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Creating a solid bounded by wireframe #237

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whitequark opened this issue Apr 16, 2017 · 5 comments
Open

Creating a solid bounded by wireframe #237

whitequark opened this issue Apr 16, 2017 · 5 comments

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@whitequark
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whitequark commented Apr 16, 2017

Right now, there are certain classes of solids that are extremely tedious or completely impossible to define in SolveSpace. These include:

  • platonic solids (except cubes)
  • Archimedean solids
  • stellations
  • frustums
  • certain pyramids

and so on.

Some of these could clearly be done in the spirit of SolveSpace (for example, a frustum group would cover right pyramids and frustums). However, many others aren't. They are needed somewhat rarely, but when they are needed, you are essentially out of luck right now. If you could import STEP, which you will be able to in not-so-near future, then that would not be a show-stopper, but it would still break parameterism completely.

Question is: can we add an escape hatch for this? Allow defining a solid with a set of lines and points; perhaps even drop curves. How hard is it to integrate with our NURBS backend? How hard would it be to define a reasonable UI? Is the operation even well-defined, in general?

cc @Evil-Spirit @jwesthues

@jwesthues
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jwesthues commented Apr 16, 2017

I don't think a useful "shell from wireframe" group is too hard. Take the lines/edges in 3d, and find all the planes defined by some set of adjacent edges. In each plane, find all the closed loops, and those are your faces. Then test that the faces make a watertight, non-self-intersecting shell, choose their normal directions to be consistent (like by choosing one arbitrarily, and then flooding out from its edges), and then make sure the shell isn't inside-out (like by computing its volume, and flipping all the normals if it's negative). Curves get trickier, but I doubt the plane version of this would be more than a few hundred lines of code.

@Evil-Spirit
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Evil-Spirit commented Apr 16, 2017

@whitequark, This is looks like common triangle mesh editing mode like it done e. g. in 3d studio max. We are defining the common 3d entities(segments, circles, arcs) and introduce something like "3d polygon" request which creates planar face from set of looped edges and perserves points to lay in the same plane using solver equations. This is like direct modeling in the context of single group of SolveSpace's history based approach. We can also introduce watertight and solid checks in the same way like it done for checking closed contours.

@whitequark
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whitequark commented Apr 16, 2017

Hm, this is a very interesting idea. We can add a "direct modeling group", where you would use parametric entities, but unlike regular draw-in-3d groups, the group would also include a solid, defined in the way @jwesthues described above. I think this solves all UI concerns I had.

@phkahler
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phkahler commented Jun 5, 2019

Would it be OK to have a checkbox on sketch-in-3d groups that causes a shell to be created from the entities in the group? There would be limitations on what you can create a shell from, but the UI would just be a checkbox. This shouldn't be hard for straight edges and convex objects.

@whitequark
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whitequark commented Jun 11, 2019

The restriction to convex objects seems quite unfortunate. Does it buy us much?

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