 2544A64E-220D-4d65-B8D4-611BB57B46C7
Plug-in: Rhino
description: RhinoCommon UserDictionary
saved in file: no
copy count: 1

[pascal (Pascal Golay)]

Hi David - I guess (guess) Rhino does not really have a concept of solid more defined that closed and valid with no non-manifolds… does that thing do anything with Boolean operations or does it fail?

-Pascal

[RIL (Rolf)]

@pascal

Rhino does not really have a concept of solid more defined that closed and valid with no non-manifolds

Is this a “quantum solid” with surfaces having two mutually exclusive states at the same time: A watertight volume of closed(?) surfaces where some of them have two normals pointing “outwards”.

That’s deep. Perhaps only möbius strips looks more weird.

// Rolf

[davidcockey]

@pascal

Hi David - I guess (guess) Rhino does not really have a concept of solid more defined that closed and valid with no non-manifolds… does that thing do anything with Boolean operations or does it fail?

It meets those requirements. I have not tried any Boolean operations with it. Volume returns a value of effectively zero.

@RIL

Is this a “quantum solid” with surfaces having two mutually exclusive states at the same time: A watertight volume of closed (?) surfaces where some of them have two normals pointing “outwards”.

That’s deep. Perhaps only möbius strips looks more weird.

Very simple to create though. Start with a block, then swap pairs of Solid Points at one end.

Mobius strips are easier for me to understand.

[RIL (Rolf)]

@davidcockey

Very simple to create though. Start with a block, then swap pairs of Solid Points at one end.

Yes, I got that. Shrewd.

Simple to create, yes, but in general, problems are the easiest to create. Solving problems is often a tad bit harder

@davidcockey

It meets those requirements.

I though that “solid” in Rhino required that all surface normals points outwards. Perhap I got that part wrong.

// Rolf

[jeremy5 (Jeremy)]

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…

[HaLo]

@RIL

I though that “solid” in Rhino required that all surface normals points outwards. Perhap I got that part wrong.

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.

[nathanletwory (Nathan 'jesterKing' Letwory)]

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.

[davidcockey]

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)

polysurface

ID: 997444d3-23e2-43c4-ae1d-8a599853672f (1291)
Object name: (not named)
Layer name: Layer 01
Render Material:
source = from layer
index = -1

Geometry:
Valid polysurface.
closed solid polysurface with 6 surfaces.
Edge Tally:
12 manifold edges
Edge Tolerances: all 0.00
Vertex Tolerances: all 0.00
Render mesh: 6 fast meshes 113 vertices 134 polygons
Analysis mesh: none present
Geometry UserData:
UserData ID: 2544A64E-220D-4d65-B8D4-611BB57B46C7
Plug-in: Rhino
description: RhinoCommon UserDictionary
saved in file: no
copy count: 1

[davidcockey]

@RIL

I though that “solid” in Rhino required that all surface normals points outwards. Perhap I got that part wrong.

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.

@HaLo

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.

The objects in may example would qualify as solid but “weird” by that criteria.

[davidcockey]

One of the twisted surfaces. Note the different directions for the surface normals of what appears to be a planar surface.