BASICALLY...

A Touchpanel is a sensor system that returns: (x,y) as analog z (presence) as digital optionally returns: z as analog multitouch ID When creating a touchpanel, consider: Application (singletouch vs. multitouch, finger vs. object) Environment (lighting, space, display type) Cost Some good references: http://www.research.ibm.com/journal/sj/393/part3/paradiso.html http://www.protechservices.ie/touch-panel.htm http://tangible.media.mit.edu/ http://www.pixelsumo.com/tags/tangible/

TYPES OF COMMERCIAL TOUCHPANELS

http://www.protechservices.ie/touch-panel.htm Resistive (any object - smart board, AV tps - not terribly sensitive, wears easily) Capacitive (finger only - computer touch pads, very robust) SAW (Surface Acoustic Wave - any object - gaining popularity, expensive) DST (also sound waves. bad. stay away.) IR (beam arrays. Any object. very robust, long lasting, expensive, doesn't scale)

CAMERA/MACHINE VISION
most flexible (in some ways), but necessitates limiting environment   lighting (!!)   placement machine vision looks for:   change over time   edge detection   blob   shape within Region O' Interest (ROI) Note: Projectors generally have little to no IR, so generally good to use IR lighting Particulars: Requires lots of software interpretation generally need 2 computers - one for machine vision, one for display Allow lots of R & D - make physical model try and think of "trick" to make finger visible: ie. active IR LED Sort of scalable. Need some depth for camera	Benefits: cheap (webcams are $30) Lots of research out there (MIT, CMU) Lots of high level software and off the shelf stuff: Track Them Colors for Director JMyron/WebCamXtra for Java/Director Cyclops for MAX/MSP/Jitter SoftVN for MAX/MSP Presense Plus Pro system by Banner Engineering Drawbacks: Unreliable - lighting huge factor software/CPU intensive (go through lots of data) Generally setup time is tricky and difficult
1. Side "Squinting"
need to use (and evaluate) 2 cams - for instance 1 does x and 1 does y Need wide angle lens make sure no comes between cam and touch surface Application:   multitouch   analog z Environment:   can use vert or horiz, fnt or rear   Need controlled space around installation   can use array of IR leds to provide reflection.
2. Rear Camera
1 cam with coordinate system mapped to touch surface Usually with rear projection usually IR lighting (760 nm and about) Easy to evaluate, but becomes a lighting problem. You need really smooth lighting. In sunlight less IR than visible light, but plenty of it. Projectors generally have almost no IR Flourescent good. Halogen bad. Application:   *sometimes* analog z   multitouch Environment:   dark room or no IR lighting   lots of rear space   better if vertical
Danny Rozin - "Easel" - 1998 Active IR LED in Paintbrush	Jeff Han - 2005 Multi-Touch Sensing through Frustrated Total Internal Reflection IR LED Side Lighting
Alvaro Casinelli - Khronos Projector - 2005 Rear Lit with Flexible Sreen	Graham Plumb/Gyroscope Inc - "Conservation Lab" - 2005 Bishop Museum, Honolulu Technology by Sasha Harris-Cronin/BBI Engineering Rear Lit by reflected bounce
3. Stereoscopic Vision
2 cams with coordinate systems mapped to each other requires the most intensive software/math Once working, pretty robust Application:   coarse analog z   multitouch Environment:   front or rear   better if horizontal (easier to have cams above)   controlled lighting (but *can* do by measuring change in image)	West Office Exhibition Design - "Datastream" - 2006 Cadence Design Systems Technology by BBI Engineering

RFID
like Wacom Tablet Application: object only, not finger multitouch limited Z and tilt/direction. provides ID (coded objects) Environment: Can use in any ambient conditions. Only front projection surface needs to be powered Particulars: requires a large amount of hardware/DSP knowledge. Can't really triangulate at that size. Has to be full underlayer.	Benefits: if you have the hardware knowledge, relatively cheap. Very accurate. Downsides: If you can't build your own hardware, expensive. Lots of RF knowledge reauired. not scalable Off the shelf: wacom
James Patten, et al - Sensetable - 2001

Sound
active - send out ultrasonic "ping" or standing wave and measure results passive - look for a tap on a resonant surface Application: Single touch limited z only in active object or finger Environment: Must use resonant surface Have to have transducers on front of surface Noise is sometimes a problem	Benefits: Very cheap hardware lighting insensitive Downsides: difficult software. difficult to hide hardware
Josh Paradiso, et al - Tap Tracker - 2000

BEAM ARRAY aka. LIGHT CURTAIN
Use two set of beam curtains to create X and Y. Use narrow beam lensed IR LEDs and phototransitors. Application: can be object or finger limited multitouch (due to occlusion) Environment: in front of the surface pretty light resistant Benefits: simple idea. tricky, but doable. reliable once set up Downsides: Not really scalable. Tedious to make. off the shelf: banner engineering light curtains
West Office Exhibition Design - "Waterfall" - 2002 San Francisco Federal Reserve Bank Technology by Sasha Harris-Cronin/BBI Engineering

CAPACITIVE SENSORS
Either use individual capacitive sensors per "hot spot" or an array of cap sensors. Application: only fingers multitouch Environment: completely environment unaware can be front or rear screen Benefits: discreet. analog z relatively reliable Downsides: Not terribly scalable. can be expensive (though getting cheaper) off the shelf: Lemur QProx Sensors Cypress capSense PSoCs	DECEASED!

OTHER STUFF

Scanning Laser Rangefinder expensive, bad for your eyes, hard to find one with the right range Jeff Han's LED multitouch pad interesting, but not very practical power your use and use them as a capacitor