We currently build a new version of the HEyeWall, a large tiled rear projection setup.
With dimensions of 4m x 2m our version is one of the largest multi touch screens in the world.
With a resolution of approximately 8 Megapixels (4000 x 2000) a pixel has a size of 1 mm2. While we already implemented a soft edge blending, we are currently working on better hiding the seams, that are currently visible in the homogeneous regions in the photo below. A preview of the results is shown in the photo above.
Eventually, our FTIR (frustrated total internal reflection) multi touch system is running. From 140 infrared leds light enters the acrylic glas from the top and bottom. When a finger touches the screen, the light is scattered. Three cameras (752x480) behind the screen, equipped with infrared filters, detect the finger positions, transform them in the common normalized coordinate system and send the information to the application via network.
The tracking system is a derivative of our 3D optical tracking system for the DAVE. Its main advantage compared to other software is the native multiple camera support. Also, we compute a background image from several frames to avoid misdetections. This is important, since the acrylic glass bends when touched and visible reflections of the projectors move. This means, that at the moment we have a few blind spots. The background image is static at the moment but we plan to slowly update it at runtime to compensate for illumination changes of the environment.
We use 140 Infrared LEDs (SFH 421: peak at 880nm, driven with 90mA). They can be switched on and off by software, allowing to capture frames with ambient illumination only. The backprojection material is Translite Grey from Harkness Screens. The thin transparent cloth is bridal veil. We used Sorta Clear 40 with a little bit of Silicone Thinner, but the silicone has some defects and bubbles, unfortunately. We use 3 Pointgrey Firefly MV cameras with 752x480 each.
That's what the three infrared cameras images look like, when nobody is touching:
We recorded our first multi touch tests on the HEyeWall, have a look:
We also experimented with applications on our multi touch table.