Baseball cap head-up display

For a while now I’ve been interested in augmented reality. Working in the field of geospatial science, I’m always looking for better ways to present location-based information, and augmented reality shows a lot of potential. Plus I’m a big fan of science fiction, and AR interfaces have featured in some of my favourite movies – The Terminator (1984) and Robocop (1987) – as well as some of my favourite books – Neuromancer (1984) and Virtual Light (1993).

But although the idea has been a part of popular culture for nearly three decades, the reality has been disappointing. Head-up displays have long been used by military pilots, and are starting to be deployed in luxury cars, but personal units have been gimmicks at best. There have been augmented reality motorcycle helmets and ski goggles, and Google is rumoured to be releasing Google Glasses by the end of the year, but none of them provide a full field-of-view display. This limits their ability to provide fully immersive graphics or even to play movies.

So I decided to build my own. How hard could it be? Not very, it turns out.

I put one together using a smartphone (an HTC Desire Z), a baseball cap, a couple of fresnel lenses, a plastic mirror, some mirrored film from an iPhone screen protector, and assorted office supplies. The smartphone is held in place with a rubber band, and whatever appears on the screen is displayed in the wearer’s field of view. The fresnel lenses are there to push the screen’s perceived distance out to about 50cm, otherwise you’d get serious eye strain.

It works pretty well. Lining up the reflective screens is fiddly, so future designs should lock them in place. They also don’t work too well in direct sunlight, since the mirrored film isn’t very reflective, so the reflected light from the screen is pretty dim. Ideally you’d want some sort of mirror that automatically adjusts to the ambient light, and you’d want the smartphone screen to dim at night, but these work fairly well indoors.

The image quality from fresnel lenses is mediocre at the best of times, but I was forced to use a pair of these in series to get the focal length short enough. As you’d expect, that creates a fair bit of distortion at the periphery, especially since the mounting isn’t very rigid. It would be better to use a single, rigid lens, with just the right focal length – preferably a bit shorter than my current setup, since the 50cm screen distance is a bit too close to be comfortable. I suspect that the best solution would be to do away the fresnel lenses altogether and use curved mirror-tinted surfaces to display the image, but that’s beyond my design and manufacturing ability.

My HTC is fairly heavy with its slide-out keyboard, and with all that weight on the end of the bill you need to put the cap on nice and tight to keep it in place. Something a bit lighter, like an iPhone, would probably be more comfortable.

But it works as a proof-of-concept. It’s pretty cool to run Wikitude with some duct tape over the camera lens, and see all the points of interest rotate around as you turn your head. Now all it needs is some custom software so I can see where I’m going while I read my e-mail.

Taking pictures of an inside view of the display was tricky. In the end, I turned the cap upside-down, stuffed a t-shirt in it, and rested a manual-focus camera on top. The resulting pictures were taken through an upside-down display, but you get the idea.

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