After generating image pyramids from image data, different resolution layers are obtained. The system determines the start and end levels, and assigns level numbers to each layer based on resolution. Level 1 corresponds to the lowest resolution image layer, Level 2 to higher resolution than Level 1, and Level 3 to the highest resolution.

The generated tile results vary depending on storage types.

1. When using "Original" storage type:
   • Following global geographic coordinate system rules, each level's image data is divided into blocks. Each block's data is saved as a tile file named: nRow_nCol_nVersion.postfix

     Where:
     nRow: Row number in global grid (minimum 4 characters, zero-padded)
     nCol: Column number in global grid (minimum 4 characters, zero-padded)
     nVersion: Tile version number (default: 0000)
     Postfix: File extension (default: *.png)

   • Group tile files using "Grouping Grid" rules for storage organization.
2. When using "Compact" storage type:
   • Compress and encrypt all tile files within a group into three files: Name.~, Name.sc, Name.sc00

     Where Name represents the tile root directory name (e.g., day)

SuperMap employs a global geographic coordinate system-based quad-tree tiling mode for terrain/image data division. This establishes a unified global grid subdivision model applicable to both global-scale and regional-scale data. The system supports maximum 21 levels, with Level 0 corresponding to the coarsest resolution layer in image pyramids.

Block Division

The global geographic coordinate system uses square grids for data partitioning. Level 0 divides the globe into 2 blocks (180°×180° each), Level 1 into 8 blocks (90°×90° each), and subsequent levels follow binary subdivision (quad-tree partitioning).

Figure: Global Rule of Geographic Coordinate System

Each block's geographic extent is determined by its level. Block positions are identified by row/column numbers starting from (0,0) at (-180°,90°). Higher levels produce smaller blocks with finer resolutions.

Illustrations below show Level 1-3 block division results with corresponding tile filenames:

Figure: Level 1 Block Division of Day Image Data

Figure: Level 2 Block Division of Day Image Data

Figure: Level 3 Block Division of Day Image Data

• Level 1 division result of day image data
• Level 2 division result of day image data
• Level 3 division result of day image data

Grouping Grid

Grouping grids organize tile files by defining row and column grouping spans (row_step and col_step). Each group contains row_step rows and col_step columns of blocks.

Calculation formulas:

Determining Row Folders per Level Row folder count calculation: Where: x = intermediate variable n = current level number floor() = floor function pow() = exponential function row = number of row folders (0000-indexed) row_image = total rows in current level row_step = row grouping span Determining Column Folders per Row Folder Column folder count calculation: Where: col_setp = 2 × row_step col = number of column folders (0000-indexed) col_image = total columns in current level

Figure: Level 1 Grouping Grid of Day Image Data

Figure: Level 2 Grouping Grid of Day Image Data

Figure: Level 3 Grouping Grid of Day Image Data

• Level 1: row_step=1, col_step=2
• Level 2: row_step=2, col_step=4
• Level 3: row_step=2, col_step=4