Hi Steve, I'm glad the STEP/IGES/Polygon/NURBS explanation helped!

Please let me know if you need more information or if anything was not clear.

Yes, I think that the really major difference to be aware of is between formats that hold Polygon data and ones that contain NURBS data - that is actually a much larger fundamental difference in the way that the object data is structured.


> I can see now that a cube for example would only truly be
> "solid" if its data referenced every point on its surfaces AND
> also every point within the body of the cube!!

From a purely mathematical standpoint, any method that partitions space into different regions with an "inside" and and "outside" portion is a solid.

A lot of people seem to get the feeling that a solid defined by a connected skin of surfaces is not a "real" solid, but mathematically it is just as real as any other method.

In older systems there used to be a different method used called "Constructive Solid Geometry", or CSG - where solids were defined by a kind of tree structure that combined basic elements like spheres, boxes, and cylinders. That method is not very good for objects that have more sculptured surfaces that are not one of those simple primitive shapes. So it has been a while now that nearly all solid modeling systems use the "boundary representation" method instead which focuses on that connected skin of surfaces. It is a lot more flexible.

Anyway, that is probably more detail than necessary - just to sum it up - MoI uses the same method of representing a solid as those "solid modeling" systems, so a solid that you create in MoI can be exported as a solid to Alibre or SolidWorks (if you use one of those NURBS-based formats). MoI just does not force you to only work with solids, you can work with surfaces as well.

- Michael