Thanks for all your comments. Please find my replies below.

Stephen <mca### [at] aolcom> wrote:
> That is nice. I've not seen that one before.
> :-D

It's indeed far less common than the impossible triangle for example. However,
this illusion is not the first of its kind. See for example
http://im-possible.info/english/art/computer/ausbourne.html or
http://impossible-world.blogspot.nl/2014/03/impossible-cog-wheels.html. The
drawings on the latter page actually inspired this one.

Jim Henderson <nos### [at] nospamcom> wrote:
> Very nice, and a wonderful variation of the triangle (wasn't that Escher?) image.

Thanks. Escher indeed created drawings based on the impossible triangle,


> Now I want to know how it was done. ;)

The basic part of this illusion is quite straightforward to achieve. Two halfs
of the gear, oriented at right angles and placed such that they appear to line
up.

The devil is in the detail though. Given that the surface is reflective (and
also has a subtle normal) a few more tricks are needed to avoid discontinuities.
It's rendered in one go though, and did not require any post-processing.

"jhu" <nomail@nomail> wrote:
> That's unpossible!

Well, apparently not. Ray-tracers don't lie... ;-)

"s.day" <s.d### [at] uelacuk> wrote:
> Very good, I understand how someone can draw something like this but to model it
> in POV... I have no idea how that could be done.

Thanks. My above reply to Jim gives some insight on how to start. One of the
advantages of ray-tracing is that you have quite powerful tools at your
disposal: perfectly accurate object placement,  perfect mirrors, perfect copies
of objects, programmatic textures, etc. Those all really help when rendering
impossible objects.

Le_Forgeron <lef### [at] freefr> wrote:
> Actually, wonderful on a black T-shirt, need a white background for
> printed logo, but not sure it remains as lovely.

Might make a nice t-shirt indeed. The black background really helps to make the
object stand out, so best to leave that unchanged.

> It remind me of Escher, but of different kind.
>
> >
http://www.4-construction.com/fr/magazine/images/formes-geometriques-dans-les-peintures-de-mc-escher_7539/12345/

Yes, it's quite similar to the ribbons in Escher's "Cube with magic ribbons"
drawing. That one, however, is more advanced with bumps slowly morphing into
dents. Maybe I should give that a go as well sometime.

> The gear could be the next General Motors' or any steel/mechanic-related
> company.

It's a question though whether it then represents excellence, or shoddy
craftsmenship ;-)

Thomas de Groot <tho### [at] degrootorg> wrote:
> You truly are a 3D Escherian. Very well done indeed. And beautiful too.

Thanks. This is indeed becoming my ray-tracing specialty. The only thing I can
do reasonably well. Ah well, better that than doing many things poorly I
guess...

Cheers,
Erwin

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