Research On DEM Quadrianglated Irregular Network Modeling Method

Since 1958, Miller and LaFlamme firstly proposed the concept of digital terrain model (DTM), more concepts using digital technology to solve the same problems have emerged one after another. As one of the most representative, DEM is a finite sequence of three-dimensional vectors on region, and is an expression of the Earth's topography in discrete digitals. After several decades of development, DEM has become an important part of spatial information systems and provided data support in detection of the earth, construction and battlefield environment simulation.With the development of spatial information technology, significant changes have happened on DEM data acquisition, using satellites, radar interferometry and other techniques for rapid and efficient access to high-precision topographic data. However, purpose and cost factors are always taken into account firstly in practical applications. Engineering staff often choose a more effective and cheaper way of data acquisition such as data from original digitized topographic maps or photogrammetry. The data obtained in this way is essentially a discrete distribution of elevation points along the topographic features. There are four primary DEM models:point-based model, trianglated irregular network (TIN) data model, regular-grid data model and the way any two mixed. The most popular are TIN and Grid. TIN may contain more surface-specific points in high relief areas, such as peaks, pits, saddle points and points along streams and ridges. TIN also has the advantages of multi-resolution and high accuracy, but the complex topology limits its application in digital terrain analysis, especially in small scale environment. The advantages of regular-grid data model include the simplicity of the data structure, case of computation for surface analysis and smaller data storage capacity, but a large amount of data redundancy occurs in gentle terrain and the expression of high-relief are not fine. In this thesis, we hope to find a new DEM modeling method, including high accuracy of TIN and simple topology that simplifies terrain analysis algorithms.This thesis proposed the concept of quadranglated irregular network (QIN) to establish the relationship of discrete elevation points. With this concept, all original sample elevation points will be taken into account, points close to horizontal and vertical angles in plane will be distributed into one vector. By interpolating new points, a ultimately elevation matrix will be built.As basis of data structure, DEM model determines the specificity of related methods. This thesis proposes the generation algorithm of QIN and discusses the series of concepts related with DEM, including:(1)Raster and vector methods were used to approach contour extraction based on QIN. Raster method is more efficient is due to matching the topology structure of QIN.(2)In DEM editing, this thesis discussed a simple method about point feature adding and removing.(3)In data organization and management, file system is employed by small volume data. For large-scale data applications, database is adapted to management. It is necessary to reduce data storage by data compression, which ensures accuracy of data in certain case.(4)As the data basis of digital terrain analysis (DTA), DEM modeling has important influence on accuracy and algorithm efficiency of DTA. In this thesis, the extraction algorithms on basic DTA factors are discussed, including algorithms on slope and aspect, area and volume computing method and slope variability.Finally, DEM accuracy of the three modeling methods are evaluated and compared by two experimental areas. By compare several DEM accuracy factors, this thesis concludes that: QIN performed better than regular grid but slightly bad than TIN on accuracy; the average slope of QIN is much closer to the actual value than TIN and regular-grid. Although the accuracy of QIN is not the best of all DEM models, considering the characteristic of simple topology, simplicity and higher accuracy on DTA, it can be served as another good choice for DEM modeling.