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March 7, 2010

New Technology Selection – DSI

There are several core technologies available to build a multi-touch device – Frustrated Total Internal Reflection (FTIR), Diffused Illumination (DI), Laser Light Plane (LLP), and Diffused Surface Illumination (DSI) are among the most popular.

Previously I had intended to build my table based upon LLP technology as this was the most cost effective of the solutions and despite requiring a little extra TLC and setup provided very strong illumination and finger tracking.  However, there are a few downsides to the technology, not the least of which is the chance of blinding yourself (no, really) with a powerful laser that doesn’t emit any visible light.  This means you won’t realize you’re in trouble until it’s probably too late.  The warning “Do not stare into laser with remaining eye” is ever so relevant here.  If you’re careful you have nothing to fear but this is a concern.  Another is that there’s no really good way to do fiducial (object) tracking with LLP.  Some ideas were put forward but most are experimental and there is little software support for such a setup.  Since I wanted to be able to track fiducials this was a negative, but I figured I’d get the table built first and then deal with this shortcoming later on.

Well, as my previous post pointed out, I’m starting a new build and with that new start comes a new technology choice as the basis for the build – DSI.

DSI utilizes a special acrylic with tiny micro-mirrors embedded throughout the entire surface that cause light injected into the edges of the material to be redirected out of the front and rear faces of the material.  A simple writeup of the technology can be found on the NUI Group Wiki here.  As you would expect a material that exhibits these kinds of properties doesn’t come cheap which is what put it out of reach on my previous build.  With a larger budget this time around DSI has become a viable option.  Given proper infrared illumination DSI provides solid finger tracking without the occlusion concerns of LLP and, most important of all, DSI provides a good basis for fiducial recognition and tracking.

Once I get a bit more design work out of the way I’ll be ordering the materials for this part (the actual surface of the table) – but for now I still have a PC to finish building and a projector to play with.

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