GIS-based Visualization System Of Tide And Tidal Current Trends

We have predicted tide and tidal for hundreds of years. But the previous data of tide and tidal was obtained from tidal wave equation by numerical calculation, and it was abstractive, insipid and unreadable. In recent years, people focus on how to convert these boring data to the one which can be understood easily, intuitively and vividly. So that the visualization techniques can not only describe the motion law of the tide and tidal current but also make people learn more about the variation of the tide and tidal current.In this paper we analyzed and designed the structure and function of the system by using Unified Modeling Language (UML), and introduced the development environment and platform briefly. In order to make the system easily managed, we regulated the storage format and installed the data and application program in the same path. After analyzing the tide and tidal data, we made out the limit of data query. Besides, we also described the distribution and processing of tide and tidal in this paper.On the condition of the limit of data query, we can read the data by the data I/O function of the system. There are two types of data of the tide and tidal, the distribution data and the processing data. And each of them needs the different function to read it. All these functions were packaged in CTC class.The key techniques of visualization to the tide and tidal is mainly about the visualization of the tidal data. The tidal data is expressed by vector with length and direction. The tidal power can be measured by the length of the vector. There may be a problem that the differences of tidal power when it is very large in a big area. Thus, we make mean value to the tidal data of the selected area to ascertain the length of the vector. If the vector was designed to be too short, the movement of the tide and tidal will be inconspicuous. On the other hand, if it was designed too long, it will overstep the grid and look disordered. For the above reason, we must choose the appropriate length.The tide and tidal data was read by Visual C++6.0. After being read the geographic coordinate was converted into screen coordinate using the mapping function so that the graph was showed beautifully. The current trends displayed showed the motion state of the tidal and described the tidal data of a period of time. Thus, it will be presented vividly for the tidal motion state.To check the accuracy of visualization to the tide and tidal data, the tidal observatory data obtained from Xiamen, Chongwu and Pingtan observatory station, are applied from January to September in 2007. However, the difference between the measured data and prediction data is only several centimeters, which can completely meet the requirement.