IV. EXPERIMENTS AND ANALYSIS
Based on the principles above, the 3D map symbol library
is built in 3D large-scale environment and the 3D symbolic
database system is developed which is suitable for geographic
features to be symbolized in a large area of terrain
preliminarily. In Windows environment, the example of 3D
geographic information symbolic display are finished by using VC programming language combined with OpenGL graphics
library. From experiments, it proves that 3D symbols have a
very good visual effect on presentation of geographical
features, and it plays a significant role for enhancing map
expression and the user's cognitive level of geographic
information. Figures 2~4 show the effects of related
experiments