The projection environment of PLACE consists of a cylindrical projection screen and a
rotating platform in the center that carries a wide-angle three-projector system fed by
an SGI-Onyx computer. The distortion caused by the projection onto the cylindrical
surface is compensated by a predistortion of the generated imagery by means of software
that acts on the object coordinates of the virtual scene and effectively emulates an
idealized cylindrical projection system. The vertical edges of the individual projected
images are faded to black gradually in order to minimize the visible gaps between
adjacent images. The user interface, a modified video camera, controls the navigation in
the virtual environment. The rotation on the camera stand controls the orientation of
the virtual viewer and of the rotating platform, the zoom buttons of the camera control
forward and backward travel speed. A third button allows centering of the viewer inside
one of the textured objects he has entered. A microphone attached to the camera triggers
the emission of preselected text in form of 3D floating characters into the scene. The
virtual environment reflects the projection environment. It consists of cylindrical
objects textured with panoramic photographs whose dimensions correspond to those of the
projection environment. These objects are located in an endless plane and they are
repeated infinitely in all directions. The text that is emitted when triggered by the
camera microphone appears in full words in textual order in form of 3D block characters.
These appear in front of the virtual viewer and travel off to the left at constant
speed. The viewer's travel speed doesn't add to the emission speed, and thus it appears
to the viewer that the text's letters appear compressed or expanded, depending on the
momentary travel and rotation speed. The characters are reflected when reaching a
certain radial distance from the viewer, and they start to fade out and disappear after
a short period of time, to make place for new characters triggered by acoustic events.
EVE, a large stereo projection system inside a spherical screen, has been interfaced to
PLACE by means of a network connection between the graphics computer of PLACE and
another SGI-Onyx computer generating the imagery for EVE. The software is an extension
of the program written for PLACE. It uses a custom protocol based on TCP/IP to
communicate the virtual viewer position and the text emission from the master system
located in PLACE to the slave system in EVE. The master side of the software works as a
server, i.e. clients can connect to and disconnect from it at any time. A viewer for
undistorted stereo display had to be added to the various PLACE viewers designed for
different symmetric and assymetric projector cones and cylindrical screens on one hand
and different idealized cylindric projections on the other hand. The predistortion of
the data for spherical projection was not implemented since the relatively small field
of view of the EVE projectors and the fact that there are no multiple adjacent
projectors do not urgently require it. Once there will be multiple projectors, this
predistortion becomes necessary, too, and is based on the same principle as the original
cylindrical predistortion in PLACE. The projector head of EVE carrying the stereo
projector pair is controlled by a human viewer who carries an infrared beam attached to
his head. The system is constructed to follow the infrared spot on the EVE projection
surface with a very short delay, and the corresponding orientation data is transmitted
from the projector controller system to the graphics computer via another TCP/IP
connection. The rePLACEd software on the EVE side uses this rotation information to
orient the virtual viewer. The virtual viewer's position is thus controlled in response
to user input from two sides. The EVE visitor is positioned in space by the visitor in
the cylindrical environment navigating by means of the modified video camera interface,
and sees a direction corresponding to his or her own physical viewing direction inside
EVE. Whereas the rePLACEd 3D software that is based on Silicon Graphics' GL library is
tailored very closely to the application, the principle of the cylindrical projection
environment opens a wide range of possibilities. The environment can be applied as an
all-purpose viewing environment useful for general 3D scenery. Due to its spatial
properties, it is very communicative by allowing a rather large group of people to share
the virtual presence. It seems ideal for presentation and exploration of large,
structurally planar virtual worlds such as gardens or cities. Of course, scenes with a
bigger extent in the vertical direction can be viewed, too, but then the distortion
stemming from the idealized mathematical cylindrical projection that is required in this
environment becomes noticeable. A vertical angle of ¦45¦ can be regarded as a natural
limit. The plane seems to be a suitable space for multiple presence in a virtual
environment, since the participants can see each other from far away. The idea of
infinite replication of the scene could be applied to the participant's avatars as well.
One can travel without any limits but will encounter infinitely many representants of
the co-inhabitants of the scene. The positional control that the EVE viewer experiences
can be seen as one of many possibilities how participants in a virtual event can share a
common viewpoint. The bus-driver metaphor used here is a quite natural way to achieve
this goal. Others like a group exploring unknown terrain as individually moving viewers
have proven successful, too.