Open Source Interface

Getting Started With MultiTouch

2008-05-22T22:49:12-05:00

Getting Started With MultiTouch

Multitouch Techniques

FTIR and DI are the two main technologies used in NUIGroup (Information on alternative techniques will be posted at a later time). Specific Parts (brands, types, etc.) and techniques for completion can be found on the rest of the forum.

Frustrated Total Internal Reflection (FTIR):

Infrared light is shined into the side of an acrylic panel (most often by shinning IR LEDs on the sides of the acrylic). The light is trapped inside the acrylic by internal reflection. When a finger touches the acrylic surface this light is “frustrated” causing the light to scatter downwards where it is picked up by an infrared camera.

A silicone rubber layer is often used as a “compliant surface” to help improve dragging and sensitivity of the device. When touching bare acrylic, one must press hard or have oily fingers in order to set off the FTIR effect. With a complaint surface (like silicone rubber) the sensitivity is greatly improved.

FTIR Parts List:

o Acrylic/Polycarbonate/Plexiglass
o Infrared LEDs (or similar infrared light source)
o Compliant Surface (silicone rubber ie. Sorta Clear 40, Elastosil, Lexel, etc. )
o Projection Surface (Rosco Grey, Vellum, Mylar, other, etc.)
o Infrared Camera/Modified Webcam

Diffused Illumination (DI):

Diffused Illumination comes in two main forms. Front Diffused Illumination and Rear Diffused Illumination. Both techniques use the same basic principles.

Rear DI:

Infrared light is shined at the screen from below the touch surface. A diffuser is placed on top or on bottom of the touch 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. Depending on the diffuser, this method can also detect hover and objects placed on the surface.

Rear DI Parts List:

o Clear sturdy clear surface (Glass, Acrylic, Polycarbonate, Plexiglass, etc.)
o Infrared Illuminator (Infrared LEDs, Infrared Illuminator, etc.)
o Diffuser/Projection Surface (Vellum, Mylar, Lee Filter, other, etc.) *Note: The Diffuser/Projection Surface must let some light through.
o Infrared Camera/Modified Webcam

Front DI:

Infrared light (often from the ambient surroundings) is shined at the screen from above the touch surface. A diffuser is placed on top or on bottom of the touch surface. When an object touches the surface, a shadow is created in the position of the object. The camera senses this shadow.

Front DI Parts List:

o Clear sturdy clear surface (Glass, Acrylic, Polycarbonate, Plexiglas, etc.)
o Diffuser/Projection Surface (Vellum, Mylar, Lee Filter, other, etc.) *Note: The Diffuser/Projection Surface must let some light through.
o Infrared Camera/Modified Webcam

Optional:
o Infrared Illuminator (Infrared LEDs, Infrared Illuminator, etc.)

Laser Light Plane (LLP):

Infrared light from a laser(s) is shined just above the surface. The laser plane of light is about 1mm thick and is positioned right above the surface, when the finger just touches it, it will hit the tip of the finger which will register as a IR blob.

LLP Parts List:

o Clear, flat surface (Glass, Acrylic, Polycarbonate, Plexiglass, etc.)
o Infrared Laser(s)
o Line Generating Lens
o Projection Surface
o Infrared Camera/Modified Webcam

Diffused Surface Illumination (DSI):

DSI uses a special acylic to distribute the IR evenly across the surface. Basically use your standard FTIR setup with an LED Frame (no compliant silicone surface needed), and just switch to a special acrylic. This acrylic uses small particles that are inside the material, acting like thousands of small mirrors. When you shine IR light into the edges of this material, the light gets redirected and spread to the surface of the acrylic. The effect is similar to DI, but with even illumination, no hotspots, and same setup process as FTIR.

DSI Parts List:

o EndLighten Acrylic
o LEDs
o Projection Surface (tracing paper, lee filter, geriets optitrans , etc);
o Infrared Camera/Modified Webcam

Technique Comparison

A frequent question is “What is the best technique?” Unfortunately, there is no simple answer. Each technique has it’s pro and cons. The answer is less about what is best and more about what is best for you (which only you can answer).

The General consensus is: If you need object, fiducial, and hovering recognition than rear DI is most likely for you. If you only need a robust and reliable finger recognition, than FTIR is a great choice. Front DI, although the simplest to build, is rarely used as a permanent setup since it heavily relies on the surrounding environment.

FTIR:

Pros:

o An enclosed box is not required
o Blobs have strong contrast
o Allows for varying blob pressure
o With a compliant surface, it can be used with something as small as a pen tip

Cons:

o Setup calls for some type of LED frame (soldering required)
o Requires a compliant surface (silicone rubber) for proper use
o Cannot recognize objects or fiducial markers
o Cannot use a glass surface

Rear DI:

Pros:

o No need for a compliant surface, just an diffuser/projection surface on top/bottom
o Can use any transparent material like glass (not just acrylic)
o No LED frame required
o No soldering (you can buy the IR-Illuminators ready to go)
o Simple setup
o Can track objects, fingers, fiducials, hovering

Cons:

o Difficult to get even illumination
o Blobs have lower contrast (harder to pick up by software)
o Greater chance of ‘false blobs’
o Enclosed box is required

Front DI:

Pros:

o No need for a compliant surface, just an diffuser/projection surface on top/bottom
o Can use any transparent material like glass (not just acrylic)
o No LED frame required
o No soldering (you can buy the IR-Illuminators ready to go)
o Can track fingers and hovering
o An enclosed box is not required
o Simplest setup

Cons:

o Cannot track objects and fiducials
o Difficult to get even illumination
o Greater chance of ‘false blobs’
o Not as reliable (relies heavily on ambient lighting environment)

LLP:

Pros:

o No compliant surface (silicone)
o Can use any transparent material like glass (not just acrylic)
o No LED frame required
o An enclosed box is not required
o Simplest setup
o Could be slightly cheaper than other techniques

Cons:

o Cannot track traditional objects and fiducials
o Not truly pressure sensitive (since light intensity doesn’t change with pressure).
o Can cause occlusion if only using 1 or 2 lasers where light hitting one finger blocks another finger from receiving light.

