Paper card model from MoI 3D model?

 From:  Michael Gibson
2392.8 In reply to 2392.7 
Hi Mark,

> Michael, is MoI able to constrain a surface so that
> it is forced to be "developable"?

Not in a fully general manner - for example there is not any kind of "force to be developable" checkbox that you can set.

However, I suppose it would be possible to enforce this yourself if you stick to only a few specific tools and operations that create developable surfaces.

Extrusions should be ok, also probably a sweep of a line segment along a path may do that. You may also be able to edit the points of an extruded surface (see this FAQ question for how to turn on points for some objects) and still maintain developability. You may need to use some kind of surface analysis tool to examine the Gaussian curvature of the surfaces you are working on to make sure they are developable.

In general though that is a pretty specialized requirement, MoI is not focused on that particular area of specialized modeling so if you need to create only developable surfaces you will probably be better off using a tool that is more specifically designed with that in mind - MoI's toolset is focused on much more general shapes.

If you convert to polygons though, that simplifies things a lot and you would be a lot more free to use any tools that you want in MoI and then send the polygonized output to one of those programs (Pepakura or Lamina Design).

> Then, if I'm understanding what Alcides has said about Rhino,
> I unroll my surfaces (or perphaps a selection of surfaces?)
> rather than unfolding entire polygon meshes?

Yes - if you wanted to work in this way you could use Rhino's "UnrollSrf" command which is able to calculate a 2D pattern from a developable surface (and only from developable surfaces). That is an alternate possible way to approach the problem rather than unfolding polygon mesh data. But in general you should probably expect to spend quite a lot of time learning many details about developable surfaces if you want to go this route, it tends to be more used by people who are going to construct their final object out of sheet metal.

- Michael