digital globes

[RichD]

A new invention, the digital globe:

http://www.nytimes.com/2013/01/08/science/digital-globes-a-new-way-to-view-the-world.html

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?

 

[Roberto Waltman]

A new invention, the digital globe:
http://www.nytimes.com/2013/01/08/science/digital-globes-a-new-way-to-view-the-world.html
... But how does this work, a display on a closed
surface? Anybody have any comments on the design or manufacture?

See the first Youtube video in that page:

"Is simply four projectors around a spherical projection screen"
(22 seconds into the video)

 

[RichD]

The article tells you: "externally or internally projected."
The NOAA setup is externally projected onto the sphere.
http://www.sos.noaa.gov/Getting_SOS/index.html

The article is saying the internal projection system is cheaper but
has the problem of the base blocking projection in that direction.

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.

 

[Martin Brown]

A new invention, the digital globe:

http://www.nytimes.com/2013/01/08/science/digital-globes-a-new-way-to-view-the-world.html

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?

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.

 

[Jasen Betts]

I wonder, how does one build an internal projector,
for display onto a 3-D sphere?

build it in the pedestal put optics in the sphere (mirrors, lenses)

 

[Tim Williams]

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?

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

 

[Martin Brown]

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...

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.

 

[halong]

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.

Interesting ...