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Topographic data obtained by an airplane-base survey is spatially disordered. There are a high density portion and a low portion in the topographic data, and some data is unnecessary. A graphical terrain model is generally generated from a raster data, and the decimation in data is performed using the data structure. However, it is not useful to rasterize the topographic data by a high accurate laser range finder because one of the obvious sources of visual and numerical errors is that introduced by raster data structure employed by a digital elevation model (D2EM). In this research, the topographic data was obtained by a one-axis laser range finder mounted on an unmanned helicopter. Therefore, the data positions were spatially random. This paper describes the methods that can automatically generate triangle polygons from the topographic data set, and simplify the data maintaining accuracy. As a result of evaluating topographical feature error with simplification of the data obtained by the helicopter-base survey, even if the data was reduced by 400 points, topographical error was less than 12 cm.