Efficient encoding and decoding algorithm for triangular discrete global grid based on Hybrid Transformation Strategy

Abstract

Grid codes are an important part of a grid system and provide a unique identifier for the cells in the spherical triangular discrete global grid, where the transformation between geographic coordinates and grid codes is the basis of global spatial data integration and various analytical applications. Owing to the particularity of the topological properties, the spherical space cannot be continuously paved with the same grid cells as those in the plane space. Thus, the recursive approximation method is typically used to establish the transformation algorithm between the geographic coordinates and the grid codes. The efficiency of those algorithms that were based on recursive approximation obviously decreased with the increased grid subdivision level; thus, it is not conducive to the integration of massive high-resolution spatial data. Whereas the geometric properties of the grid cells in the spherical triangular discrete global grid differ during the initial subdivision levels, as the level increases, these geometric properties tend to be the same, along with the properties of the local regions similar to the plane. Considering this characteristic, this paper proposes a hybrid bidirectional transformation algorithm. In the proposed algorithm, the recursive approximation method is used at the lower level where there is a large difference in the geometrical properties of the grid cells, and the direct mapping method using a similar plane grid is used at the higher level where the geometrical properties of the grid cells are virtually the same. In experiments conducted using the proposed algorithm with geographic coordinates at different scales and grid codes at different levels, the running time remained stable with no significant change throughout increases in the hierarchical level. Further, it was proven to satisfy the requirements of the absolute accuracy evaluation method. Compared with the traditional recursive approximation algorithm, the proposed algorithm has obvious advantages in the transformation between grid codes and geographic coordinates, as it can better support spatial data integration and various analytical applications in the spherical triangular discrete global grid system.