Johannes Luderschmidt’s Blog

The second multi-touch table, that I have built is called The Virttable, which stands for Versatile Illumination Research Touch Table.

This table is the property of the department for Design, Computer Sciences and Media (DCSM) of the Wiesbaden University of Applied Sciences, which provided me with the money for the components of the Virttable. Amongst others those parts include:

• a Panasonic PT AX 200 projector
• a Unibrain Fire-i Firewire camera
• lots of Osram SFH 485P infrared LEDs
• two panes of acrylic glass
• MDF boards for the box

The computer that I have used in the Virttable is my Mac Mini.

The Virttable (Versatile Illumination Touch Table)

The main goals for the Virttable have been…

1. a cheap setup
2. It can be put into a closet when it is not needed
3. It should be easily transportable in order to be able to exhibit the Virttable and innovative multi-touch software on it on fairs
4. All parts should be easily accessable in order to test different illumination techniques and to make the Virttable maintainable.
5. It should be usable with multi-touch and object input

The first point has been acheived: The whole setup did cost around 2000 Euro.

The second point has been achieved as well:

The Virttable in the closet

The third point has been enabled by the small form factor of the Virttable: the Virttable is 70 cm high, 74 cm wide and 54 cm deep. The wheels underneath the Virttable’s body make it rollable. The handles to the sides make it easy to carry and to attach tension belts in the trunk of a car.

The fourth point is provided by the lid and the hatch: The LEDs and the acrylic glass can be accessed via the lid and the projector, the computer and the camera can be accessed via the hatch.

The fifth point has been more complicated: A DI setup would have been easiest to support as well multi-touch as object interaction. However, DI is not as efficient as FTIR and thus we decided to make a hybrid approach by applying a mixture of DI and FTIR:

On the left there is no illumination. On the second photo the Virttable is FTIR illuminated. The third photo shows only DI illumination. The right photo shows the hybrid mixture of FTIR and DI: Touches are bright and precise and the fiducials of the objects are evenly lit.

We have also tried the DSI technology like it has been described by Tim Roth by using a Plexiglas EndLighten acrylic glass pane but the results have not been satisfying for us.

In the Virttable DI is provided by a few aluminum bars equipped with Osram SFH 485P LEDs underneath the tabletop. The bars are diagonally emitting their light onto the underside of the acrylic glass. Each LED is covered with a piece of masking tape to disperse its light evenly and to prevent hotspots. With this DI technique fiducials like those from the reactable can be used in this setup.

FTIR is provided by Osram SFH 485P LEDs in aluminum bars, which emit their light into the polished edges of the acrylic glass.

On the Mac Mini the Touchlib and reacTIVision is runnning. We are using alternately a Unibrain Fire-i and my Pointgrey Firefly MX Firewire camera in the Virttable.

Update: We have changed the illumination in the Virttable for MUCH brighter illumination. See our forum post at the nuigroup.

Here are some more pictures of the building process of the Virttable:

This entry was posted on Wednesday, November 5th, 2008 at 20:26 and is filed under Multi-touch, Portfolio. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.