ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
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remote sensing technologies, the amount of image data has 
dramatically increased, and has garnered more and more 
attention. Besides 4D techniques, creating UDSS need other 
new technologies such as 3D city model (cybercity) and urban 
geographical information system(UGIS). 
4D and associated enabling technologies offers new and 
exciting opportunities to create 3D city model. Virtual reality(VR) 
technique can construct a 3D environment. Decision-makers and 
users can walk through 3D environment, see newly planned 
buildings and appreciate changes in the landscape. 
Fig.2 creating DEM using digital automatic photogrammetry 
The other associated technology is UGIS. The use of UGIS shifts 
from 2D to 3D modeling and analysis. Buildings and 
constructions are modeled with digital photogrammmetrical 
system (4D products) and linked to data in the UGIS. The 3D 
information is used to calculate volumes, distances, sound 
contours, shadowing, line-of- sight, etc. 
Once the 3D city model has reached the status of s 
well-engineered proposal, it will be converted into a form to be 
present to all participants in the urban decision-making process. 
This can be either through detail designing, DEM and DOM 
rending, or with very detailed and realistic scale models. The 
different variants and alternatives will have to be compared and 
their consequences and performances clearly outlined for each 
the different participants. The more realistic the presentation can 
be, the better the plan is communicated. 
UGIS analysis involves the impact of the new design on its 
environment. The design is evaluate with respect to its 
exploration, maintenance, usability and environmental quality. 
Visual analysis is the main task at this stage of the planning 
process and a more realistic visualization will only improve the 
presentation of the plans. Form this analysis of the planning 
process, the most important requirement for UDSS are 
possibilities for 3D analysis, a good visualization and interaction 
with the data. 
Fig.3 creating DOM using DPS and remote sensing 
3. An example of application of 4D and associated enabling 
technologies for UDSS 
There are many applications of 4D and associated enabling 
technologies for UDSS. Flood risk analysis is one of the 
applications. Floods are the costliest hazard in the world and 
account for the economic losses resulting from natural 
catastrophes (Munich Re, 1997). Riverine flood is a major 
natural hazard in China. For example, The Yangze River Flood in 
1998. UDSS preventing flood is becoming more and more 
important. Information resources of flood risk analysis model are 
collected from 4D and relevant investigation and statistics data. 
Flood risk analysis can be divided in three phases: 
(1) . Preliminary stage of preventing flood 
During this phase, the problem of flood is studied and all 
relevant information is collected, especially historical flood data, 
hydrological data, 4D products. Flood risk analysis model is 
created using 4D and relevant technologies. Two main tasks are 
done. The first task is flood risk analysis. Historical flood data 
can be represent and displayed under 4D and UGIS environment. 
So flood risk analysis and dangerous area predicting can be 
made in advance. The second task is making a preventing flood 
plan. 
(2) . During the stage of flooding 
In the phase, flood risk analysis model will play very 
important role. The flood surface and damage information can be 
displayed under 4D and UGIS environment. For example, raw 
flood surface location can be predicted by real-time flood risk 
analysis model, (figure 4). Decision-maker have many things to 
do in the short time, making rescue plan, arranging rescue crew, 
supplying relief material, protecting people safe and so on. 
(3) . After flooding 
During the phase, UDSS supported by 4D and relevant 
technologies focus on the following tasks: 
• Evaluating flood damage 
• Planning and reconstructing project of preventing flood 
• Creating loss database of an insurance and paying 
insurance compensation 
4D products and associated enabling technologies provide