| In2009, U.S. Environmental Systems Research Institute, Inc. proposed the concept of geographical design, trying to integrate GIS technology with CAD to combine geography with design, providing people with powerful mapping, data management, spatial analysis and display tools. However, the integration of GIS and CAD is undesirable, so the data sharing of which is generally done by direct conversion, but the after information and geometry deformation and layers don’t match the before ones. The reason lies in the complexity of geographical objects and geographical phenomenon and the differences of the view points, interests and methods of people, which making the description of GIS and CAD to the same geographical objects and geographical phenomena are not identical. Therefore data structure, organization form and space basis between the two platforms are different, which led to geospatial data sharing and interoperability difficult between the two platforms. Therefore, it is urgent to study the difference between the geospatial data model of the two platforms in order to solve the problems of geospatial data sharing, so that to achieve a unified geospatial data model and lay the foundation for cross-platform data interoperability.Basing on that, by taking the geospatial data model as object of study, based on the defects in the existing sharing methods, this paper compared the OGC standard, ISO specification and geospatial data models of common software, then present the cross-platform geospatial data model for sharing, established mapping relation between geospatial data model for sharing and ArcGIS, AutoCAD model. And based on geospatial data model for sharing, a data sharing method is proposed, the compatibility of geospatial data model for sharing, as well as the feasibility of the method is verified. The realized two-way data sharing between GIS and CAD could solve several problems in the existing sharing methods.The content and the results of this study are as follows:(1) The geospatial data model for sharing between GIS and CAD is presented. The geospatial data model of GIS and CAD is compared in seven aspects, which are their geometric primitives, the descriptive power of the data model, spatial references, calculability, compatibility, data organization and attribute data organization. On this basis, the geospatial data model for sharing to achieve the unified description of the geospatial data models of two platforms is built.(2) The method of two-way mapping between GIS and CAD geospatial data is put forward. Aiming at the defects existing in the currently sharing methods, a cross-platform data sharing method is proposed based on geospatial data model for sharing. Then taking ArcGIS and AutoCAD as example, the mapping relation of geospatial data sharing model and ArcGIS, AutoCAD geospatial data mode is put forward, and the two-way mapping between ArcGIS and AutoCAD is realized.(3) The unified expression and conversion of continuous geometry is carried out. Start from five types of continuous geometry in currently geospatial data model, the unified expression of continuous geometry in geospatial data are analyzed, so that to realize the unified expression of continuous geometry in geospatial data model, and simplify the GIS algorithm involved continuous geometry. The conversion of straight line segments, circle arcs, quadratic and cubic Bezier curve based on cubic NURBS curve are realized. The unified expression of five continuous geometric objects is resolved, in order to achieve the unity of expression and conversion of continuous geometric curve of geospatial data model. |
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