coord.c File Reference

Demonstrates 3D surface temperature with time, lat, lon coordinate variables. More...

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netcdf.h>

Macros
#define	FILE_NAME   "coord.nc"
#define	NTIME   3
#define	NLAT   4
#define	NLON   5
#define	NDIMS   3
#define	ERRCODE   2
#define	ERR(e)   {printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}

Functions
int	main ()

Detailed Description

Demonstrates 3D surface temperature with time, lat, lon coordinate variables.

This example builds on coord_vars.c by adding a time dimension, creating a 3D surface temperature field with latitude, longitude, and time coordinate variables. It demonstrates how to work with three-dimensional data and follows Climate and Forecast (CF) conventions for all coordinate metadata, including the time axis.

The program creates a surface temperature dataset on a 4x5 lat/lon grid with 3 time steps, writes it to a classic NetCDF file, then reopens and validates all contents.

Learning Objectives:

• Work with 3D data (time, lat, lon)
• Define time coordinate variables with CF conventions
• Use the CF calendar attribute for time coordinates
• Add the coordinates attribute to data variables (CF best practice)
• Create classic-format NetCDF files (no HDF5 dependency)
• Validate multi-dimensional data after writing

Key Concepts:

• 3D Data: Surface temperature varying over space and time
• Time Coordinate: 1D variable with CF time attributes (units, calendar, axis)
• **coordinates Attribute**: Explicitly links data variables to their coordinate variables, a CF convention best practice
• Classic Format: Uses NC_CLOBBER (classic NetCDF) rather than NC_NETCDF4

CF Convention Attributes Used:

• units: Physical units (degrees_north, degrees_east, hours since ..., K)
• standard_name: CF standard name vocabulary
• long_name: Human-readable descriptive name
• axis: Coordinate axis identifier (X, Y, T)
• calendar: Calendar type for time coordinates (standard)
• _FillValue: Value representing missing data
• coordinates: Lists coordinate variables for a data variable

Prerequisites:

• coord_vars.c - 2D coordinate variables and CF metadata

Related Examples:

• f_coord.f90 - Fortran equivalent
• coord_vars.c - 2D version without time dimension
• unlimited_dim.c - Using unlimited dimensions for time series
• var4d.c - 4D data with time, level, lat, lon

Compilation:

gcc -o coord coord.c -lnetcdf

Usage:

./coord
ncdump coord.nc

Expected Output: Creates coord.nc containing:

• 3 dimensions: time(3), lat(4), lon(5)
• 4 variables: time(time), lat(lat), lon(lon), sfc_temp(time,lat,lon)
• CF-compliant metadata attributes on all variables
• Surface temperature data in Kelvin

Author

Edward Hartnett, Intelligent Data Design, Inc.

Date

2026

Macro Definition Documentation

ERR

#define ERR

(

e

)

{printf("Error: %s\n", nc_strerror(e)); exit(ERRCODE);}

ERRCODE

#define ERRCODE   2

FILE_NAME

#define FILE_NAME   "coord.nc"

NDIMS

#define NDIMS   3

NLAT

#define NLAT   4

NLON

#define NLON   5

NTIME

#define NTIME   3

Function Documentation

main()

int main

(

)