Snow Globe: Part One, Cheap DIY Spherical Projection

By Nirav Patel

Published on August 8, 2011 in Computer Graphics

Since reading Snow Crash, I’ve been drawn to the idea of having my own personal Earth. Because I’m stuck in reality and the virtual version of it is always 5 years away, I’m building a physical artifact that approximates the idea: an interactive spherical display. This is of course something that exists and can likely be found at your local science center. The ones they use are typically 30-100″ in diameter and cost enough that they don’t have prices publicly listed. Snow Globe is my 8″ diameter version that costs around $200 to build if you didn’t buy a Microvision SHOWWX for $600 when they launched like I did.

The basic design here is to shoot a picoprojector through a 180° fisheye lens into a frosted glass globe. The projector is a SHOWWX since I already have one, but it likely works better than any of the non-laser alternatives since you avoid having to deal with keeping the surface of the sphere focused. Microvision also publishes some useful specs, and if you ask nicely, they’ll email you a .STL model of their projector. The lens is an Opteka fisheye designed to be attached to handheld camcorders. It is by far the cheapest 180° lens I could find with a large enough opening to project through. The globe, as in my last dome based project is for use on lighting fixtures. This time I bought one from the local hardware store for $6 instead of taking the one in my bathroom.

I’ve had a lot of fun recently copying keys and people, but my objective in building a 3D printer was to make it easier to do projects like this one. Designing a model in OpenSCAD, printing it, tweaking it, and repeating as necessary is much simpler than any other fabrication technique I’m capable of. In this case, I printed a mount that attaches the lens to the correct spot in front of the projector at a 14.5° angle to center the projected image. I also printed brackets to attach the globe to the lens/projector mount. The whole thing is sitting on a GorillaPod until I get around to building something more permanent.

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http://eclecti.cc/computergraphics/snow-globe-part-one-cheap-diy-spherical-projection

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