a few month ago i collaborated with maddi boyd (kisskiss) on a mixed media art installation titled timebomb. it consisted of an interactive projection which allowed for people to peel back the layers of a graffiti wall. you can read more about it at this earlier post.
the opportunity came to exhibit the installation again and instead of doing the same old, maddi and i decided to push the idea further and take timebomb away from the 2d flat canvas into a 3-dimensional cube format. it also meant that the cube would be able to facilitate a rear-projection set up and ultimately a multitouch surface.
in the couple months before the event i did my research and developed a basic prototype of a diffused illumination (DI) projection. this is one of many multi-touch methods and one that works particularly well for large interactive surfaces. the downside of using DI is it is not as accurate as some of the other methods, although the timebomb interaction is based on movement detection and does not require a huge amount of precision as long as it could detect a change in the image.
there is a great thread on DI multitouch surfaces on the NUI website and is a great place to start when researching into the topic. the whole method works on infrared technology and pretty much boils down to the IR camera which blocks out visible light, so it doesn’t see the projection but it can see the people touching the surface of the projection.
i ended up going for a firefly mv black and white camera from point grey. its a firewire camera which has quite a lot of support in c++ land and appears to be a favorite amongst openframeworks users. the camera only comes as a body and so i also had to purchase a lens and an IR-filter to block out visible light. if you live in australia and need to kit up your computer vision camera, i recommend a company called adept, very knowledgeable and friendly chaps.
to complete the kit i got a couple IR spotlights from ebay for pretty cheap and i had a chance to test them against some top range IR lights that cost in the thousands ( thanks to the guys from adept ) and the results were surprisingly pretty much identical. just hop on ebay and search for ir illuminator but pay attention to the range and spread of the light, you’d want something with a decent angle of say 60 degrees and that can reach at least 40 meters.
finally you need something to project onto, a diffused material that can catch the light from the projector and be opaque enough to let IR light through so that the camera can see peoples movements on the other side. there are many specialised projection films which cost in the thousands to cover a large surface, some of which are outlined in this article, although since we only had a limited budget we went with drafting film, very cheap and a decent picture contrast.
building of the giant 2.5 meter cube was intense. spent 2 weeks worrying the whole thing would not hold and fall apart on some unsuspecting user, so i started reinforcing every panel of wood with metal brackets, especially the interactive surface which was constructed from 2 giant 10mm thick sheets of acrylic and i made sure the frame would be able to support it. in the end, the cube was SOLID! even the most enthusiastic of multitouch users could not rock it in the slightest.
on the day of the festival it was great to see people interacting with timebomb on the multitouch surface. people were really taking their time with the installation, trying to understand and harness its usability to control the time distortion effect to uncover the specific parts of the interactive graffiti wall. the one to one interaction scale was really the trick that made it all work and its whats so appealing about multitouch surfaces. its bridging the virtual gap and drawing the digital within the reach of the tangible.