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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV. Part B2. Istanbul 2004
activity and control its change accurately is a big problem for
the architecture and the urban designer. With the 3D city
models, we can construct the analytical models to simulate the
airflow activity.
32 Visual Quality Analvsis of Urban Space
The visual quality of urban space decide the pleasant degree of
human's mind which evoked by the vision. In practice, urban
design concerns with the physical arrangement of the basic
component that makes up the built environment at the level of
buildings, streets and landscape details. Therefore, visual
thinking of space is necessary in the design process. At thc
same time, the designer should take the user feeling as the
central point to analyse the location and the relationship of
different urban element. Visual analysis is no doubt a powerful
tool.
Through the virtual reality presentation of multi-dimensional
urban models we can carry out the “true” visual analysis that is
impossible to the traditional 2D GIS. The control of the height,
the colour and the style of the buildings, the evaluations of the
surrounding environment of the squares and the streets are also
available based on the visual impact analysis.
3.3 Structure Analysis of Urban Space
The analysis of the distribution of different function parts and
its proper place are possible through structure analysis of urban
space. Besides of this, structure analysis can also control the
change of the urban horizon contour and the building density.
Optimize the urban space structure is the import content of
urban morphology.
Spatial analysis is one of the key features that differentiates GIS
from other forms of spatial information systems such as spatial-
databases, computer cartography and computer aided design
(CAD). *Space syntax models the spatial configurations of
urban spaces by using a connectivity graph representation. Such
a configuration of space identifies patterns that can be used to
study urban structures and human behaviour. Over the past two
decades, space syntax theory has provided important
computational support for the development of spatial
morphological studies, in particular for the analysis of urban
systems" (Jiang B & Claramuntz C & Klarqvist B, 2000) .
In china, there are a lot of old cities like Lijiang of
Southwestern China. They formed with the natural order in a
long history. The urban space of it is full of life interest. Their
urban structure has high research worth. To analysis its urban
space structure can help us improve the space quality of present
cities.
4. 3D CITY MODELS BASED VISUAL ANALYSIS AND
PRESENTATION
For urban designer, the most significant application based on
3D city models is the visual analysis. In 3D dynamic virtual
environment, through the visibility computation according to
the simulation of human vision and the visual analysis for the
visible field can make the design process more realistic and
scientific.
4.1 Visual Analysis and The Visibility Computation
Visibility as a term---along with some related terms, such as
viewshed, visual quality, and visualization is very much evident
in the literature and practice of landscape planners and
designers. The visible field with certain eye-level and view-
La
angle can be computed, and it is the possible field we can see at
certain observe point. But what we can see does not equal to
what we seen. What we see among what is visible may depend
on the purpose and preconceptions (Stephen Ervin, Carl Steinitz,
2003) and depend on the weather, the colour and so on.
Visibility computation is the premise of the visual analysis. Of
course, the view field we seen is a subset of visible view-field.
In order to present the visual impact properly for urban design,
the visible field and the visual scene should be visualized, so
that the user can extract the visual information themselves and
implement the evaluation. Multi-mode and real-time dynamic
presentation is a good choice.
4.2 Multi-mode and Real-time Dynamic Presentation
In 3D dynamic environment, people usually can not ascertain
the right orientation because of the rich visual information.
However the 2D map can present the real orientation
efficiently, it is a powerful navigation tool in 3D dynamic
environment.
At the same time, the computed visible view-field should be
outstanding through the way of giving highlight or different
colour to the surface of visible object. This is the way we
present what we can see in 3D environment.
But how can we present what we have seen? The visual scene
at special viewpoint, which could change the eye-level and the
view-angle so that to fit different users, should also be
supported. The different user can get what they seen through
the custom-built visual scene.
The above description gives full presentation for the visual
analysis environment, and these three presentation modes may
be viewed in real-time through dynamic link. Here gives an
example to this kind of presentation as Figure (2, 3, 4) which
coexist in one interface. Only in this way the visual impact of
urban space can be fully expressed. In order to implement the
visual analysis effectively, the 3D city models should be
editable, and the space attribute of the models like colour,
texture and so on should be changeable.
LITT
RS) CEILI)
Figure 2 Stuttgart art gallery —plan
(the red point shows the orientation of observe point)
