Roman Black wrote:
>
> Jinx wrote:
> >
> > > Hi Olin, I once saw a design for a 3D display,
> > > they had a vertical clear plastic panel, rotated
> > > vertically, then projected a scanned laser onto
> > > it from the side...
> >
> > A few years ago I saw an idea (very enthusiastically presented)
> > to create 3D images. Imagine a perspex cylinder about 40cm
> > diameter and about 50cm high. Inside it, central and vertical,
> > was a reflective helix, one complete 360 degree twist, that
> > reflected images projected from the bottom of the cylinder. As
> > the helix turned, the edges of it rose and so the image was
> > scanned onto the perspex. Although it looked good on 2D TV,
> > that's another idea that seems to have risen without trace
>
> I like that idea a lot! :o)
> You need to spin the helix and the laser, with
> one laser axis, (surplus laser printer engine?)
> or rig a 2d laser scanner with a spinning helix.

Unfortunately Texas Instruments has a patent on drawing 3-D images
on a spinning helix. I was royally pissed to discover this in the
late eighties because I'd prototyped it years earlier using a
photocopier lens and a CRT after seeing an article in Byte magazine for
creating a 3-D image using an oscilloscope and a spining mirror.
The byte article even had 8080 code for generating simple vector
graphics.

I didn't have a laser so I just use very bright 9" monitor
to image onto the spinning helix, with the verticle sweep
sychronized with spin so that different pixels mapped to
different heights. With the computer that I used (PDP11/34)
there was no way to do anything -real time-, but it
was an interesting exercise, and looked really good in
a totally dark room. I knew that a laser was the way to go
but couldn't afford anything like that back then.

> What did you think about the spinning panel of
> leds? It might be low-res but could provide a
> simply constructed way of doing this...

As noted earlier, it's been done, and it does work.
I seem to recall seeing the spinning block of LED's mentioned
in Popular Science's 'Science news' column.

> -Roman

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