In a large three-dimensional Geographic Information System （GIS）

we usually reconstruct a triangular network on the local terrain on the basis of the complete preloaded terrain data for some specific applications such as a physical engine. In order to handle this problem

we propose a real-time algorithm for local three-dimensional terrain simplification

by using up and down sampling and the pyramid theory. This algorithm executes the down sampling and the up sampling at the triangle grid of the original terrain

then performs the partial revision with the predicted residuals in specific regions

and finally obtains the fine terrain triangular network

which is considerably similar to the original terrain. We have applied this algorithm to the simulation of a vehicle driving application in our GeoBeans three dimensional system. The terrain constructed by this algorithm is simplified and stable. It will be updated according to the range of the vehicle and be destroyed or reconstructed as needed. Our test shows that if the threshold of the predicted residuals is 0. 1

the number of triangles will reduce to 2/3 of the original number; if the threshold is 0.2

the number of triangles can almost reduce to 1/4. Hence

as demonstrated here

in the visual precision permitted range

this algorithm results in a good terrain simplification with little time consumption

and it satisfies the request of real-time simplification for a three-dimensional system and the simulation of a vehicle driving application.