[and in another post]
>Then we have to modify the scene as the viewer moves, so as to retain
>the illusion. Maintaining the illusion for multiple viewers would be
>a real challenge. Essentially, you'd have to have everyone view a
>"4D" world: that's 3D + extra processing.
I do like your idea of a 4D world--where you process to get "impossible"
perspective shifts as you move through the world. I think that could probably
get you the famous Escher work with the different-perspective staircases
(please excuse my ignorance of the title).
OTOH, there are some 2D perspective issues that inherently make no sense
from other perspectives: take constellations, for example. A collection
of stars may look like the Big Dipper from Earth, but if you move very far
around the galaxy, it looks nothing like that, because the stars are
different distances from you.
Many Escher works rely on analogous effects, like the picture of the hands
drawing the hands. If you had a true 3D, with a flat plane drawing visibly
shifting into a 3D rendering, it would be a very different effect, because
the flat drawing would only look like 3D from certain angles. You could
design it so that the plane of the drawing was always perpendicular to the
viewing angle, but that too, would yield a very different effect.
One last thought: would any of it look right through a stereoscopic display?
I would think that would eliminate any of the necessary ambiguity.
--Andy
andyn@texas.net