摘要:
三维电子地图表达客观世界具有形象直观的优势，对三维地理环境的表达与认知具有重要意义。传统三维电子地图数据量大，数据格式多样，使用时依赖专业软件工具，具有一定的用图难度。信息化时代，普通用户对便携式文档格式（portable document format，PDF）比较熟悉，PDF格式具有更好的通用性和普适性。为适应地图大众化应用趋势，降低普通用户用图难度，探索设计了一种新型三维PDF地图数据组织模型，基于PDF便携式文档格式形式化表达三维地图。首先，归纳了三维PDF地图的概念，设计了数据组织结构与数据存储结构。其次，基于该组织模型分别利用地形数据、倾斜摄影数据、城市三维数据开展了三维PDF地图制作试验。最后，讨论分析了三维PDF地图数据组织模型所具备的典型特征。试验表明，三维PDF地图图面清晰美观，具备地图基本特征与PDF轻量化特征。该研究为地图用户提供了一种基于PDF便携式文档格式的三维地图解决方案，有助于拓展三维电子地图的用户群体和应用场景。
Abstract:
Objectives: The three-dimensional (3D) electronic map has the advantage of representing the objective world in a vivid and intuitive way, which is of great significance for the abstract simulation and cognition of the three-dimensional geographical environment. Traditional 3D electronic maps have a large amount of data, diverse data formats, and rely on professional software tools, which increases the difficulty of using maps. In the era of informatization, ordinary users are familiar with the portable document format (PDF), and the PDF format has better universality. In order to adapt to the trend of popular map application and reduce the difficulty of ordinary users to use maps, this paper explores the design of a new type of 3D map data organization model -- 3D Geospatial PDF Map Data Organization Model, which formally expresses 3D maps based on PDF format. Methods: Firstly, we elaborate the concept of 3D geospatial PDF map, designed the data organization structure and propose the organizational structure of 3D geospatial PDF map. We also designed the data storage structure based on the PDF format and the Universal 3D (U3D) model. Secondly, based on our 3D geospatial PDF map data organization model, experiments were conducted on the production of 3D geospatial PDF maps using terrain data, oblique photography 3D data, and urban 3D data. Finally, we discuss and analyze the typical features of 3D geospatial PDF map data organization model. Results: (1) Three 3D geospatial PDF map were produced based on our 3D geospatial PDF map data organization model, with clear and beautiful visual effects; (2) 3D geospatial PDF map has both basic map features and PDF lightweight features, namely, map scene element visualization, geospatial reference, three-dimensional geographic entity structure, storage lightweight, form lightweight and application lightweight. Conclusions： This research provides map users with a 3D map solution based on the PDF format, which is helpful to expand the user group and application scenarios of 3D electronic map.
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