Index Files

The data location files are called index files, and one is created for each image type detected in the SDFs. An index file consists of a series of text lines, one for each data block or frame in the image. If the image consists of 1800 blocks, its index file contains 1800 text lines. Each text line describes the location of a data block in an SDF that is required to create the complete image. For example, if a certain image consists of 1,000 blocks distributed in 400 SDFs, its index file has 1,000 ASCII text lines. Since the index files are in ASCII format, they can be viewed using most Unix file viewing commands.

Index file text entries are generated by an SDF scanning process that looks for the beginnings of blocks. When a block's beginning is located, its length, type and location information, including the SDF file name, are formed into a text line and stored in the appropriate index file.

For some satellites, multiple index files are created simultaneously. For example, GVAR imager data block descriptions are stored in one index file (Blocks 0 through 10), while all Block 11 descriptions are stored in another index file.

Index File Format

The index file format is different for different satellites types. Refer to the index file Format description in the satellite-specific chapter for a complete description of the index file format for your ingestor.

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