Cả tài nguyên khoáng sản lẫn các sản phẩm của sinh quyển được sử dụng để cung cấp cho cuộc sống của con người. Dân cư được chia thành hơn 200 quốc gia độc lập, có quan hệ với nhau thông qua các hoạt động ngoại giao, du lịch, thương mại, quân sự. | Virtual Environments for Geospatial Applications Figure 8. a 3D virtual environment depicting geospatial processes 1 picture of a series such as landscape change over time etc. b 3D virtual environment depicting water flow in a reservoir Critical Issues in the Design and Implementation of Geospatial Virtual environments This section concisely discusses some limitations and constraints typically experienced in several virtual world generations as well. One noteworthy issue is that in visualizing real-world scenarios there is an inevitable trade-off amid performance and resolution. Exploiting the complete capabilities of virtual environments over the Web continues to pose problems. As the number of objects in a virtual environment increases online hosting becomes an issue as spontaneous rendering of numerous objects is no easy task. Scenes with a greater number of polygons decelerate the system and make the interactivity poor. Several factors need to be considered during visualization such as the type and volume of data to be visualized memory constraints and system performance. Table 2 presents a summary of the significant issues concerning geo-virtual environments. In their work on information visualization Robertson et al. 1993 have presented a terse compilation of the important issues. In his work on dynamic and interactive webbased visualizations Huang and Lin 1999 2001 and 2002 discuss in detail some ofthese concerns and also address some critical issues concerning online hosting of interactive visualizations. The Java-3D based hybrid method that Huang and Lin 1999 2001 propose offers a standard framework Table 2. A summary of critical issues in designing and implementing 3D virtual worlds Photo-realistic scene generations Generating 3D virtual e nvironments with adequate photo-realism Bandwidth Limitations 3D Scenes with numerous objects rendering difficulty and transmission speed Browser and Plug-in Compatibility Compatibility among various browsers as well .
