Abstract: Based on the topographic map of 3D modeling of AutoCAD platform, the accurate
calculation of 3D visualization design is very important in earthwork engineering at the present stage.
The general process of modeling 3D topographic map of a net surface is that a three-dimensional
entity is stretched into by using of 2D polyline or 3D polyline. In this process, there are 20%–25%
degradation of tensile objects, and it is needed to manually build triangle region, then these objects
extruded. This is serious impact on modeling speed. The “boundary” function is called to generate a
triangular irregular network area and then a sweep and lofting the interface function along the Z axis
of the triangular mesh surface domain stretching formation of the three-dimensional object using
coordinate transformation and contour data based on ObjectARX development technology. The fast
terrain modeling is realized.

Key words: AutoCAD, ObjectARX, boundary, solid modeling