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The surface of an airport project is a three-dimensional surface whose three-dimensional configuration has a very important impact on the complexity and user friendliness of the airport design. The traditional multi-fold surface is a kind of continuous surface connected by several triangular or rectangular planes. In order to solve the problem of the threedimensional shape of the airport engineering surface and to overcome the shortcomings that traditional multi-fold surface method cannot match the actual shape of the ground, a three-dimensional continuous warped surface model as the surface model of the engineering design site is used. The 3D geometric model is based on the central axis of the site as the longitudinal design control line, and this control line is used as the base line to expand to both sides of the center line. Each cross-section along the central axis is selected as the transverse design control line of the site surface. The design surface of the site between the transverse design control lines is warped surface. By setting the slope control parameters of individual warped surface, the three-dimensional shape of individual warped surface can be controlled as flat or warped surface. Using the longitudinal and transverse slope and slope section length of the geometric model, the design elevation expressions of the four corner points of the surface at any point k in the airport are derived, and then the design elevation of each net point on the four sides of the surface is calculated; the 2-dimensional 1-net function is used to establish the expressions of the design elevation of the surface, and the design elevation value of any point k in the surface is calculated. The error of the design elevation at point k is analyzed by using the principle of error analysis of the net function, and the calculated results in this difference are more accurate. In accordance with this design theory and design principle, corresponding calculation programs and drafting software were developed to relate the airport design 3D surface to the original 3D terrain around the field and to colour the operations according to the elevation, which creates a comprehensive airport terrain 3D design CAD system. The application of the curved surface as the airport design surface allows the airport surface to match the natural ground more closely and the net function to be calculated easily. The geometric model and its net function expression was applied to the design of Tianzhu Airport, saving 6.34% in earthwork volume compared to the traditional multi-fold surface method.
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