| Geo PDF is an emerging file format for map storage. Except for storing texts and images,Geo PDF additionly stores some geographic system information related to map content.Compared to the traditional format, Geo PDF is a better one which is more convenient and has attracted great attention in society. For ordinary Geo PDF browser on the market, there is a common drawback that they do not support multi-document in single view. So for users who want to conveniently browse several documents in one view, the current Geopdf readers will not satisfy. To solve the above problem, this paper designs and realizes a system supports browsing multi-Geo PDF map files.Geo PDF browsing system separates the map display, the map operation and the map data management into three independent models: view module, interface module and data management module,referring to the MVC architecture. In the realization of the whole system, the main research contents and achievements of this paper are as follows:1. Deeply study the standard of PDF file and Geo PDF file, understand the way PDF and Geo PDF stores map information. And then successfully get map information from Geo PDF by using a third part library.2. Study and analyze the mechanism of drawing map, design and realize a efficient drawing Geo PDF map scheme. The basic idea of the scheme is merging several drawing requests into one quest and response to drawing quest as much as possible in each drawing process,which improve the drawing efficiency.3. Study the characteristics of GeoPDF map, put forward a GeoPDF map cache system which is different from traditional map cache systems. The cache system adopts a special grid cache structure which has the characteristics of unchanged memory size and ability of splicing several Geo PDF into one cache grid unit. In this way, the problems in file splicing and the recovery of memory encountered in browsing Geo PDF map can be resolved effectively.4. Deeply study the mechanism of rendering a Geo PDF map, design and realize a scheme rendering Geo PDF map parallelly and efficiently. This scheme design a efficient rendering task queue at first, then design a Geo PDF object management module which can distinguish Geo PDF status and an efficient cache replacement algorithm. At last, design a complex concurrent multi task system, realize efficiency map rendering.5. Study the problem of data mismatch between Geo PDF and framework.Design an abstract Geo PDF geographical model and a method converting geographical elements into the abstract data model. After that, the mismatch problem between framework and Geo PDF data was solved... |
