Spatial indexing of global geographical data with HTM

Spatial indexing is one of the most important techniques in the field of spatial data management. Many kinds of techniques of spatial indexing have been successfully developed, and each of them has advantages towards special applications. As a type of spatial data structure, Hierarchical Triangular Mesh (HTM) has excellent features of global continuity, stability, hierarchy and uniformity, which has attracted much interest of researchers for many years. This paper investigates the method that using HTM as indexing for global geographical data (only point-like objects now). The HTM is defined by subdividing a unit sphere recursively and the basic elements in it are spherical triangles that are coded as integers called HTM codes in the computer system. At the global scale, all the regions on the sphere are spherical, which can be intersected with HTM elements obeying some equations. The spatial position of each input object can also be represented by a HTM code. HTM codes thus become the bridge between query regions and input objects. Our system is based on the combination of database management system (DBMS) and distributed file system. The major information of input files is extracted as metadata that are stored on tables of DBMS, while the original files are stored on the distributed file system (called HDFS) which has potential abilities to support parallel processing. Millions of point-like objects on the global were examined and the experiments indicated the system were acceptable.