Rear-Projection Setup
To make full use of the SDK, you will need a hardware setup which includes the relevant components. This section describes a very simple multi-touch display, with one camera and rear-projection system. For each component type we give some example products.
- Industrial FireWire “IIDC” camera with a large VGA sensor capable of delivering 60 frames per second. Recommendation: Basler Scout 640-74fm or Allied Vision Technologies Stingray F-033B. When buying the camera, make sure that you get a tripod adapter at the same time — many industrial cameras come without one.
- Tripod for the camera. You can also fix the camera without a tripod, but usually a tripod is the easiest thing to use.
- A 6mm lens for the camera. Recommendation: 6mm lens from Moritex or Pentax.
- Infrared-pass filter for the lens. The lens should pass the infrared light that you are using (usually 850 nanometers). Recommendation: Schneider “093” filter. Make sure that the filter size matches the threading in the lens. Lens suppliers usually also sell matching filters.
- Infrared light source. Recommendation: LED-based IR illuminators from MultiTouch Oy, or a series of halogen lights with photographic IR-pass filters. A 1,6 x 1,2 meter screen will require roughly 200 Watts of halogen-based infrared illumination, or about 70 Watts of LED-based infrared. Alternatively, a halogen light can be used as a cheap IR source.
- Data projector with 4/3 aspect ratio. For better resolution we recommend at least a 1024x768 projector with 3500 Lumens (1400x1050 resolution is preferable), but lesser projectors will do, depending on your budget.
- A computer with relevant FireWire connections. We usually use FireWire 800 cameras: if you do too, then you will probably need to get a PCI-Express FireWire 800 card for your computer. Recommendation: Any OHCI-compliant Firewire 800 PCI-E card. The computer should also have a decent graphics card, for example an NVidia card in the 200-300 Euro range. The PC should have any dual-core CPU (at least 1.5 GHz) and at least 1 GB of RAM. If you plan to use quad-core processors, we recommend AMDs Phenom line over Intel products, due to better performance.
- Display glass/plastic (1.6x1.2 meters, or less). Recommendation: Clear laminated 4-6mm safety glass, or high-grade plastic. For better image quality, use glass with antireflective coating.
- Rear-projection film. Recommendation: Gerriets Optitrans/Optilux. The film is generally placed behind the glass, so that users do not touch it directly.
- Frame for the screen. You may be able to buy a frame for your rear-projection screen, but few frames are strong enough to be used with touch-screens. Instead, you may need to buy or build a custom frame for the glass. The easiest materials for quickly building frames are wood and aluminium profiles. If you want to off-load this work to others, a typical trade-show stand maker should be able to build a simple solid frame with reasonable costs.
- Cloth, plastic or plywood to cover the top and sides of the display. The interior surfaces should be matt-black, for visual quality.
A practical layout for the components is shown above. This layout can be made more compact by using a mirror to reduce the projection distance. If the price of the components is too high, then it is easiest to just reduce the size of the display (section 8.1). In this simple setup the projector image matches the screen quite well, so we do not usually need to do any projector keystone correction. You should try to make the camera perpendicular to the screen. However, if this is not possible, the camera can be at an angle as camera image distortion is corrected anyway in the computer vision layer.