Chongjun Yang

Visualization of large spatial data in networking environments

Rendering and interacting with high-resolution geographical data sets and complex models have become integral parts in a 3D GIS, in particular, in a web-based 3D GIS. Due to large data sets and narrow network bandwidth, general-purpose GIS can no longer visualize and manipulate these spatial data over networks in real time. This paper explores a way for building a Web-based 3D GIS application. The application aims to visualize and analyze large spatial data sets. We propose a novel 3D data model for representing the features of the terrain surface and 3D objects. A server-client architecture including progressive transmission methods and multiresolution representations are presented to help create the application. Together with a spatial index, the application provides an effective way for powerful access and manipulation of large-scale data sets. Finally, an experiment is performed using the geo-data to verify that the application works appropriately.

Research on mobile GIS based on LBS

Mobile computing system based on personal digital assistant (PDA) products has been used widely, and location-based service (LBS) is one of the most promising application directions of GIS. It is important to integrate the mobile computing technology and GIS technology to meet the need of LBS. The purpose of the paper is to propose a solution of mobile GIS based on LBS by studying the difference between the personal digital assistant (PDA) and traditional desktop computer. The totally new system architecture of the system and detailed function of each component is presented, and on the base of this, the method of spatial data management, spatial data compression, spatial data index, and the visualization of digital maps are also proposed. Base on our strategy, a GPS device is used to get the location information to prove the validity of our strategy. Experimental results demonstrate our strategy can meet the actual need of enjoying LBS anytime and anywhere.

An effective buffer generation method in GIS

Buffer Analysis is one of the most important functions of spatial analysis in GIS. This paper uses rotation transform point formula and recursion method to further improve on the vector buffer generation algorithm of double parallel lines and circular arcs, simplifies the process of the generation of parallel lines and the circular correction of sharp angles, and finds a better solution to intersection problem of borderlines of buffer zone.

A load balance algorithm for WMS [Web Map Service]

Web Map Service (WMS) provides spatial information to Internet users by map images. Commonly, spatial data are stored as vector data. It is a long job to create map images from vector data. To reduce the time cost, we employ Linux cluster. When a map is requested, coordinates scope that is a rectangle defined with xmin, ymin, xmax, ymax must be specified. We design a load balance algorithm to divide the request rectangles into some sub-rectangles. Each sub-rectangle is sent to a WMS node to produce some sub-maps. The resulting map will be reconstructed by these sub-maps. All these sub-maps are produced in parallel, so less time is spent in producing an entire map. How to split request rectangles is the key problem. First, we present a method to calculate the 2D load weights distribution in the map scope. Second, nodes load abilities are evaluated. Then, the authors present a method for splitting the entire rectangles. This paper also discusses the performance of the algorithm.

OpenGIS WMS-based prototype system of Spatial Information Search Engine

Spatial Information Search Engine (SISE), aiming to search the World Wide Web for online geographic information to meet the end users needs, is a totally new research area in the field of spatial information sharing. In this paper we introduce an OpenGIS WMS specification based SISE prototype system. This SISE prototype is capable of discovering available WMS servers dynamically, choosing qualified WMS servers according to the client request, and fetching the matched geographical information from them transparently. The system architecture, working principles, detailed function of each component, implementation strategies and system performance test results of this SISE prototype are introduced.

A web-mapping system for real-time visualization of the global terrain

In this paper, we mainly present a web-based 3D global terrain visualization application that provides more powerful transmission and visualization of global multiresolution data sets across networks. A client/server architecture is put forward. The paper also reports various relevant research work, such as efficient data compression methods to reduce the physical size of these data sets and accelerate network delivery, streaming transmission for progressively downloading data, and real-time multiresolution terrain surface visualization with a high visual quality by M-band wavelet transforms and a hierarchical triangulation technique. Finally, an experiment is performed using different levels of detailed data to verify that the system works appropriately.

Effective techniques for interactive rendering of global terrain surfaces

Global terrain visual systems must support real-time visualization and manipulation of huge multiresolution geographical datasets. In this letter, we focus on certain key techniques, such as construction of three-dimensional (3-D) ellipsoidal models, spatial indexing mechanisms, interactive terrain datasets simplification by the M-band wavelets and triangulation techniques, and surface browsing from different view directions. Finally, an experiment is carried out using different levels of detail data; our results suggest that the methods are effective in enhancing performance of a 3-D global visual system.

A WebGIS for sharing and integration of multi-source heterogeneous spatial data

Data sharing and integration are the inherent request of GIS. Data format conversion, data interoperability and direct data access are three ways of data sharing. All of them have many shortcomings respectively. So this paper proposed a method to build a WebGIS for sharing and integration of multi-source heterogeneous spatial data well. It introduced different data of multi-formats and several spatial database engines into a data access layer which established a unified data structure for screening the difference of different spatial data, and distributed spatial data using the GML, WMS and WFS standards developed by the OGC. Through those ways, it made heterogeneous spatial data homogeneous and enabled different data to have the unified and transparent structure to all users. The results show that the system share and integrate multi-source heterogeneous spatial effectively.

Application of M-band wavelet theory to texture analysis in content-based aerial image retrieval

With the rapid development of 3S technologies, content-based retrieval from remote sensing images provides an important means of information acquisition and sharing and has become a key technology in digital earth construction. This paper puts the emphasis on using texture features for retrieval of aerial image database. M-band wavelet theory is introduced and M-band wavelet histogram technology is applied to texture extraction. Some experimental results are given to evaluate the retrieval performance of our method and to compare with that of method based on traditional two-band wavelet transform, followed by conclusions

A prototype system of content-based retrieval of remote sensing images

The problem of content-based retrieval of remote sensing images presents a major challenge not only because of the surprisingly increasing volume of images acquired from a wide range of sensors but also because of the complexity of images themselves. In this paper, a prototype software system for content-based retrieval of remote sensing images, namely CBRRSI, is introduced. The main contribution of our research work is the novel wavelet-based feature representation approach and the flexible progressive retrieval strategies based on multi-descriptors. Some experimental results are given to prove the validity of the CBRRSI.