Firstly - Full credit for the Openscad program, and my awareness of this, goes to Ed Nisley from his blog over at http://softsolder.com/ (If you are into hacking in the true sense - gadgets, cnc's, electronics, home repairs, just damn interesting 'stuff', then check out his blog! his not selling nunthin' )

Having a moment between 'stuff', I felt like having something novel to fiddle with that was also educational Anyway, over at softsolder I recalled an article ( here - Ed's moved onto a very nicely setup M2 now, so don't hold the thing-o-matic against him ) that provided a nice model that demonstrates the limitations of describing 3D objects in a traditional "plan"/"elevation" sense . This is why its difficult to just 'scan' something - such as a photo - and reliably recreate a 3D model.

Anyway, If you take 3 cylinders and intersect them like the image below:

you end up with a shape that you can view;
as a circle from the top:

plan and side views

But something else entirely when viewed from diagonal;

It will roll like a cylinder on a desk or down a hill, and doesn't feel like a hexagon when rolled in your hand.

Attached is the STL I printed - use .25mm, 25% infill, 2 perimeter, but you can produce your own using the openscad code on Ed's blog. It also uses his filament pin alignment system - use a 1.75mm piece of filament (its 2.9mm in his openscad code) cut to about 10mm to hold the sides together, using some glue to permanently bond it - although the pins in my piece hold it together fine.