Research On Technologies For Fast Seamless Roaming Around Multiple Large-size PDF Maps

PDF is a simple,portable,cross-platform and publication-level electronic file format,and is widely used in various fields.GeoPDF based on the PDF standard,which incorporates spatial reference information and geographic data information,has become a new map file format.It not only has the advantages of traditional PDF,but also can do some related operations on geographic information by using special tools,which can be completed by using professional GIS products,such as map plot,distance measurement,location query,etc.At present,GeoPDF browsers in market are generally implemented by adding map plugins to conventional PDF browsers.However,the biggest problem in these GeoPDF browsers is that only one map file can be opened at a time,which is inconvenient for some map applications that span multiple maps,and it also greatly restricts the application of GeoPDF maps.In order to implement the seamless roaming operation of GeoPDF maps,it is necessary to design a GeoPDF browser to solve this problem.Based on this,this thesis first designs a multi-functional map browser,which adopts the object-oriented design concept and implements such functional modules as layer management,data management,coordinate conversion,and auxiliary tools,which not only support the basic scaling,roaming,distance measurement,but also support transparent overlay between multiple layers.Then,based on this,this thesis designs a nine-grid model to solve the problem of seamless roaming of large-size GeoPDF.The concrete implementation of this model is mainly divided into the following three parts:(1).GeoPDF parallel rendering: This procedure uses multi-task technology,encapsulates and distributes rendering subtasks by the main process,the subprocess receives the task,performs the rendering task,and returns the rendering results by asynchronous way,to complete parallel rendering task of GeoPDF maps.(2).GeoPDF real-time display: This procedure uses technology of multithreading and drawing queue,and puts the rendering results into the drawing queue by using asynchronous multi-thread way.And then,main process completes the real-time display of GeoPDF maps by executing drawing operations.(3).GeoPDF full-range roaming: This procedure uses process-reuse and dynamical map replacement technology to complete the full-range roaming operations of GeoPDF maps.Based on the above content,this thesis finally implements a map browser with full function,high performance,convenient operation,which supports seamless roaming operations of GeoPDF maps.Besides,this thesis adopts many optimization methods to improve the rendering speed of GeoPDF,such as partial rendering,thumbnails and subprocess cache replacement.It is a complete solution of GeoPDF with the features of cross document and fast roaming.