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The UrbanFloods Project
clock.jpg Nowadays, the precise 3D urban models with all buildings, roads and infrastructure including the electricity lines, water and gas pipes have been created and are available for several cities in the world. Much money has been paid to create and update such models but the open question remains how to use such expensive data. This project is focused on the research of methods that will enable the utilization of 3D city model in three topical areas, comprising the three main packages of the project:
"    urban planning (P1),
"    flood prevention (P2)
"    flora planning (P3).
We will make use of available and new mathematical models and computer graphics methods to develop utilities and applications able to process and visualize the urban data. Our applications will utilize during the research and also in the final version urban data of Bratislava city and Danube River but are not limited only to them. Bratislava has been chosen because there is the compact part of 3D virtual city model (the other cities in Slovakia are only starting in this field) available and also the digital data partially describing the riverbed of Danube. The state of art and contribution in the particular areas is as follows:

P1: Urban planning
Urban planning and urban action is provided by Act No. 50/1976 on the regional planning and construction order (the Construction Act) as amended by later provisions. Section 7 of the quoted Act provides the so called urban action, especially the decision making process on the localization of the buildings according to paragraph 32 of the law and the other paragraphs. The Act describes the necessary data for the urban action and the criteria for the decision of the legal authority. If the virtual 3D city model will be available, it can be used as the aid to decision making process, because it will enable the more realistic evaluation of the building localization from various aspects (the harmony with the existing building development, visibility, light and noise conditions etc.). This will be very useful in the public discussion foreseen by the law mainly in the case the sensitive constructions. The research will be focused on the utilization of existing and new methods of computer graphics and vision on the urban and terrain data (the visualization from the chosen perspective, visibility, models of light and noise distribution), including the modeling tools for embedding the new construction in the existing one. In Slovakia we are not aware of any product solving the computer support for urban planning utilizing the 3D city model. From the foreign products the commercial software system CityGrid from company Geodata [5] should be mentioned. It's part is also the CityGrid Planner, oriented on the support of urban planning [6].

P2: Flood Prevention
Animations and forecasts of floods are getting more and more popular nowadays. Slovakia belongs to countries with frequent flood disasters, remember flood in Bratislava in year 2002 caused by Danube or flood in 2004 at eastern Slovakia, which caused big damages on population and agriculture. Flood disasters worry the human civilization from the beginnings of its existence. Nowadays we are getting into phase, when we have sufficient computer hardware capabilities and knowledge to be able to simulate these natural phenomena. Under the term of simulation we mean calculation of water flow, deposition of clay and gravel, and afterwards their visualization. On the base of our product it will be possible to distribute water barriers and afterwards to test the changes in water flood. At this package we will propose also new techniques for fast simulation.
All the current methods for simulation of fluid dynamics are based on a physical model described by the Navier-Stokes equations that ensures conservation of mass and conservation of momentum while computing new velocity and pressure field. The first use of this computational fluid dynamics technique for computer graphics was Chen and da Vitoria Lobo [2] whose method used a relaxation method to solve 2D Navier-Stokes equations. Solving 3D Navier-Stokes equations was popularized in computer graphics by Foster and Metaxis. In a series of several papers they demonstrate how the Marker-And-Cell (MAC) approach of Harlow and Welchom [3] can be used to simulate water and smoke. A Volume-Of-Fluid  (VOF) method introduced one very important scalar value into the simulation process and it is the exact volume of fluid within the simulation cell and uses marker function. Since it holds only one scalar value, the volume of one fluid, it can not solve multiphase problems. This disadvantage is very effectively replaced by the multi fluid representation designed by Tomoaki Kunugi[1]. Visually pleasing animations can be achieved by using a particle level-set [4] method.

P3: Flora Planning
Garden planning is now a common technique when designing the building environment. When and architect needs to design a small garden he will select every single plant to be used but if we plan to design large green areas or alley we may prefer a semiautomatic generation of trees. If we could simulate the tree growth we can estimate how the garden will look like after several years and predict the consequences.
TODO
Again we will use the standard CG tools to distribute the trees automatically in the city then we let them grow and finally we visualize the situation in the city after several years. We can the estimate for example if a large tree will obscure the building or power lines.

[1]    Tomoaki Kunugi (Dept. of Nuclear Engineering, Kyoto University), MARS for Multiphase Calculation, February 10, 2000.
[2]    Chen, J. X. and Da Vitoria Lobo, N., Toward interactive-rate simulation of fluids with moving obstacles using Navier-Stokes equations, Graphical Models and Image Processing, Academic Press, Volume 57, Number 2, 107-116, Academic Press, Inc., 1995.
[3]    Harlow, F. H. and Welch, J. E., Numerical calculation of time-dependent viscous incompressible flow of fluid with free surface, Physics of Fluids, vol. 8, pp. 2182-2189, December 1965.
[4]    Foster, N and Fedkiw, R., Practical animation of liquids, Proceedings of ACM SIGGRAPH 2001, 23-30, ACM SIGGRAPH, August 2001.
[5]    www.geodata.at
[6]    http://213.229.30.43/documents_en/CityGrid.pdf
[7]     http://www.blender3d.com, open source multiplatform software for 3D modeling, May 2005
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