ınbul 2004
| the area
re inside
- Node.
for each
ct so the
ne object
essary to
> parts of
on
o an IFS-
scene, all
e created
a surface
the parcel
nected to
rd can be
way you
f the land
ain, and it
red in the
ad.
y example
ided with
how what
ing walls
navigates
with their
s in green
1g a table,
e).
le is used
's, the use
esponding
L Viewer
s color.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B-YF. Istanbul 2004
Figure 4. Thematic query based on USE from attribute table.
(O Stadtmessungsamt Stuttgart)
3. VIRTUAL REALITY
The second part of the project is focussed on Virtual Reality.
Virtual Reality is an immersive experience in which participants
wear tracked, head-mounted displays to visualize, and listen to
3-D sounds and are free to explore and interact within a 3-D
world. This part of project is aimed to allow user to interact
with the world and display the attributes as text, while the user
is still navigating around in immersive environment like
C.A.V.E or Responsive Workbench.
VR is multi-modal that defines the more hardware oriented
interface definition as the combination and cooperation of
various input and output channels, which distinguishes the
interface channels more from the point of media instead of the
sensory perception. Dynamic behaviour introduces the notion of
time into virtual environments. A highly interactive system has
to deal with time in general and specifically with variable time
frames and their synchronization. Responsive virtual
environments should operate in real-time, that is, the response
time and update rate of the system is high enough so that the
boundary between user and virtual environment, the so-called
interface, seems to vanish. This property is one of the major
differences between VR systems and other 3D systems.
3.1 Tools
Whether they're images, 3-D sounds, or tactile vibrations, all
aspects of VR must be coordinated and precisely delivered
otherwise confusion will result. The computer system and
external hardware that supply effectors (HMD or C.A.V.E) with
the necessary sensory information comprise the reality engine
(Pimentel and Teixeira 1993).
This project has been tested in the C.A.V.E at Fraunhofer
Research Institite for Industrial Engineering IAO in Stuttgart
using the application software "Lightning VR" developed by
them. Its core component is a database called object pool. The
interactivity and the behaviour can be introduced with
functional objects, so-called scripts and communication
channels, so-called routes. These communication channels
define application specific event propagation and therefore the
interactivity (Blach et al 1998).
Tcl/Tk programming language is used for interaction with
lightning, as it is easy to integrate into other systems
(Ousterhout, 1993).
25
3.2 Input Data
Input geometry data for this application is the same VRML
model converted from the ASCIH file in the above web3D
project. The model consists of buildings and terrain information
of Stuttgart city. Each building has unique name defined to the
node that is describing the geometry. Lightning VR uses
LibVRML97 for reading and displaying VRML files, which is a
portable C++ class library (Chris Morley, 2002). This library
can access the properties like position, orientation, scale, centre
of bounding box etc. of the world files in scene.
The attribute information concerned to the objects, which was
purposefully created and saved as text file called “connection
table” in the first part of project. This connection table has the
information like Definition name, x, y, z, House name etc. Here
definition name will act as primary key in connecting spatial
and non-spatial data.
3.3 Selection of building
The input device can be a 3D mouse or glove etc, for the
identification of objects in the virtual environment. The
properties like position, orientation, scale etc, of input device is
calculated by motion sensor in Lightning. In order to make
input device a selecting tool, a ray has to be made active using
ItSelectRay. It's a library under Lightning server, which is
invisible. It can sense the objects hit and returns field values
like first object hit, position & orientation, count of hit objects,
etc, to the application. It is quite similar to pick() method of
Cortona in Web3D project. The position and orientation values
of ray were now routed (borrowed) from motion sensors
properties, to make the input instrument act as a selecting tool.
Now this ray (cursor) can be used to sense any object in virtual
world. While moving the input device over building, it senses
the object, recognizes it and sends the definition (name) to
NodeHitOut property of SelectRay. This definition name will be
used as primary key to match with the concerned attribute data
that is stored in the text file.
3.4 Connection to attribute data
The attribute data of the model is available as separate text file.
The program written in Tcl will read the text file line by line
and check if the definition name from the ray, matches with first
field of the text file. Once matched, the whole line of the text
file is converted to text element using ltText property of
Lightning and displayed over the object, which you pointed in
runtime scene situation, as shown in figure 5.
Powered By sgi
OpenGL Performer
Figure 5. Selection and attribute display of the building
(O Stadtmessungsamt Stuttgart)
