How to build a Multi-Touch surface

Step 7 Alignment, alignment, alignment

The surface at this point is almost complete.  All that remains to do is to setup the projector and camera and align them so that they cover the same area and are not distorted.

First place the projector under the surface, with a slight angle of elevation so it is not projecting onto anything directly in-front / below it.  Next setup the front surface mirror so that it reflects the projector onto the acrylic layers above.  A front surface mirror is a necessity since an ordinary mirror will distort the image reducing the clarity of the image projected onto acrylic surface.  At this point the image will probably look more like a trapezoid, adjust the keystone  on the projector until a perfect rectangle is achieved.  You also may need to move the projector forwards or backwards, or the acrylic layers up and down in order to achieve the image size you desire.

Lastly, position the camera so it faces directly upwards towards the acrylic layers.  The camera should be placed directly in front of the projector under the center of the surface so it can pick up the entire desired area.

Comments

[lfields1]

I have been looking at the idea of trying to use a mirror to reduce the distance the camera needs to be from the screen. Have you tried this? I can't seem to find anyone that has. I would just do it myself but I am waiting on a computer that can handle multi touch. I have all the components except that.

[maewert]

I'm considering building this and I happen to have a broken rear projection TV that has a good front-surface mirror. I've seen other designs on the net that used mirrors to get a larger distance but have not done so myself. If you can get a front-surface mirror, then it should work.

[jck112]

I have not tried using a mirror, but your best bet is to use a super wide angle lens - such as one of these: http://peauproductions.com/store/index.php?main_page=index&cPath=26_4

[JDENredden]

Will this work? http://www.3m.com/mpro/mpro110/default.html

[jck112]

 The projector is heavily diffused by the rear projection layer.  So a pico/micro projector would only work if you are using the surface in a dimly lit environment.  If you plan on using the surface anywhere that their are windows then count on using a projector with >2000 lumens.

[tegreenleaf]

 Is there a limit to the size of the screen?  I know the dimensions used here are for the camera you used, but can you apply the same techniques used here to a larger surface with a bigger and/or better web camera and projector? 

[critterfluffy]

or multiple projectors and cameras?