Three dimensional terrain is one of important factors of the natural scenes in virtual environment. It is also a significant composition of view system in virtual simulation field. The paper presents terrain generation techniques based on real terrain datasets

and terrain simulation techniques that are based on fractal geometry as well as data fitting methods respectively. Among the terrain generation techniques based on real terrain datasets

emphasis is laid on the real-time display of terrain and some typical data simplification algorithms are introduced according to their appearing time: discrete LOD

continuous LOD

and multiresolution model. Related conceptions and features of those algorithms are also discussed. In terrain simulation techniques based on fractal geometry

the paper gives an overview of several fractal modeling methods

and then makes a further discussion on two kinds of typical recursive subdivision plans of midpoint displacement that is the most practical approach in some applications. In data fitting techniques

plane fitting

curved surface fitting

and real terrain simulation according to some given topographic parameters are introduced. Finally

the development tendencies of all these techniques are discussed.