Tong Xiaohua

Probability density function and estimation for error of digitized map coordinates in GIS

Traditionally, it is widely accepted that measurement error usually obeys the normal distribution. However, in this paper a new idea is proposed that the error in digitized data which is a major derived data source in GIS does not obey the normal distribution but the p-norm distribution with a determinate parameter. Assuming that the error is random and has the same statistical properties, the probability density function of the normal distribution, Laplace distribution and p-norm distribution are derived based on the arithmetic mean axiom, median axiom and p-median axiom, which means that the normal distribution is only one of these distributions but not the least one. Based on this idea, distribution fitness tests such as Skewness and Kurtosis coefficient test, Pearson chi-square x2 test and Kolmogorov test for digitized data are conducted. The results show that the error in map digitization obeys the p-norm distribution whose parameter is close to 1.60. A least p-norm estimation and the least square estimation of digitized data are further analyzed, showing that the least p-norm adjustment is better than the least square adjustment for digitized data processing in GIS.

A WebGIS Based General Framework of Information Management and Aided Decision Making System for Earthquake Disaster Reduction

This article describes a methodology for establishing a general framework of the information management and aided decision making system for earthquake disaster reduction by means of a WebGIS. The system has a three-tier architecture consisting of data service, middleware, and expression service tiers. The system database is composed of the seismogeological database, the engineering environmental database, the disaster relief resource database and the analysis result database. The function components in the middleware tier include the earthquake hazard analysis, the construction vulnerability estimation, the quantifying economic losses and casualties caused by earthquakes, and the aided decision making components for post-earthquake emergency response. In order to further analyze earthquake damage data, three WebGIS analysis modules are designed on the client side, namely the foundational information module, the earthquake loss module and the emergency response module. In the information system based on this framework, the information about earthquake disaster reduction can be shared, the earthquake disaster data can be all-around analyzed, and aided decision making for post-earthquake emergency response can be efficiently made.

GML and XQuery based cadastral spatial object query model description and implementation

Taking cadastral feature as example, the spatial object query models based on GML and XQuery are proposed. The cadastral spatial feature models based on GML are first defined. The query models of the cadastral spatial objects are then presented. The topology relationships between these objects are derived. The relation query methods and algorithms between two objects are given in detail. A GML-based cadastral GIS system is further developed based on JAVA, DOM and SAX. The proposed spatial models based on GML and the query technologies based on XQuery are tested through the system, and the results show that it is feasible to implement XQuery to query the relationships between cadastral spatial objects based on GML.

A new least squares method based line generalization in GIS

The generalization of line features is an important process in both traditional cartography and in many applications of geographic information systems. In this paper, the parcel boundary line generalization is further studied. The uncertainties in Douglas-Peucker based line generalization algorithm is first analyzed, a line-fitting based line generalization algorithm is then proposed. In the new line generalization method, kinds of conditional equations in map generalization are therefore derived, including the length conditional equation, area conditional equation, and end-vertexes identical equation. Based on the theoretical discussion, a parcel boundary line generalization system is developed. The case studies are carried out to test the methods. The results show that the proposed uncertainty-processing model is feasible to ensure the data quality in map generalization