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Proceedings, XXth congress

Yonghak Song
Jie Shan
Geomatics Engineering, School of Civil Engineering, Purdue University
550 Stadium Mall Drive, West Lafayette, IN 47907-2051, USA — (song10, jshan)@ecn.purdue.edu
KEY WORDS: Photorealistic, 3-D, Geographic information systems, Visualization, Building modeling, Texture mapping.
Despite geospatial information systems are widely used in many different fields as a powerful tool for spatial analysis and decision-
making, their capabilities to handle realistic 3-D urban environment are very limited. The objective of this work is to integrate the
recent developments in 3-D modeling and visualization into GIS to enhance its 3-D capabilities. To achieve a photorealistic view,
building models are collected from a pair of aerial stereo images. Roof and wall textures are respectively obtained from ortho-
rectified aerial image and ground photography. This study is implemented by using ArcGIS as the work platform and ArcObjects
and Visual Basic as development tools. Presented in this paper are 3-D geometric modeling and its data structure, texture creation
and its association with the geometric model. As the results, photorealistic views of Purdue University campus are created and
rendered with ArcScene.
Three-dimensional (3-D) photorealistic visualization is one of
the most important functionalities in geospatial information
system (GIS). Such 3-D photorealistic visualization is able to
provide geospatial information for easy human perception. It is
helpful in geospatial information interpretation and the decision
making process (El-Hakim, 1998). Through the past years,
many successful models are developed to represent typical
geospatial features such as terrain, road, water body, vegetation
and many others. However, these are primarily 2- D or 2.5-D in
nature. 3-D features like buildings may not be represented well
by existing 2-D data structures and tools (Braun, et, al, 1995).
An effective geometric modeling approach is needed to model
the spatial location and the topology of buildings. In addition,
this model should also be extended to include other information
for buildings, such as attributes and image textures for query
and visualization purpose. Using image as texture will not only
increase the realism of the model but also enable the viewing of
details. It improves the interpretability; in other words, the
relationship between objects can be perceived easily and
reliably when photorealistic models are used in visualization
(Varshosaz, 2003). Although there are a lot of advanced studies
in computer graphics and commercial products in computer
industry, they do not typically handle geospatial information
and can not be easily integrated into existing GIS packages to
enhance its visualization capability, which is becoming a
demanding functionality in processing 3-D geospatial
information. On the other hand, GIS is a popular and standard
system with powerful 2-D spatial analysis capabilities.
However, its 3-D functionality is very limited where
photorealistic visualization is certainly a very useful addition.
The objective of this study is therefore to develop a 3-D data
structure, incorporate it into GIS and implement it for 3-D
photorealistic visualization to enhance current GIS capabilities.
We first discuss the suitability of the geometric building models
to be used for 3-D modeling and visualization. Then, a 3-D
geometric approach for building modeling is proposed. Under
this model, a building is composed of two parts; roof and
(vertical) walls. To achieve photorealistic visualization, these 3-
D geometric models are extended through texture mapping with
aerial photos for roof and ground photos for walls. In addition,
the algorithm associating geometric models with corresponding
texture images is discussed. After photorealistic building model
and appearance are achieved through modeling and texturing,
we discuss how to integrate 3D building model with other
geospatial data to generate the entire urban model. These
developments are integrated into ArcGIS package to enhance its
3-D visualization capabilities. Precise texture generation and
automatic texture mapping are discussed as an important
procedure to achieve high quality visualization effect. To
demonstrate and evaluate our developments, photorealistic
virtual campus models over Purdue University are presented.
Most GIS packages are designed for modeling terrain and other
2-D features. It is therefore not suitable for building modelling.
In such data models, the 3-rd dimension usually is obtained by
vertically extruding the 2-D footprint. In this approach, only
horizontally flat roofs or piecewise horizontally flat roofs can
be modeled. Hence we need a true 3-D model and incorporate it
into GIS.
There are many methods to model 3-D objects, such as wire-
frame model, surface model, and solid model. Usually GIS
packages use surface model and solid model is widely used in
the field of CAD (Computer Aided Design) and computer
graphics. Recent trend is to adopt the solid model to represent
buildings under CAD environment. The solid model such as
CSG (Constructive Solid Geometry) and B-rep (Boundary
representation) are very suitable to represent objects with
complex geometry and their physical characteristics. However,
it requires large memory and is relatively slow in displaying
because of the complex data structures and evaluation of the
data during rendering. Figure 1 shows the wire frame model and
the surface model for the same group of buildings. In the wire
frame model, edges are formed from vertices and no explicit
information exists about faces of the object. The dot symbol in