DSI:

Pros:

o No compliant surface (silicone)
o Can easily switch back and forth between DI (DSI) and FTIR
o Can detect objects, hovering, and fiducials
o Is pressure sensitive
o No hotspots
o even finger/object illumination throughout the surface

Cons:

o Endlighten Acrylic costs more than regular acrylic (but the some of the cost can be made up since no IR illuminators are needed)
o Blobs have lower contrast (harder to pick up by software) than FTIR and LLP

Microsoft Surface - Raw Data Visualizer

2008-10-07T01:50:34-05:00

[youtube]iIbgnDfEU-E[/youtube]

I wonder how did they make so bright blobs?
It seems like the surface they are using passes IR light completly through without any reflection.
Any ideas what kind of material they could be using?

Blobs stay after removing fingers

2008-10-06T03:12:00-05:00

Hey hey,

does anybody know, why my blobs stay at the camera display still after touching? If I touch the screen and slide my fingers over the screen, then remove all my fingers ... the lines where I moved stay as blobs for a long time. For my setup I used for that test the layers:

- Rosco Grey
- Silicon Rubber (Elastosil 4641)
- Acrylic

If I use a standard Mylar instead of Rosco, the Blobs remove very fast, when I remove my fingers. Does anybody has an idea, what´s the reason for that? Or is that normal with just rosco on the Silicon Rubber?
Thanks already.

Richard

DI setup… edit: problems with chosing surface..

2008-09-23T15:32:37-05:00

Hey

Iam about to make a DI setup table and wanted to know if the stuff I have is okay…

I wanted to build the table like Tinkermans

http://nuigroup.com/forums/viewthread/2089/P30/

I have this:
Projektor (Infocus x3 or x2 can’t remember)

Frossed glas

3x 140 IR Led Infrared Illuminator 880nm
http://cgi.ebay.de/140-IR-Led-Infrared-Illuminator-for-CCTV-Camera-System_W0QQitemZ140268712649QQcmdZViewItem?hash=item140268712649&_trksid=p3286.m63.l1177

Xbox Live camera

Infrared Filter wavelength 850nm for 58mm Cameras
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=120178570544&ssPageName=ADME:B:EOIBSA:DE:11

Mirror, wood and alu for reflektor effect.

Do you see any problems?

Another thing where would be a good place to mount the ir illuminator in a table like Tinkermans? not direct at both the camera and the glass right?

Hoping for some reply..
Ferrari_man
(sorry for the spelling)

USB Network Hub

2008-10-06T01:13:35-05:00

Hello all,

I’m finally getting back to building my DI table. I plan to use the Toshiba TDP-EW25U projector and because it has network/wifi connectivity i’ve been thinking it would be great to send the webcam over the network as well. I was wondering if any of you have tried this and what kind of USB network hub works well with webcams? I’m probably going to use the Xbox Live Vision as it seems like an easy camera to work with.

Building My own Multi Touch LCD

2008-10-05T01:30:36-05:00

hi, I am very new in building my own stuff,

but the Multi-Touch technolgy is something I always dreamed of , And i really want to make it for my self,

I search all around the internet, trying to find out the way to build it,

but still I am very confused, I was able to build mttable, since this was really easy,

now i want to make it with my LCD monitor,

I saw this picture, but i don’t get how, the camara can see through my lcd monitor,

can somebody tell how to build the LCD monitor, like MS surface ??

thank you so much for taking time to read my topic,

sorry for my lack of english.

MTmini touchlib for REAR DI? And some problems

2008-10-04T22:08:05-05:00

Exists a version of the MTmini touchlib for REAR DI?

I can’t get clear blobs with my touchtable. I’m using a sheet of tracing paper and 100 leds in my config( 60x60cm screen).
When I can get blobs, the palm of hand also appears !

Thanks

I’ve got the parts… which way should I assemble them

2008-10-04T14:13:37-05:00

I’ve got an 18x24 inch 5mm thick sheet of acryllic, and two home-made arrays of 24 IR LEDs each (each array is a straight line). My acryllic has relatively non-clear edges. Should I make an FTIR table or a DI table? Which one would be easier to make at this point?

Where to buy… in FRANCE!!

2008-09-13T14:42:07-05:00

Hello,
After many researches on the Internet to find parts to make my own MT Screen, I nearly find nothing in order to be deliver in FRANCE where I live!!
Is thre anyone who lives also in FRANCE and know where to buy for example the compliant and the projection surfaces? Or anyone else who knows a website who proposes a delivering in France?

Thanks a lot

School Project : FTIR MT

2008-10-03T17:23:53-05:00

Dear,

I’m a student from Belgium, and this school year I gonna make a FTIR multi-touch table.
I never made one before so I need some advise. After reading a lot on this forum I think,
I’m capable of making one. I gonna update weekly/monthly and hopefully I got the nicest project :D.

What do I have right at the moment ?:

A prototype design of the woodwork:

200 Ir LED’s:
http://www.samenkopen.net/action_product/965623/748561

A projector:
NEC VT660
http://www.necvis.com/Documents/UserMan/VT460_560_660usermanual.pdf

The rest will come soon, but I actually have 2 questions:
-Do I have the right equipment so far?
-How can I know which distance the project has to throw for filling the whole screen?

Thx in advance,
Grtz Dietger.