Guo Qingsheng

Construction of E-Government GIS Based on Net Platform and Web Service

Based on the characters of the E-government GIS, the advantages of the E-government GIS construction based on .Net and Web Service are analyzed. Based on this, the general framework of this system is designed, and a new model of publication prototype of spatial information is put forward , and the technical scheme about client, server and database are implemented. Finally, the application of the system is introduced.

A Progressive Line Simplification Algorithm

An application of line simplification considering spatial knowledge is described. A method for identifying potential conflict regions, in order to avoid the self-intersection of generalized, lines, is also discussed. Further-more, a new progressive line simplification algorithm is presented. From the view point of spatial cognition, a spatial hierarchical structure is proposed, and its application to construction of spatial knowledge related to a line is explained.

Research on fractal characteristics of urban traffic network structure based on gis

Traffic network is an importance aspect of researching controllable parameters of an urban spatial morphology. Based on GIS, traffic network structure complexity can be understood by using fractal geometry in which the length-radius dimension describes change of network density, and ramification-radius dimension describes complexity and accessibility of urban network. It is propitious to analyze urban traffic network and to understand dynamic change process of traffic network using expanding fractal-dimension quantification. Meanwhile the length-radius dimension and ramification-radius dimension could be regard as reference factor of quantitative describing urban traffic network.

Measurement of similarity for spatial directions between areal objects

Similarity for spatial directions plays an important role in GIS. In this paper, the conventional approaches are analyzed. Based on raster data areal objects, the authors propose two new methods for measuring similarity among spatial directions. One is to measure the similarity among spatial directions based on the features of raster data and the changes of distances between spatial objects, the other is to measure the similarity among spatial directions according to the variation of each raster cell centroid angle. The two methods overcome the complexity of measuring similarity among spatial directions with direction matrix model and solve the limitation of small changes in direction. The two methods are simple and have broader applicability.

Progressive graphic simplification of contours based on spatial reasoning

This paper discusses the rules representing relief with contour lines and methods for automatically constructing relation of contour lines. Mean-while, the improvement of existent methods for extracting the topographic characteristic points and lines is described. On the basis of this analysis, we propose a series of practicable progressive graphic simplification ideas of contour lines and concrete algorithms for the exception’s handling. In this way, graphic generalizations of contour lines at different scales are integrated into one model that is convenient to implement, and in which contour lines’ intersection in generalization can be controlled.

Research on discrete points of electric field model for conflict detection and displacement

Conflict detection and displacement are significant operators to maintain spatial relationship of map elements in cartography. At present, much attention has been paid to element division for local conflict detection and progressive displacement. By deeply observation, analysis and experiment, many models have been found good applicability for cartography, such as structure mechanics model, snake model, delaunay model, et al. But local conflict detection and progressive displacement still need more researches to achieve automatic cartographic generalization. In this paper, electric field model is proposed firstly to try conflict detection and displacement. Distribution of electric field is suit for conflict detection and displacement of map elements, since conflict occurs in local and changes with range. The main idea is to take conflict of road and building elements as that of points scattered from lines, and points represent particles with electric power. Conflict can be expressed by electric repulsion between particles. On the basis of electric field model, an algorithm and workflow is designed to verify the model effectiveness. The experiment concludes that the quantitative relationship of scale factor to discretization step and displacement amount is credible, and progressive displacement algorithm is effective for conflict detection and displacement.

The spatial characteristics of a line and their application to line simplification

This paper discusses the spatial knowledge related to a line, and the characteristic points of lines is detected. According to the requirements of line generalization, new algorithms for identifying characteristic line points are presented. These characteristic points are used to improve the algorithms of line generalization. An algorithm for identifying bends is shown. In this paper, improved algorithms based on those by Douglas-Peucker, Visvalingam and Whyatt are shown. In this test, the progressive process of line generalization is emphasized.

Computational complexity of spatial reasoning with directional relationship

The property of NP-completeness of topologic spatial reasoning problem has been proved. According to the similarity of uncertainty with topologic spatial reasoning, the problem of directional spatial reasoning should be also an NP-complete problem. The proof for the property of NP-completeness in directional spatial reasoning problem is based on two important transformations. After these transformations, a spatial configuration has been constructed based on directional constraints, and the property of NP-completeness in directional spatial reasoning has been proved with the help of the consistency of the constraints in the configuration.

The method of graphic simplification of area feature boundary with right angles

Some rules of simplification of area feature boundary and the method of acquiring spatial knowledge, such as maintaining area and shape of area feature, are discussed. This paper focuses on the progressive method of graphic simplification of area feature boundary with right angles based on its characteristics.