菱形三十面体格网系统构建的等积投影方法研究

Research on the Equal-Area Projection for the Construction of the Rhombic Triacontahedron Grid Systems

  • 摘要: 全球离散格网系统(discrete global grid systems,DGGS)是一类新兴的数字地球参考框架,在大尺度多源地理空间数据集的组织、集成与分析方面具有天然优势。现有全球离散格网系统构建方法中,基于多面体投影方法生成的格网系统具有更加优异的几何性质,因而被广泛研究。基础多面体及投影方法是格网系统设计选项中影响格网单元几何性质的主要因素。为构建更加均匀、高效的格网系统,本文选择菱形三十面体作为基础多面体,推导菱形三十面体与地球球体等积投影的正反算解析公式,并将其应用于三种不同单元形状等积全球离散格网的生成。对比实验结果表明,与二十面体 Snyder 等积投影相比,本文提出方法的角度变形减小约 51%,且克服了 Snyder 逆投影迭代求解导致格网生成效率较低的不足,为全球离散格网系统的相关应用提供了优选解决方案。

     

    Abstract: Objectives: Discrete global grid systems (DGGS) are new reference frameworks for the Digital Earth, and are suitable for organization, integration and analysis of multi-source big geospatial datasets. Among the existing construction methods of DGGS, using polyhedron projection to the sphere can generate DGGS with superior geometric properties and has been widely used at present. Basic polyhedrons and projection methods are main factors of DGGS design choices with respect to grid cell geometrics. Most existing DGGS schemes choose the platonic solids to approximate the Earth, where the icosahedron achieves the smallest distortion due to the most faces but still has difference with spherical surface. To break through the thinking of platonic solids and constructs more uniform and efficient grid systems, this paper chooses a new basic polyhedron, the rhombic triacontahedron, and researches its equal-area projection methods. Methods: The "Slice-and-Dice" approach provides the equal-area mapping between the spherical triangles and the planar triangles for the polyhedral projections, which has different implementations according to the partitioning strategies, and in this paper the vertex-oriented great circle projection is chosen to realize the equal-area mapping between the surface of the rhombic triacontahedron and the sphere because of more uniform angular distortion compared with the Snyder equal-area polyhedral projection. Each diamond face of the rhombic triacontahedron is divided into two triangles along the short diagonal as the basic planar triangles for projection. First, according to the equal surface area of the rhombic triacontahedron and the sphere, we calculate the edge and angle parameters of the rhombic triacontahedron and its corresponding spherical polyhedron. Then, the forward and inverse projection formulas are derived based on the equal-area conditions of the vertex-oriented great circle projection. All procedures are closed form without iterations like the inverse Snyder equal-area polyhedral projection. Results: Three experiments are realized and the results show that: (1) compared with the icosahedron using Snyder equal-area polyhedral projection, the angular distortion caused by the proposed method is reduced by 51%. The mean of angular distortion declines from 0.166 radians to 0.082 radians, and the standard deviation declines from 0.055 to 0.023; (2) the proposed scheme is used to generate three types of global grids with different cell shapes—triangles, quadrilaterals and the hexagons, which verifies the validity of the proposed scheme; (3) the efficiency of grid generation using the proposed inverse projection of the rhombic triacontahedron is about four times that of the icosahedron grids based on the inverse Snyder equal-area projection, which needs iterations. Conclusions: A new DGGS scheme is proposed by introducing the rhombic triacontahedron, which provides a new idea for the development and application of DGGS. The new scheme has more angular distortion, which helps generate more uniform grids and improve the accuracy of subsequent data processing and representation, and can be applied to different cell shapes. The next step is to research data modeling, spatial analysis algorithms and the combination of DGS and high-performance computing based on this scheme, so as to provide better solutions for the organization, processing and analysis of big data on the Earth.

     

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