My visit with Laurence Muller

Laurence Muller is a master of Grid Computing student at the Universiteit of Amsterdam, he has been researching multi-touch screens since the summer of 2007. I visited him at his school on friday to see and experience his setup and play with the applications he could offer me. A big thanks to him for answering my endless amount of questions.

The setup he eventually choose was that of RI (Rear Illumination), which basicly means that the infrared light comes from behind instead of in the table top. The reason he choose this setup is because the FTIR setup can't recognize objects and he needed that.

First of all he looked at the photo's on my website and asked himself the question rather or not the camera was seeying IR properly. So I asked him what he used and he used a FireWire webcam from unibrain called the Fire-i Board Camera Color. A lot of people that are building multi-touch devices confirm that firewire camera's are the way to go, because they can process streaming data much faster. There were also some people that claim that USB is also slower because it uses a compression techniques to get the images across the (narrow) USB bus.

I am also going to order my Fire-i Board Camera Color (€68) on monday, together with a 4.3mm standard lens without the IR coating (€12).

The camera then only needs a proper bandpass filter to filter out the visible light and only let the infrared light come in. I will be using black photonegatives for this.

So next, the frame. After the whole frame has been build, with the wires, the leds and the plexiglas I should already detect blobs from the fingers. With touchlib running on the computer I could already test it out. For tracing and dragging of objects however, this setup needs to be improved for better performance. From what I've been told when you drag your finger across the glass there will be more air between the finger and the glass making the blob less clear. To get rid of this, you will need a silicon, like Sort a Clear 40, layer. On top of the silicon you will place the diffuse material, the nuigroup stated that rosco grey is the best way to go, but very hard to get as well. The cheapest solution would be tracing paper. The good thing about Rosco grey is that it blocks IR light from the outside, making the table more usable in different kind of environments.

Alright to put things into perspective, the layers will look as follows:
- Finger
- Projection Screen
- Silicon Rubber Sheet
- Acrylic

Last but not least, Laurence told me that in the meantime I could already look into developing applications for my future touchscreen by using the reactivision tuio simulator to simulate finger touches.

Download the latest version of Touchlib from http://nuigroup.com/touchlib/downloads/
Download the latest version of Reactable from http://reactable.iua.upf.edu/?software