Brief Discussion of Surveying Technology of Three-dimensional Digital Topographic Map

3D digital Topographic drawing adopts 3D profile technology and demonstrates geographic space phenomenon to users, reflects the space features of geographic entity in an integrated and accurate manner and thus realizes even more complete, accurate and straight-forward expression of the objective world. It can not only express the plane relationship between space objects, but also accurately describe and express the ground elevation and geometric object height which upgrade the space expression ability and measuring level of digital map and enhance the space acknowledge ability and analytic ability of map. This article aims to elaborate on 3D digital topographic drawing in three aspects: surveying, mapping and application; mainly introduce the mapping methods of 3D topography and geometric object, integrated matching technologies of topographic model and geometric object model and application of 3D digital topographic drawing. It is expected to have a positive promotion role in the development of 3D GIS.