International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
  
  
  
  
  
  
Figure 3 the visible field based on the visibility computation 
(the red-filled field shows what we MR 
rT rrrm- du 
  
  
Figure 4 The visual scene in which we can get what we seen 
4.3 Visual Spatial Analysis 
The visual analysis concept model and the analysis criterion 
come from the urban design guideline. Based on the 3DCM, the 
designer can carry out the alternating design in it, and embed 
their scheme into the 3DCM. For example, in some cases, the 
building should be back off the road red-line for some distance, 
and have the height limitation. Then the urban designer can 
convey their design result with the form of 3D control models, 
and evaluate the visual effect through the visual analysis. 
Selection of appropriate building types also could be guided by 
querying the associated database under the urban design 
guidelines. In Seattle, the urban design guideline includes the 
concept map of height limitation as shown in Figure 5 (Jin G J, 
2002). If we embed the quantify criteria of urban space like this 
in our analysis models, we can control the urban space more 
efficiently. 
328 
  
  
  
Figure5 the concept map of height control of downtown 
in Seattle (Jin G J, 2001) 
Through the height limitation of impressible area, the back-off 
distance control of the street building, or the open space control, 
the designer can either give an fully presentation for the urban 
design result or give a effectively control and analysis for the 
visual quality of urban space. 
"Enthusiasm for automated visibility analyses has grown 
significantly over the years because of marked improvements in 
hardware and software algorithms. The future advances in this 
field will eventually help solve the elusive visibility analyses in 
three-dimensional urban and natural environments" (Rana S, 
2003). 
5. CONCLUSION 
A successful decision support system should be easy to operate. 
The design process is complex, and it involve in all the aspect 
mentioned above, the physical quality, the visual quality, and 
the function quality of space. Generally, there need several 
analysis functions to do one decision. In one Spatial Decision 
Support Systems (SDSS), in order to adapt the design process, 
all the necessary analysis functions should be integrated. 
Computer-aided visualization can change the way we think and 
the way we work. For the architects and the planners, it can 
change the way of design. The ability to visualize potential 
modifications to the urban fabric and experience these changes 
in their actual context allows planners and designers to evaluate 
alternatives rapidly, in more detail, and for lower cost than 
through more traditional analysis. It also makes the results of 
planning process visible, allowing the public to view the 
proposed changes to their environment in a realistic fashion 
(Liggett R, 1997). 
[In moving from the abstract to the more concrete, 3DCM 
application may, provide planners and designers with tools to 
better consider the three dimensional space in the design 
process, as well as better control the form process of urban 
space by the urban governor and allow of more people to 
participate in it. What we need is to build the urban space 
control system based on the 3DCM. 
6. ACKNOWLEDGMENT 
This paper is supported by the open research fund of 
LIESMARS, No. (03)0404. 
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2003