A new invention, the digital globe:
This looks fantastic, as an educational tool, with endless possibilities. But how does this work, a display on a closed surface? Anybody have any comments on the design or manufacture?
-- Rich
The article tells you: "externally or internally projected."
The NOAA setup is externally projected onto the sphere.
The article is saying the internal projection system is cheaper but has the problem of the base blocking projection in that direction.
See the first Youtube video in that page:
-- Roberto Waltman [ Please reply to the group, return address is invalid ]
view-the-world.html
I wonder, how does one build an internal projector, for display onto a 3-D sphere?
Even a set of external projectors seems quite a challenge.
-- Rich
Think Zeiss planetarium with accessories.
-- Sam Conservatives are against Darwinism but for natural selection. Liberals are for Darwinism but totally against any selection.
Seen the large one at the Kensington Science Museum in London. That is a very large ~3m passive sphere illuminated by projectors hidden off stage and high up and by the look of it anamorphic optics and masks to map the images onto the globe with nearly uniform illumination.
It is a glorified slideshow mapped onto multiple synchronised projectors and one spherical projection screen.
Seriously expensive kit at around $50k. Great for museums and the like. My instinct is that it is easier to do a large one than a small one.
Internal projector for a smaller one could be made to work but it strikes me as a very expensive thing for a school to buy (and then have to repair when someone plays football with it). Question is how few internal projection units can you get away with and how expensive are the optics to do the anamorphic mapping for uniform illumination?
OK as another hitech toy for the man who has everything I suppose.
-- Regards, Martin Brown
build it in the pedestal put optics in the sphere (mirrors, lenses)
-- ?? 100% natural
Curious problem: making the optical version of an (near) isotropic radiator.
Is there a theorem that says you can't build one phase-coherent? A true isotropic, no, but we can make the exception that it needs to have a "mushroom stalk" for hookup, and the "mushroom cap" should be as even as possible.
It'd be very difficult, at any rate, to make equal path lengths to the mirrors/lenses to the spherical surface, especially along the peculiar paths needed. Maybe it could be predistorted with filters and holograms, but man...
Tim
-- Deep Friar: a very philosophical monk. Website: http://seventransistorlabs.com
Having thought about it some more I think the easiest solution although not likely to survive in a school environment would be a linear array of RGB LEDs around the edge of a longitudinal disk and spin the whole lot to illuminate the sphere from the inside. Do it well and you might be able to dispense with the fragile outer projection skin.
At one stroke you avoid all the optics and can get even illumination by software adjustable PWM means. A glorifed version of those novelty wands you wave about to show a message suspended in the air.
-- Regards, Martin Brown
Interesting ...
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