Markerless Identification of Interactive Devices on Multi Touch Surfaces - Stefan Dippl
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This thesis focuses on recognition of and
interaction with markerless objects which may function as tools for
overview+detail or focus+context applications as described by Andy
Cockburn et al. [Cockburn et al.2008]. Markers usually ease the
recognition of objects but require special preparation of each object.
For applications exposed to public access this is an unwelcome
The general idea behind is comparable to existing multitouch projects  in this group but in contrast multiple self-sustaining devices are used that are in no other way but a wireless network connection attached to the computer running the actual application. For a failsafe and unique identification of those markerless devices it is necessary for the touch table to actually "see" the devices placed on its surface.
For this purpose a technique called "diffiuse illumination" (DI) is used.
Each device runs a client application which logs in to an application server via a Wifi connection. The application server is providing the device with a unique id and determining its position by evaluating data from the touch table while combining it with the data retrieved from the device's sensors. This information may be data from gyrometers or built-in cameras. For this thesis iPhones/iPod Touches are
used. The application running on the server decides whether to send plain image data as an overlay to the touch table's context or explanatory data like text+images in shape of HTML in order to enhance the user experience. Since multiple devices can be placed on the touch table, each device can serve a different purpose.
Imagine a route planning software displaying the calculated route on the touch table. By placing the handheld device on the table and moving it nearby the visual representation of the route, detailed navigation instructions are displayed on the device and can be stored to the device's memory. Additionally, contacts out of the device's address book close to the handheld's geo position appear on the map. Just to name a few of endless possibilities.
Cockburn, A., Karlson, A., and Bederson, B. B. 2008. A review of overview+detail, zooming, and focus+context interfaces. ACM Comput. Surv..