Based on the theory of map information transmission, the
categorical rule and drafting law are researched and a principle
of establishing a 3D symbol is presented in this paper, which
contains two aspects The one is that all kinds of spatial feature
information which are suitable for description by 3D symbol
models have been identified, the other is that it should be
implemented at the viewpoint of computer graphics and
visualization. And the basic concept of 3D map symbol model
and the relation between traditional 2D symbol and 3D map
symbol are stated, which include (1) 3D symbol is not to deny or
abort using 2D symbols, but to complement and enhance 2D
symbols; (2) 3D symbol enriches and augments the way of map
representation, promotes the study on the latest 3D area of
cartography, and acts as critical role on research and
development of new map visual products. Meanwhile, a principle
of generating a 3D symbol is also proposed, which are (1)
description in abstraction and visualization; (2) logicality; (3)
conciseness; (4) feasibility. The research in this paper lays theory
fundament for establishment and applications of 3D symbol
database. In addition, the approach and basic procedure of 3D
symbol modeling is given in detail which consists of 3D entities
modeling, symbol render and assignment processing, scenery
conflating of 2D symbol and DEM, symbol algorithm design, etc.
The technology of texture gradational blending is adopted to deal
with the crack of rendering line symbols and area symbols caused
by boundary transition, which can implement the boundary
mutation on the condition of texture rendering of line and area
symbols and realize a perfect visual effect. And the boundary
model(BR), parameter model and construction entity
geometry(CSG) method are integrated to represent the symbol
spatial information in design an entity model, which finishes the
structure design of symbol figure information.