The Solution

On four shows now, I have continuously found the best tool to fix this issue not to be a commercial, several thousand dollar worth, “does everything” 3D application like Maya, XSI or Houdini.

But rather a small, free, open source, specialized modeling application called Wings 3D.

Wings calls itself a “subdivision surface modeler”. This is arguable in the same way I touched on at the start of this article: namely that the subdivison modeling tool sets of most 3D applications don’t actually edit the subdivision (limit) surface at all, but rather the control polyhedron (or cage). I shall write an essay about this marketing-department born misconception another time. What matters in the context at hand is that Wings actually guarantess the surface to stay manifold regardless of what crazy editing operation the user performs.

How does this help us with the problem of models created in other applications? Simple: Wings ‘fixes’ any model on import to be manifold automagically. Non-manifold parts of the geometry get either thrown away or marked as ‘holes’, i.e. faces that are invisible.

Thus, the only step one has to take to fix a model with Wings is commonly importing and straight exporting it again. ‘Hole’ geometry gets omitted from export. The least common demoninator for may applications is the Wavefront Object format.

Wings’ Supported Formats

Wings supports importing:

• 3D Studio (.3ds)
• Lightwave (.lwo),
• Nendo (.ndo)
• Modo (.lwx)
• Sterelotigraphy (.stl)
• Wavefront Object (.obj)

Data can be exported as:

• 3D Studio (.3ds)
• DirectX (.x)
• Lightwave (.lwo),
• Nendo (.ndo)
• Modo (.lwx)
• RendeMan (.rib)
• Renderware (.rwx)
• Sterelotigraphy (.stl)
• VRML 2.0 (.wrl)
• Wavefront Object (.obj)

I can only suggest introducing this as a quality assurance step to anyone working with 3D models that are later to be rendered as subdivison surfaces.