Publication announcement:

Personal projected displays

Mark S. D. Ashdown

Technical report UCAM-CL-TR-585, University of Cambridge,
Computer Laboratory, March 2004, 150 pages.

This document is now available at

http://www.cl.cam.ac.uk/TechReports/UCAM-CL-TR-585.pdf

Abstract:

Since the inception of the personal computer, the interface presented to
users has been defined by the monitor screen, keyboard, and mouse, and
by the framework of the desktop metaphor. It is very different from a
physical desktop which has a large horizontal surface, allows paper
documents to be arranged, browsed, and annotated, and is controlled via
continuous movements with both hands. The desktop metaphor will not
scale to such a large display; the continuing profusion of paper, which
is used as much as ever, attests to its unsurpassed affordances as a
medium for manipulating documents; and despite its proven manual and
cognitive benefits, two-handed input is still not used in computer
interfaces.

I present a system called the Escritoire that uses a novel configuration
of overlapping projectors to create a large desk display that fills the
area of a conventional desk and also has a high resolution region in
front of the user for precise work. The projectors need not be
positioned exactly--the projected imagery is warped using standard 3D
video hardware to compensate for rough projector positioning and oblique
projection. Calibration involves computing planar homographies between
the 2D co-ordinate spaces of the warped textures, projector
framebuffers, desk, and input devices.

The video hardware can easily perform the necessary warping and achieves
30 frames per second for the dual-projector display. Oblique projection
has proved to be a solution to the problem of occlusion common to
front-projection systems. The combination of an electromagnetic
digitizer and an ultrasonic pen allows simultaneous input with two
hands. The pen for the non-dominant hand is simpler and coarser than
that for the dominant hand, reflecting the differing roles of the hands
in bimanual manipulation. I give a new algorithm for calibrating a pen,
that uses piecewise linear interpolation between control points. I also
give an algorithm to calibrate a wall display at distance using a device
whose position and orientation are tracked in three dimensions.

The Escritoire software is divided into a client that exploits the video
hardware and handles the input devices, and a server that processes
events and stores all of the system state. Multiple clients can connect
to a single server to support collaboration. Sheets of virtual paper on
the Escritoire can be put in piles which can be browsed and reordered.
As with physical paper this allows items to be arranged quickly and
informally, avoiding the premature work required to add an item to a
hierarchical file system. Another interface feature is pen traces, which
allow remote users to gesture to each other. I report the results of
tests with individuals and with pairs collaborating remotely.
Collaborating participants found an audio channel and the shared desk
surface much more useful than a video channel showing their faces.

The Escritoire is constructed from commodity components, and unlike
multi-projector display walls its cost is feasible for an individual
user and it fits into a normal office setting. It demonstrates a
hardware configuration, calibration algorithm, graphics warping process,
set of interface features, and distributed architecture that can make
personal projected displays a reality.

--
University of Cambridge, Computer Laboratory,
Technical Reports (ISSN 1476-2986)
http://www.cl.cam.ac.uk/TechReports/