coord_vars.c File Reference

Demonstrates coordinate variables and CF convention metadata. More...

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

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

Functions
int	main ()

Detailed Description

Demonstrates coordinate variables and CF convention metadata.

This example introduces the concept of coordinate variables - special 1D variables that share the same name as their dimension and provide values along that axis. Coordinate variables are essential for geospatial data, defining latitude, longitude, time, or other dimensional coordinates.

The program creates a 2D temperature field (4x5 grid) with latitude and longitude coordinate variables following Climate and Forecast (CF) conventions. CF conventions are the standard metadata conventions for climate and forecast data.

Learning Objectives:

• Understand coordinate variables and their relationship to dimensions
• Learn CF convention metadata attributes (units, standard_name, long_name, axis)
• Master attribute definition and retrieval (nc_put_att, nc_get_att)
• Work with multi-dimensional geospatial data
• Implement proper metadata for scientific data interoperability

Key Concepts:

• Coordinate Variable: 1D variable with same name as its dimension (e.g., lat(lat))
• CF Conventions: Standardized metadata for climate/forecast data
• Attributes: Metadata attached to variables (units, standard_name, etc.)
• **_FillValue**: Special attribute indicating missing/undefined data values
• Geospatial Grid: Regular lat/lon grid for spatial data

CF Convention Attributes Used:

• units: Physical units (degrees_north, degrees_east, K)
• standard_name: CF standard name vocabulary (latitude, longitude, air_temperature)
• long_name: Human-readable descriptive name
• axis: Coordinate axis identifier (X, Y, Z, T)
• _FillValue: Value representing missing data

Prerequisites:

• simple_2D.c - Basic NetCDF file operations

Related Examples:

• f_coord_vars.f90 - Fortran equivalent
• unlimited_dim.c - Adds time dimension with unlimited size
• var4d.c - 4D data with time, level, lat, lon coordinates

Compilation:

gcc -o coord_vars coord_vars.c -lnetcdf

Usage:

./coord_vars
ncdump coord_vars.nc

Expected Output: Creates coord_vars.nc containing:

• 2 dimensions: lat(4), lon(5)
• 3 variables: lat(lat), lon(lon), temperature(lat,lon)
• CF-compliant metadata attributes
• Temperature data in Kelvin with lat/lon coordinates

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_vars.nc"

NLAT

#define NLAT   4

NLON

#define NLON   5

Function Documentation

main()

int main

(

)