shows the arrangement of the screens. Each screen is 70 inch wide. The total view angle with the five screens is 225 . The observer in front of the screens is able to have a real time image of high waves and tsunami propagation in the field. The presented graphic images can expressed as 'virtual reality image'.
Figure 1 Arrangement of screen
For the expression of tsunami propagation, the background like houses, mountains and port facilities should be kept in the computer hard disk in advance. The software 'MultiGen' by Software System Co. are applied to complete the background image data. The photographs of buildings and houses are able to be overlapped on the image data on the screen. The software 'IRIS Performer' by Silicon Graphics Co. are employed to form the three dimensional graphics of the tsunami attack and background. This system has the following functions;
(i)Data Curling Function:The graphic image data beyond the view angle is not calculated to reduce the CPU time.
(｢)Level of Detail Function The detail level of graphic image is changed according to the distance of the object from the observer.
In the tsunami simulation, the water level and flow velocity in the two components are output at each time step. For wave transformation, the valiation of water levels at each computation point and time step are memorized in the system hard disk.
For the computer graphics of three dimensional objects, the following three models are available;
(i) Wire Frame model A three dimensional object is expressed in wires (line). The memory size necessary to the model is the smallest, so the high speed graphic is available.
(｢) Surface model: A plate is set on the space surrounded by wires in the wire frame model. In this model, a large number of two dimensional planes are employed to express the three dimensional figure. The plane is called 'Polygon'.
(｣) Solid model: The internal information of an object is added on the plane in the Surface model.
For the wave and tsunami propagation graphic, the surface model is employed. Figure 2 shows the arrangement of computation grids. The computed water surface elevation is given on the corresponding grid. The value of -99m is allocated to the grid in the land as dummy. The vertical wall may be formed on the sea-land boundary without any modification. To protect the formation of vertical walls, we give an averaged water level to the land grid one mesh inside of the boundary. The averaged water level is calculated employing the water levels on the surrounding grids. The moving boundary of shore line is computed as the cross line of the sea polygons and the land polygons. The height data of land is derived from the 'Numerical Map (250m mesh)' published by the Geographical Survey Institute, Ministry of Construction.
3. GRAPHICS IMAGE OF TSUNAMI INVASION
(1)Simulation Model
In the tsunami simulation, the initial distribution of
