MULTI TOUCH

INTERACTION

Parvika Singhal (101103071)

What is Multi-Touch?

Ability of a surface to recognize the presence of

more than one or more than two points of contact

with the surface

India’s First Laser Multi-touch Table is provided by

Team Zugard

The first devices to support Multi-touch were:

Mitsubishi Diamond Touch (2001)

Apple iPhone (January 9, 2007)

Microsoft PixelSense (May 29, 2007)

NORTD labs Open Source system CUBIT (multi-

touch) (2007)

ELAN eFinger

MULTI TOUCH DEVICES

Multi-Touch Interaction

Human interaction with a computer where

more than one finger can be used to provide

input at a time

Benefits of multi touch interaction:

Natural

Simultaneous multi user input

History

Illustration

Touch screen Technologies

Resistive

Capacitive

Surface Acoustic Wave

Infrared

Optical

Resistive Touch screen

Consist of a glass

or acrylic panel that

is coated with

electrically

conductive and

resistive layers

made with indium

tin oxide (ITO)

The thin layers are

separated by

invisible spacers.

Projected-Capacitive Touch

screen

During a touch, capacitance forms between

the finger and the sensor grid. The

embedded serial controller in the touch

screen calculates touch location

coordinates and transmits them to the

computer for processing.

Surface Acoustic Wave Touch

Two transducers placed in corners & two receivers in the opposite corners

Sound wave travels parallel to the edges of the glass. When the sound wave encounters the reflectors, the wave is transmitted from the transducers to the receivers.

Touch point is detected when a drop in the amplitude of the sound wave occurs.

Infrared Touch screen

Uses an array of X-Y infrared LED and photo detector pairs around the edges of the screen to detect a disruption in the pattern of LED beams.

LED beams cross each other which helps the sensors pick up the exact location of the touch.

Optical Touch screen

Infrared back lights

are placed in the

camera's field of

view on the other

side of the screen.

Touch shows up as

a shadow and

each pair of

cameras can then

be pinpointed to

locate the touch

Techniques

FTIR : Frustrated Total Internal

Reflection

DI : Diffused Illumination

DSI : Diffused Surface Illumination

LED LP : Led Laser Plane

LLP : Laser Light Plane

PRINCIPLE OF WORKING

Mesh of IR is generated on screen

Frustration is created on the surface if touched

Detected by the camera

Blobs (bright luminescent object) are created and sent to tracker

Tracker communicates with application

FTIR

Infrared light is placed and directed into the edges of an acrylic panel. The light is trapped within the acrylic by “total internal

reflection”. When a finger touches the acrylic surface, the infrared light is “frustrated” causing the light to escape internal

reflection and scatter downwards where it is seen by an infrared camera.

Diffused Illumination

Infrared light is shined at the screen below/above (Rear/Front DI) surface. When an object touches the surface it reflects more light than the diffuser or objects in the background; the extra light is sensed by a camera.

Diffused Surface Illumination

When a finger or object touches the diffuser, it lights up from the infrared light escaping from within and is seen by a camera below the surface.

Laser Light Plane (LLP)

Infrared light from single or multiple lasers shine above the surface. The laser plane of light is about 1mm thick and positioned very close to the touch surface. When a finger or object hits the light plane, the object lights up and is seen by an infrared camera below the surface.

Led Light Plane (LP)

The narrow angle LEDs are positioned just above the touch surface in order to create a plane of light. When a finger or object touches the light plane, it is illuminated and seen by a infrared camera below the surface.

Real Images

FTIR

DI

DSI

LLP

Led LP

Programming for the MT

CCV (Community Core Vision) is an open source C++ software package that contains code to analyze data from a camera, detect IR blobs from within the data, interpret that IR blob data, and generate TUIO events for the application to interpret.

Since most operating systems only expect one mouse click at any single time, a new event and protocol must be used to interpret any number of touches, the TUIO protocol.

TUIO (Tangible User Interface Object) : A protocol used for communicating the position, size, and relative velocity of blobs