JIA-2018-09

1921 Yanbo Huang et al. Journal of Integrative Agriculture 2018, 17(9): 1915–1931 –90°(South Pole) to +90° (North Pole). If the left lower corner is used as the origin, the ranges of horizontal and vertical axis become [0°, 360°] and [0°, 180°], respectively. With the interval of 36°, the first level can be cut into 10 slices horizontally and 5 slices vertically. Therefore, the global map can be divided into 50 blocks at the level. Similarly, with the interval of 18°, the global map can be divided into 200 blocks with 20 horizontal slices and 10 vertical slices at the second level. And so on, the numbers of blocks in the global map at all other follow-up levels can be calculated out. In data storage, regardless of levels, each block corresponds a 512×512 image and the block can be recognized with the block number on the coordinate system with the latitude and longitude. The method for World Wind to divide the global map at different levels is often used to visualize images at different resolutions on the 3D sphere. However, the method with such intervals leads to the problem of floating numbers. For example, at the eighth level, the size of the block is 0.28125°×0.28125°. Manipulation of floating numbers may cause problems in computer processing of remote sensing data. It may lose computing precision significantly, and at the same time, it may cause inaccurate mapping of sphere texture (Clasen and Hege 2006). In addition World Wind’s 512×512 image size with different block sizes at different resolutions cannot compute with commonly usedmap scales. 3.5. Five-layer-fifteen-level remote sensing data management Scientists in the Institute of Remote Sensing and Digital Earth (former Institute of Remote Sensing Applications), Chinese Academy of Science (CAS) developed an innovative five- layer-fifteen-level (FLFL) remote sensing data management structure (Wang et al. 2012; Yu et al. 2012; Gu et al. 2013). The FLFL structure is used to block the sphere surface of the earth with each block filled with a 1000×1000 image. Each of the five layers has three levels with a size proportion of 5:2.5:1. The size difference between layers is 10. Therefore, the sizes of the three blocks in the first layer are 50°×50°, 25°×25° and 10°×10° in sequence. The block sizes in the second layer are 5°×5°, 2.5°×2.5° and 1°×1°. And so on for the layers of 3, 4 and 5. This data management structure is well fitted for remote sensing data organization with the grid of latitude and longitude to match up with the commonly used map scales. Table 3 illustrates the scheme for remote sensing data blocking with the FLFL structure. Fig. 1 shows the image blocks of a MODIS image covering the area of longitude in [270°, 320°] and latitude in [130°, 160°] with the FLFL scheme (the origins of the latitude and longitude were redefined to avoid negative values for the blocking algorithm). With 1 km image resolution, the corresponding block size is 10° and the Original image Blocked image Naming convention: Where, P, product; M, MODIS; T, Sensor (Terra); 1KM, resolution; yyyy, year; mm, month; dd, day; level, data level; LAT, latitude; LON, longitude. P()M(T)1KMyyyymmdd_Level_LAT_LON.suffix 160° 150° 140° 130° 270° 280° 290° 300° 310° 320° Fig. 1 MODIS image FLFL (five-layer-fifteen-level) blocking and naming convention.