Introduction

The NetCDF User’s Guide (NUG) describes various netCDF concepts and details that may be of interest to all netCDF users, independent of what library/tool they use. The NUG provides high-level descriptions of netCDF concepts useful to users and creators of netCDF data (e.g., data users, data producers, data managers, and tool developers). It also provides the details and specifications needed by developers and maintainers of any netCDF implementations (e.g. netCDF-4 based on HDF5 for h5netcdf, ncZarr based on Zarr for netCDF-java).

The NUG describes and specifies the details of

• the netCDF data models
• the netCDF file formats and encodings
• the netCDF CDL (Common Data form Language), a text notation for representing the structure and data of a binary netCDF dataset

The NUG also:

• provides a list of known implementations, libraries, APIs
• provides a set of Best Practices
• defines a basic set of attribute conventions (e.g., units, valid_min, and scale_factor/add_offset)
• provides references to other community conventions (e.g., CF, UGRID) - see current list/page
• How to use netCDF (gallery of tools)

Use of CDL in this Document

Throughout the NUG, we will use the CDL (netCDF Comman Data Language) text notation to present the content and structure of netCDF datasets for all examples.

A simple CDL example is shown here

netcdf minimal_example {   // very simple example of CDL notation
    dimensions:
        lon = 3 ;
        lat = 8 ;
    variables:
        float rh(lon, lat) ;
            rh:units = "percent" ;
            rh:long_name = "Relative humidity" ;
    // global attributes
    :title = "Simple example" ;

    data:
        rh =
            2, 3, 5, 7, 11, 13, 17, 19,
            23, 29, 31, 37, 41, 43, 47, 53,
            59, 61, 67, 71, 73, 79, 83, 89 ;
}

A full description of CDL, along with discussion and more detailed examples, can be found on the “Common Data Language” page.