Project dimensions

Since we've decided on a projector to use with the project, we now have concrete measurements on the projector size, the throw distance of the projector, and the screen size.  These dimensions are illustrated in this diagram:

The surface of the table will be about 3 feet off the ground, around waist level.  This should be a comfortable height for people to interact with the table while standing.  It should also be low enough for people to be able to interact with it sitting down and for shorter users to interact with it.

I used an online tool from Projector Central to calculate what screen sizes we can use with the given throw distance. The screen size (33" x 24.75") is one of the smallest screen sizes possible with the given projector, but is still relatively large (imagine a 40" TV).  The screen size also represents the projector's native aspect ratio of 4:3.  Finally, I made sure that the camera we buy can still see the entire screen from underneath for infrared blob tracking purposes.  The M12 Infrared Web Cam from EnvironmentalLights.com can easily see the entire surface with a 73 degree lens even if the camera is mounted 12" above the bottom of the touchscreen case.

Please let me know if you see any problems with this design, as I will be ordering the first round of hardware very soon!  I'm really excited to start the physical construction!

The projector has been chosen

Ultimately, we were able to limit number of projector choices down to four by looking only at short throw projectors that provided the required screen size.  Many of the high-end ultra short throw projectors actually produced a screen size that was far too large.  This eliminated many of the super heavy duty projectors to reveal smaller and cheaper models with great resolutions.


After making sure that the projector had a short enough throw and a small enough screen, we evaluated them on the quality of the image.


Brightness
Because the multitouch screen will likely be placed in a relatively brightly lit lobby, we needed to look at high-lumen projectors.  The lumens of the projectors we considered ranged from 2000 - 3000 ANSI.


Resolution
In order to choose a projector with a crisp, sharp picture, we evaluated each projector on resolution.  All of the projectors that we considered supported a resolution of at least 1080i, while only one projector supported 1080p.  However, since our particular project was not intended for action movies or fast-paced games, the difference between 1080i and 1080p was rather insignificant.


Lamp life
In order to ensure that our touchscreen is affordable in the long run, we had to look at the rated life of each projector's lamp.  Lamp life ranged from 2000 to 6000 hours (a 3x difference!).


Other considerations
We also considered other projector properties, such as contrast ratio (higher is better), inputs (preferably HDMI, DVI, or VGA), price, and whether it was 3D ready (could we combine 3D and multitouch?).


The Winner
Ultimately, the winning projector was the ViewSonic PJD7382 DLP Projector.

This projector had a brightness of 3000 ANSI, a 1080i resolution, a lamp life of 4000-6000 hours, a static contrast ratio of 2600:1, a dynamic contrast ratio of 3000:1, two VGA inputs, and is 3D ready.


With this projector in mind, we can now begin to finalize our dimensions!