Objectives Vector geospatial PDF (portable document format) map is a new type of electronic map, which has the characteristics of small data size, strong generality, etc., and has the function of geospatial query and calculation. Its applying needs and prospects are broad. As the method by using digital line graphic (DLG) data only, to make vector geospatial PDF map through symbolization and cartographic editing has a long process and heavy workload, it is of great significance to make full use of the existing map data to quickly produce vector geospatial PDF map. As result, it avoid affecting the existing map production process, and improve the vector geospatial PDF map making more efficient.
Methods This paper presents a quick method of making vector geospatial PDF map, which uses publication origins of map (POM) and DLG data by data preprocessing, map coordinate system construction, data aggregation and compression. (1) Data preprocessing. Based on multi-source spatial data engine, POM and DLG data sources are loaded, integrated and utilized. Through the process of feature layer extraction, entity type extraction, coordinate extraction and attribute extraction, the useful and important objects in DLG are extracted. The POM data is processed by combining different color pages, replacing and overprinting layers, and setting the minimum page range. Select control points with known coordinates in POM page. We have completed the data preparation of vector geographic PDF map making. (2) Construction of map coordinate system. The map coordinate system model is designed and defined as a composite of six coordinate systems including DCS (data source coordinate system), GCS (geometric coordinate system), PCS (projection coordinate system), ECS (equal scale map coordinate system), FCS (file coordinate system) and OCS (output coordinate system). It also defined a series of mutual transformation parameters and functions. The coordinate system of the map is solved by knowing the coordinates of the control points and the rotation angle of the map. The coordinate registration of POM and DLG data is completed by using six coordinate system transformation parameters. (3) Data aggregation and compression. The POM with map graphical information and DLG with geographic information extracted are aggregated in the coordinate system after registration to generate a new PDF file. Using a variety of methods, the redundant data of PDF file is compressed without reducing the data accuracy. And a new vector geographic PDF map is generated.
Results This method omits the process of symbolization and cartographic editing. The experimental results show that the efficiency of making vector geospatial PDF map is high, and the map results data size is significantly compressed compared with the total amount of POM and DLG Data.
Conclusions It is suitable for large-scale rapid production of vector geospatial PDF map with DLG and POM data source conditions.
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