grbindex

Introduction

The index file serves as a table of contents for the GRIB1 file, enabling quick access to the data.

For GRIB2 files, use grb2index.

There can be a gap before the first GRIB1 message of at most 32000 bytes and gaps between messages of at most 4000 bytes.

Usage

grbindex <GRIB1 file> <index filename>

The first argument is the name of the input GRIB1 file. The second argument is the name of the output index file.

Index File Format

Version 1 of the index file format is used with GRIB1 files, and has the following format:

• 81-byte "Steve Lord" header with 'GB1IX1' in columns 42-47
• 81-byte header with number of bytes to skip before index records, number of bytes in each index record, number of index records, and GRIB1 file basename written in format ('IX1FORM:',3i10,2x,a40).

Each following index record corresponds to a GRIB1 message and has the format. All integers are in big-endian format in the file.

• byte 001-004: bytes to skip in data file before GRIB1 message
• byte 005-008: bytes to skip in message before pds
• byte 009-012: bytes to skip in message before gds (0 if no gds)
• byte 013-016: bytes to skip in message before bms (0 if no bms)
• byte 017-020: bytes to skip in message before bds
• byte 021-024: bytes total in the message
• byte 025-025: GRIB version number
• byte 026-053: product definition section (pds)
• byte 054-095: grid definition section (gds) (or nulls)
• byte 096-101: first part of the bit map section (bms) (or nulls)
• byte 102-112: first part of the binary data section (bds)
• byte 113-172: (optional) bytes 41-100 of the pds
• byte 173-184: (optional) bytes 29-40 of the pds
• byte 185-320: (optional) bytes 43-178 of the gds