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digital globes

Discussion in 'Electronic Design' started by RichD, Jan 12, 2013.

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  1. RichD

    RichD Guest

  2. RichD

    RichD Guest

    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.
     
  3. Martin Brown

    Martin Brown Guest

    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.
     
  4. Jasen Betts

    Jasen Betts Guest

    build it in the pedestal put optics in the sphere (mirrors, lenses)
     
  5. Tim Williams

    Tim Williams Guest

    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
     
  6. Martin Brown

    Martin Brown Guest

    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.
     
  7. halong

    halong Guest

    Interesting ...

     
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