Terrain visualization is playing a key role in many scopes such as geographic information system, visual reality, simulation system and 3D games, etc. With the lodged of Digital Earth plans, large-scale terrain visualizing becomes the research hotspot of the scholars all over the world.This thesis studies the key technologies of terrain visualization, improves the algorithm of LOD, constructs a view-dependent continuous multi-resolution terrain model, and implements a large-scale terrain visualizing and roaming system. First, the thesis uses the quadtree structure managing the terrain data from the characteristic of the regular square grid, to enhance the speed of terrain model generation and node visit. Second, it constructs a node evaluating function based on camera position and terrain’s roughness, in order to integrate the hypsography information into the model, and improve the render effect of the detail characteristic. Finally, it implements a crack eliminating algorithm to eliminate the cracks generated with using the quadtree structure, through adding or deleting edges at where the details changed. The thesis also adds visibility eliminating algorithm and reality increasing technology into the demo system to boost up the rendering speed and effect.Using OpenGL, the thesis implements a terrain visualizing and roaming system, and tests it with the larger-scale terrain data sets from USGS on PC platform. The average rendering rate is up to 30 fps, and the rendering result have more details, can satisfy the real-time request. Experimental results show that the view-dependent continuous multi-resolution terrain model is effective for the exploitation of large-scale terrain visualizing and roaming system.
What is GIS?
GIS is a computer system for capturing, storing, checking, integrating, manipulating, analysing and displaying data related to positions on the Earth's surface.
Research and Implement of Large-Scale Terrain Model Visualization Technology
The Change of Landscape Patterns and Its Effects on Soil and Water Loss in the Important Water Source Region-Dongzhen Reservior Shed Area
The per capita water resource of China which has large population is low. The phenomenon of water quality pollution and soil and water loss are poor. In water shed area, unreasonable land utilization and the development of mountainous region affected the overall regional pattern of the regional landscape. The changing of the landscape pattern not only created serious soil erosion moreover aggravated the formation of the non-point source pollution. Therefore, from the aspect of landscape, exploring the soil and water loss influence caused by different landscape patterns and combined the soil and water loss with landscape is an important subject in soil and water loss and landscape ecology. Taking the area of Dong Zhen Watershed as the research background, according to the observation on field and the application of spatial analysis, mathematical statistic, landscape structure analysis, the article analyzed the space and time variation patterns of the land utilization and the space and time relationships with the terrain factors. Then based on this, we use the USLE model to simulate how different land utilization patterns influent the soil erosion.The conclusions included: the overall landscape multiple indices increasing in the research area, the cultivated land reducing obvious and the forest land increasing obvious in the great slope area, so the whole of the land utilization structure tends to be reasonable. The area of the soil erosion which is above the mildly level trends to reduce gradually and the soil erosion intensity transforms to the lower level from 1995 to 2007 in the research area. Indicated that along with the Implementation of reservoir Returning farmland to forest project, construction of the ecological protection measure, east the soil erosion of Dong Zhen Watershed was distinctly improved, the ecological environment obtained the restoration gradually.
Research on Spatial Data Visualization of WebGIS Based on SVG
The informationization of society and development of network technology provide widest space for WebGIS to popular. Traditional Web language HTML is a kind of hypertext markup language. With the appearance of manifold information type, the disadvantages of HTML for representing spatial data are exposured. Many applications of WebGIS are based on special GIS software, but the software and the data format are various, it’s hard to interoperate and lack of agility.The researchful actuality, the realized method, the common structure model of WebGIS are analysed in the paper and the developing trend of webGIS is summed up.The advantages of SVG are strengthened by researching the technologies of SVG. GML is used to solve the integration and interoperatility of multi-source spatial date and to complete transmission on the Internet. With many characteristics such as compatibility, dynamic,interoperatility,scability,independence, SVG can satisfy the increasing demands.Combining the GML and SVG is able to resolve the problems of WebGIS about the vector transmission and the spatial data displaying. GML is used as the exchanging data about multi-source spatial date on the client to complete exchanging and sharing the information. SVG is used as the format of vetor maps to complete the spatial data visualization. The model of WebGIS is built based on SVG.The research about the spatial data visualization on the client is emphasized with some key technologies which are discussed to make up the plateform. The theory that the format of spatial data is transformed from GML to SVG with XSLT is researched. The map will be loaded and transmitted by compress after completing transform to complete visualization.The structural model is validated by experiment at last to complete spatial data visualization. How to realize the performance optimized of WebGIS based on SVG is set forth at the end of the paper.
The Design and Implementation of Town Cadastral Management Information System Based on Geodatabase
Town cadastral management is the core business of the land management. Along with the deepening and development of economic reform, laws and regulations of land management continue to improve, the rapid development of urban construction, and land ownership changes have become very frequent. To build a powerful and efficient operation of town cadastral management information system is an important task for town cadastral management.Town cadastral database has an extremely important position in the town cadastral management information system, it is the key to town cadastral management information system function. In this paper, the use of ArcGIS Geodatabase data model design town cadastral database, Town cadastral database achieve spatial data and attribute data stored in the Oracle database in uniform. Make use of embedded GIS component library of ArcGIS Engine, In the Visual C# 2005 environment, author develop town cadastral management information system.In this paper, the results are as follows:(1) Study of the Geodatabase data model, the use of Geodatabase data model establishes the town cadastral database. Design for town cadastral database is as follows: hierarchical design, attribute table structure design, metadata design, topological rules design, as well as storage structure design.(2) In this paper, author develops town cadastral management information system. Functions are as follows: graphics editor, query parcel of land, changes of parcel of land, looking back in history of parcel of land, output of parcel of land map and so on.
Research on the Key Technologies in Raster Data Storage Management Based on Spatial Database
Along with the unceasing gain and popular use of raster data, the technology in raster data management has become one of the hotspots in GIS research. An feasible solution for managing mass raster data effectively is Spatial DBMS, which can be implemented in two modes:"Relational DBMS+Spatial Data Engine" and "Relational DBMS+spatial extension". The later one is closely combined to the kernel of DBMS, which take full advantage of the advanced technologies of Relational DBMS, so it has a wider future than the former, and it will represent the main direction of the Spatial DBMS’s development.We carried out a series of extensions and amendments based on the open source Relational DBMS—Ingres, and finally implemented a Spatial DBMS IngreSDB. The study of this paper focuses on the storage mechanism for raster data in IngreSDB, as well as the problem of memory management which arises when the storing of raster data is executed.On the aspect of raster data storage, we define a kind of Raster Data Model which supports the blocking storage pattern for raster data, as well as the physical storage model for raster data which allows users to chose DBMS or File System as the container of raster blocks. As a result, IngreSDB can implement the blocking storage pattern for raster data in two different manners:the "in-table" manner based on Raster Block Table and the "out-table" manner based on block files. In this paper, we describe the design idea of the two manners respectively, as well as the methods to realize them. At the same time, we draw a comparison between them about their performance and applicability.On the aspect of memory management, we adopt Memory Pool technology instead of the default memory management mechanism of OS, put forward a kind of memory management strategy based on Memory Pool, and apply it in the implementation of raster data storage. The result of the performance test shows that, this strategy can not only improve the storage efficiency of raster data effectively in IngreSDB, but also avoid memory leak. So it is a safe and efficient memory management strategy.
