How does this illuminated Beijing advertising technology work?

May 15, 2012 8:35 AM

How does this advertising wizardry in the Beijing subway work?

In Beijing, while a subway train is in a tunnel, illuminated ads often appear, in what looks like a long row of identical projections. The train is moving. Each projection/frame shows a constant, sometimes moving, picture. The entire picture sequence is only approximately synchronized with the forward rate of the train. Then they abruptly disappear. The only people I have asked about it shrug, as they see no interest in the ads. To me it is technological wizardry of the highest order. I can't imagine what the technology is that allows it. Multiple projectors on rails overhead moving back and forward sound highly implausible.

Anyone know if I am missing the screamingly obvious here, or better yet, know the wizardry involved?

posted by stonepharisee to technology (10 answers total)

It sounds like what you're describing is effectively a Zoetrope:

http://en.wikipedia.org/wiki/Zoetrope

There was one of those on the Boston MBTA a few years ago between Kendall Square and Central Square. It's actually about as low-tech as you can get!
posted by scolbath at 8:37 AM on May 15, 2012 [4 favorites]

Wow! I wish I had actually READ the wiki link - looks like the Zoetrope was invented in China! Neat.
posted by scolbath at 8:38 AM on May 15, 2012

Sounds like a subway zeotrope.
posted by rongorongo at 8:39 AM on May 15, 2012

They have this in the BART tunnel between Oakland and San Francisco. It's just a series of regular posters, all slightly different, with lights trained on them, and the "animation" is the result of the train's movement. Works just like a zoetrope -- pretty low-tech, actually.
posted by theodolite at 8:39 AM on May 15, 2012

Yup, used to be on the Red Line. They describe the tech here.
"First, nearly 200 boxes are installed along a tunnel wall, each box with a picture.
When a motion detector senses an approaching train, it sends out a
command that sequentially illuminates each box for a split second. To
someone looking out a train window, the effect is similar to watching
a mini movie."

Here's a poor Youtube video of the effect.
posted by FreezBoy at 8:40 AM on May 15, 2012

Oh how I love AskMeFi. Thank you all very much. That was quick and succinct. I should have thought of the zoetrope, but it just looked so high tech, and what with this being Beijing and all.

Solved, and grateful.
posted by stonepharisee at 8:44 AM on May 15, 2012

They also have them on the tram that goes back and forth between international arrivals/departures and the main terminal in Zurich, although they also add subdued yodeling and cow bells.
posted by GenjiandProust at 8:48 AM on May 15, 2012

I think there is still one at North Station in Boston--not just on the Red Line, but, I guess, the Green Line, too? (It's actually not very good.)
posted by Admiral Haddock at 8:49 AM on May 15, 2012

DC has them, too. When I first saw one I had a bit of a fit.
posted by Chutzler at 8:57 AM on May 15, 2012

Previously.
posted by Mitheral at 1:48 PM on May 15, 2012