A 3D spatial data model is the foundation of 3D spatial database and 3D GIS

so it has great significance of research. A 3D spatial data model based on the 3D discrete domain

3D-realms

is introduced in this paper. It is the extension of the 2D realms in the 3D space. The basic definition

semantic description and the spatial operations of this spatial model are presented in this paper. This 3D spatial data model can be divided into four layers: 3D geometric primitives layer

3D-realms layer

basic spatial constructional elements layer and basic spatial objects layer which includes points object

lines object

regions object and bodies object. Each lower layer is the foundation of construction elements of the higher layer and provides supports for it. The 3D spatial data model based on 3D-realms can guarantee the correctness of topological relations

describe 3D spatial objects well and effectively support the 3D spatial topological operations.