It is a period of explosibility information. Especially for spatial information science, information can be acquired through many routes, such as man-made planet, aeroplane, laser, digital photogrammetry and so on. Spatial data sources are usually distributed and heterogeneous. In order to share and interoperate spatial data, federated database is the best resolution. In this paper, the concepts of federated database and interoperability are introduced. Three heterogeneous kinds of spatial data, vector, image and DEM are used to create integrated database. A data model of federated spatial databases is given.

This paper describes a series of tests on the accuracy of DEMs. The effects of 4 factors on DEM accuracy have been tested, i.e. the accuracy, density of source data, the characteristics of terrain surface and the modelling approaches. A large area covered by two 1:10,000 maps were selected for testing. The terrain types range from flat, hilly to mountainous. Various sources (photographs and contour maps) are used and measurement methods employed. From test results, the followings have been found: (a) Source data measured manually from analytical plotters is most reliable as automated measurement using image matching could generate systematic errors; (b) The accuracy of DEMs decreases (or RMSE becomes larger) with an increase in sampling interval and the relationship is linear; (c) The inclusion of feature points and lines improves the accuracy of DEMs significantly, especially when the terrain is rough; (d) Generally speaking, the accuracy of DEMs decreases with an increase in relief, however, it is not always the case and the best results may be obtained in hilly areas; (e) The direct modelling from originally measured data to form triangular network will yield better results than the indirect modelling via a random-to-grid interpolation to form grid network. The difference could be significant if the terrain is rough. From these conclusions, some advice on DEM production could be made as follows: (a) When using automated photogrammetric system for data acquisition, editing by experienced operators should be considered; (b) In hilly areas, photogrammetric contouring can be most efficient methods for DEM data acquisition if analytical plotters are used; (c) Feature points should always be measured and kept in order to reduce the data volume while retaining the fidelity of the DEM; and (d) When terrain surface is rough, triangulation-based methods are recommended.

数字地球作为一个战略目标在我国已被广泛接受，与此相关的数字中国、数字省、数字城市等工程正在全国如火如荼地展开。什么样的系统适应于构造数字地球、数字中国、数字省、数字城市的基础平台呢？从数字地球的基本构成、特点和当前技术的发展状况来分析和介绍适应于构建数字地球的新一代GIS软件的设计与实现。

新一代地理信息系统要求矢量、影像和DEM数据集成化管理。本文提出了一种基于面向对象思想的矢量、影像和DEM三库集成的空间数据模型，讨论了集成化空间数据库管理系统的实现方式。该空间数据库管理系统已作为GIS软件GeoStar的核心，被用于中国的空间数据基础设施建设，管理国家级、省级和市级的多数据源、多比例尺的空间数据，被认为是一种高效可行的方案。

With the increasing maturity of distributed object technology,CORBA,.NET and EJB are universally used in traditional IT field. However, theories and practices of distributed spatial database need farther improvement in virtue of contradictions between large scale spatial data and limited network bandwidth or between transitory session and long transaction processing. Differences and trends among of CORBA,.NET and EJB are discussed in details, afterwards the concept, architecture and characteristic of distributed large-scale seamless spatial database system based on J2EE is provided, which contains GIS client application, web server, GIS application server and spatial data server. Moreover the design and implementation of components of GIS client application based on JavaBeans, the GIS engine based on servlet, the GIS Application server based on GIS enterprise JavaBeans(contains session bean and entity bean) are explained.Besides, the experiments of relation of spatial data and response time under different conditions are conducted, which proves that distributed spatial database system based on J2EE can be used to manage, distribute and share large scale spatial data on Internet. Lastly, a distributed large-scale seamless image database based on Internet is presented.