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Figure 4. The result of a thematic query shows that this
door leads to the room of the GIS group.
Figure 5. A virtual guide leads the user through the
different fields of science in the exhibition room
of the information system of the Institute for
Photogrammetry (ifp).
3. UNREAL ENGINE 2
The Unreal Engine 2 (developed by Epic Games) is one of
the most widely used game engines to date. Because it is a
cross-platform solution, a broad range of products from PC
and video games to architectural visualisations have been
already developed with it. Being optimized for both indoor
and outdoor environments, it is one of the most modern and
versatile engines (see Unreal, 2004). Like most other game
engines, the technology is encapsulated in a binary runtime
library, while the game related parts of the Unreal games are
available as source code in a scripting language called
UnrealScript. The novel approach of Epic Games is that they
released the Unreal Engine 2 Runtime free for non-
commercial and educational use. This means that there is no
need to buy the game itself to run modifications and
applications that have been developed by the community.
The runtime even includes the map editor UnrealEd and
header files for C++ programmers. Beginners do find lots of
technical documents and even video tutorial that teach level
design, script programming and much more.
of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004
Figure 6. The Unreal Engine 2 is equally suited for indoor
and outdoor environments and produces stunning
landscape images in real-time.
4. OUTDOOR VISUALISATION USING
OPEN SOURCE LIBRARIES
So far, the focus of this article was on the visualisation of
indoor environments. Most geo-spatial data are, however,
rather outdoor data like e.g. digital height models or 3D city
models. There also exist powerful game engines that feature
outdoor rendering capabilities. The game engine Torque
(developed by GarageGames) combines both indoor and
outdoor visualisation modules into one software package
(Torque, 2004). But there also are powerful open source
game-like libraries available that make stunning outdoor
visualisation applications possible with very little effort.
These libraries have matured so that very little programming
effort is needed to create one's own visualisation application.
4.1 Open Scene Graph
The Open Scene Graph (OSG) is a cross-platform C++ /
OpenGL library for real-time visualisation. It has become a
powerful alternative to traditional tools like Performer and is
freely available under the GNU LGPL at (Osfield, 2004). The
library not only features high performance rendering
capabilities and excellent support for PC graphics
accelerators, but also offers stereo mode and a broad variety
of loaders for many common data formats. Several people
from the open source community already contributed plug-
ins and exporter for a number of popular modellers like 3D
Studio Max or Blender. For the purpose of moving through
the datasets, there exist camera manipulators that simulate
movement in a car or in an airplane. The drive camera
manipulator even uses collision detection so that the virtual
vehicle stays on the ground. OSG has been successfully used
in non-commercial games and virtual reality applications.
4.0 libMini
For the real-time visualisation of digital terrain models, a
continuous level-of-detail (C-LOD (Lindstrom et al., 1996))
approach is generally used. The C-LOD terrain rendering
library libMini recursively generates triangle fans during the
view-dependent generation of the quad-tree structured
triangulation (Roettger et al., 1998). The library is licensed
