I found a good link from a multitouch Dev Blog that contain an Post of the different between FTIR an DI screens.
Short: This are 2 diffrent solutions for multitouch devices, each with pros and cons
http://iad.projects.hgkz.ch/multitouch/?p=47
I really like his 180° Project, just take a look at it!
180:
http://iad.projects.zhdk.ch/multitouch/?page_id=3
Another Research project from IAD
tangent:
http://iad.projects.zhdk.ch/multitouch/?page_id=19
How to Build a DI Multitouch Device ->from libavg
https://www.libavg.de/wiki/index.php/Building_a_MultiTouch_Console
