Study On Map Symbol Sharing Method Of GIS And CAD

Symbol is the carrier and the transmission tools of the geographic information. With the constantly plentiful of people understanding, recognization and classification spatial information, as the carrier of geographic information, symbol has changed correspondingly.However, the characteristic which symbol is a Graphic language of geographic information has not changed. With the constantly updating of the system which can collect,manage and edit geographic information,as the traditional research content of cartography field,symbol has been put forward the new requirements and challenges by all sorts of symbol data models. The difference among the different geographic information systems leads to the geographic information sharing is not synchronous with symbol sharing and the lose, deformation of symbol happens during the system interoperability.And the "homologous and heterogeneous" phenomenon had long existed in the GIS field, which is making a variety of formats of map symbol respectively based on the same kind of geography object to accommodate the corresponding platforms.Above these causes a large number of low-level repeat labor.At the same time, inside the geographic information system which is represented by GIS and CAD, the system interoperable framework itself is complex and diversiform and the specifications are not mature which also leads to the result that it is difficult to use the application framework to implement the interoperation between GIS and CAD platform.Therefore, guided by the constructing and sharing of the cross-platform symbol data model, based on the different process of abstracting spatial data model brings about the different spatial data model and symbol data model and further leads to the difference of the symbol data structure, the storage ways, the mapping strategy and the relating pattern of symbol and data in the spatial information system of GIS and CAD,the paper has analysised their substitutive characteristics respectively. Drawing lessons from the existing compositional imaging model,the composition rules of map symbol and the Method and technology of the unified expression of geometry, in order to change the current situation that it can not give consideration to symbol position, graphic and information simultaneously in the traditional symbol data sharing,a symbol data model which is oriented to the GIS and CAD cross-platform sharing has been put forward and the key questions of the nondestructive mapping between symbol data models and the output efficiency in the process of symbol cross-platform sharing has been brought through on emphases.The paper has provided the thought and method of solving to the above problems to realize the GIS and CAD symbols cross-platform sharing.The main research contents and the results are as follows:(1) The analysis of the difference between GIS and CAD symbol data models.From the different process of abstracting spatial data model between the two platforms, the paper has analysised the two different spatial data models of GIS and CAD and has mapped the difference of spatial data model to the symbol data model.And then the paper has analysised the characteristic of the two symbol data models from the four respects of the symbol data structure, the storage ways, the mapping strategy and the relating pattern of symbol and data, based on this, compared the difference of merits of symbol sharing methods at this stage and constructed the unified data model which is oriented to the GIS and CAD cross-platform sharing.(2) The construction of symbol data model which is oriented to the GIS and CAD cross-platform sharing.Based on the Postscript imaging model, the symbol data model which is centered in Path, Stroke and Fill has been proposed from map symbol composeition rules.Taking the point, line, polygon as the polymerization method, the paper has achieved the point, line and polygon symbol data model.And based on the cross-platform data model, the mapping relation between the AutoCAD, ArcGIS symbol model and the cross-platform symbol data model has been designed to achieve the unified description of the symbol data model between the two platforms.(3) The achievement of the unified expression of the geometry of the symbol data model and the adaptive interpolation method.A Path layered method in cross-platform symbol data model which includes the definition of Segment, Segment function conversion,and Segment output has been designed for the difference of the continuous and discrete geometry object in the symbol geometric graphics.The paper has elaborated the concepts, principles, procedures and implementation of each level,discussed the applicability of map symbol to improve the efficiency of the unified expression of the geometry and the adaptive interpolation calculation under the restriction output conditions inthe path hierarchical method.Through the ArcGIS and AutoCAD symbol sharing experiments.the feasibility of the cross-platform data model proposed in the paper and the methods designed in the paper can effectively solve the main problems existing in the process of the ArcGIS and AutoCAD symbol sharing.The paper has achieved the unified expression of the geometry and the adaptive interpolation calculation under the restriction output conditions.All these has provided the effective methods of the integrate of the geometric figure precision and the computational efficiency, eliminated the symbol isolated island between ArcGIS and AutoCAD, promoted the integration and sharing between GIS and CAD, provided new research methods and means for geographic information sharing and it is great important to improve the standardization of geographic information sharing.