GRIB1 Decoder in C++

A C++ decoder for GRIB Edition 1 messages based on the WMO FM 92 GRIB specification, using template 388. This decoder parses and extracts meteorological and oceanographic data from GRIB1 binary files, which are widely used in numerical weather prediction and climate modeling.

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Features

• Parses all relevant sections of a GRIB1 message (0, 1, 2, 4, 5)
• Supports verification of message length integrity
• Extracts and decodes meteorological parameters such as temperature
• Handles GDS and BMS presence flags, decimal and binary scaling
• Outputs detailed, human-readable data reports per message
• Designed for educational and research purposes

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Output Description

The decoder generates a detailed, structured textual report for each processed GRIB message. The output is divided into sections corresponding to the GRIB1 message structure:

• SECTION 0
  Displays the total length of the message and the length of section 0.

• SECTION 1 (Product Definition Section - PDS)
  Provides metadata including:

  • Length of the PDS section
  • Presence flags indicating if the Grid Description Section (GDS) and Bit-map Section (BMS) are included
  • Message timestamp (date and time)
  • Decimal scale factor used in data decoding
  • Type indicator of the vertical level or layer
  • Pressure level in hectopascals (hPa), if applicable

• SECTION 2 (Grid Description Section - GDS)
  Details about the spatial grid, including:

  • Length of the GDS section
  • Geographic coordinates marking the start and end points of the data octant (latitude and longitude)
  • Number of rows in the data grid
  • Increment step in the North-South direction
  • Reserved fields
  • Number of data points per grid row

• SECTION 4 (Binary Data Section - BDS)
  Contains parameters for binary data decoding:

  • Length of the BDS section
  • Binary scale factor
  • Reference (minimum) data value
  • Number of bits used per encoded data value
  • Sample decoded raw values from the data stream

• SECTION 5
  Usually a short section indicating length (commonly 4 bytes).

• Decoded Meteorological Data
  Provides human-readable physical values extracted from the binary data, for example temperature values in degrees Celsius.

Each message is saved as a separate text file (e.g., Data_1.txt), facilitating further analysis and verification.

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Prerequisites

• A C++17 (or later) compatible compiler
• Standard C++ libraries

Building

Compile the decoder using your preferred compiler. For example, using g++:

Author

Created for educational purposes by Avui.