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sfc_pres_temp_wr.c
/* Copyright 2019 University Corporation for Atmospheric
Research/Unidata. See COPYRIGHT file for conditions of use. */
#include <stdio.h>
#include <string.h>
#include <netcdf.h>
/* This is the name of the data file we will create. */
#define FILE_NAME "sfc_pres_temp.nc"
/* We are writing 2D data, a 6 x 12 lat-lon grid. We will need two
* netCDF dimensions. */
#define NDIMS 2
#define NLAT 6
#define NLON 12
#define LAT_NAME "latitude"
#define LON_NAME "longitude"
/* Names of things. */
#define PRES_NAME "pressure"
#define TEMP_NAME "temperature"
#define UNITS "units"
#define DEGREES_EAST "degrees_east"
#define DEGREES_NORTH "degrees_north"
/* These are used to construct some example data. */
#define SAMPLE_PRESSURE 900.0f
#define SAMPLE_TEMP 9.0f
#define START_LAT 25.0f
#define START_LON -125.0f
/* Handle errors by printing an error message and exiting with a
* non-zero status. */
#define ERR(e) {printf("Error: %s\n", nc_strerror(e)); return 2;}
int
main()
{
int ncid, lon_dimid, lat_dimid, pres_varid, temp_varid;
/* In addition to the latitude and longitude dimensions, we will also
create latitude and longitude netCDF variables which will hold the
actual latitudes and longitudes. Since they hold data about the
coordinate system, the netCDF term for these is: "coordinate
variables." */
int lat_varid, lon_varid;
int dimids[NDIMS];
/* We will write surface temperature and pressure fields. */
float pres_out[NLAT][NLON];
float temp_out[NLAT][NLON];
float lats[NLAT], lons[NLON];
/* It's good practice for each netCDF variable to carry a "units"
* attribute. */
char pres_units[] = "hPa";
char temp_units[] = "celsius";
/* Loop indexes. */
int lat, lon;
/* Error handling. */
int retval;
/* Create some pretend data. If this wasn't an example program, we
* would have some real data to write, for example, model
* output. */
for (lat = 0; lat < NLAT; lat++)
lats[lat] = START_LAT + 5.F*(float)lat;
for (lon = 0; lon < NLON; lon++)
lons[lon] = START_LON + 5.F*(float)lon;
for (lat = 0; lat < NLAT; lat++)
for (lon = 0; lon < NLON; lon++)
{
pres_out[lat][lon] = SAMPLE_PRESSURE + (float)(lon * NLAT + lat);
temp_out[lat][lon] = SAMPLE_TEMP + .25f * (float)(lon * NLAT + lat);
}
/* Create the file. */
if ((retval = nc_create(FILE_NAME, NC_CLOBBER, &ncid)))
ERR(retval);
/* Define the dimensions. */
if ((retval = nc_def_dim(ncid, LAT_NAME, NLAT, &lat_dimid)))
ERR(retval);
if ((retval = nc_def_dim(ncid, LON_NAME, NLON, &lon_dimid)))
ERR(retval);
/* Define coordinate netCDF variables. They will hold the
coordinate information, that is, the latitudes and longitudes. A
varid is returned for each.*/
if ((retval = nc_def_var(ncid, LAT_NAME, NC_FLOAT, 1, &lat_dimid,
&lat_varid)))
ERR(retval);
if ((retval = nc_def_var(ncid, LON_NAME, NC_FLOAT, 1, &lon_dimid,
&lon_varid)))
ERR(retval);
/* Define units attributes for coordinate vars. This attaches a
text attribute to each of the coordinate variables, containing
the units. Note that we are not writing a trailing NULL, just
"units", because the reading program may be fortran which does
not use null-terminated strings. In general it is up to the
reading C program to ensure that it puts null-terminators on
strings where necessary.*/
if ((retval = nc_put_att_text(ncid, lat_varid, UNITS,
strlen(DEGREES_NORTH), DEGREES_NORTH)))
ERR(retval);
if ((retval = nc_put_att_text(ncid, lon_varid, UNITS,
strlen(DEGREES_EAST), DEGREES_EAST)))
ERR(retval);
/* Define the netCDF variables. The dimids array is used to pass
the dimids of the dimensions of the variables.*/
dimids[0] = lat_dimid;
dimids[1] = lon_dimid;
if ((retval = nc_def_var(ncid, PRES_NAME, NC_FLOAT, NDIMS,
dimids, &pres_varid)))
ERR(retval);
if ((retval = nc_def_var(ncid, TEMP_NAME, NC_FLOAT, NDIMS,
dimids, &temp_varid)))
ERR(retval);
/* Define units attributes for vars. */
if ((retval = nc_put_att_text(ncid, pres_varid, UNITS,
strlen(pres_units), pres_units)))
ERR(retval);
if ((retval = nc_put_att_text(ncid, temp_varid, UNITS,
strlen(temp_units), temp_units)))
ERR(retval);
/* End define mode. */
if ((retval = nc_enddef(ncid)))
ERR(retval);
/* Write the coordinate variable data. This will put the latitudes
and longitudes of our data grid into the netCDF file. */
if ((retval = nc_put_var_float(ncid, lat_varid, &lats[0])))
ERR(retval);
if ((retval = nc_put_var_float(ncid, lon_varid, &lons[0])))
ERR(retval);
/* Write the pretend data. This will write our surface pressure and
surface temperature data. The arrays of data are the same size
as the netCDF variables we have defined. */
if ((retval = nc_put_var_float(ncid, pres_varid, &pres_out[0][0])))
ERR(retval);
if ((retval = nc_put_var_float(ncid, temp_varid, &temp_out[0][0])))
ERR(retval);
/* Close the file. */
if ((retval = nc_close(ncid)))
ERR(retval);
printf("*** SUCCESS writing example file sfc_pres_temp.nc!\n");
return 0;
}
nc_put_att_text
EXTERNL int nc_put_att_text(int ncid, int varid, const char *name, size_t len, const char *op)
Write a text attribute.
Definition dattput.c:153
nc_close
EXTERNL int nc_close(int ncid)
Close an open netCDF dataset.
Definition dfile.c:1300
nc_create
EXTERNL int nc_create(const char *path, int cmode, int *ncidp)
Create a new netCDF file.
Definition dfile.c:398
nc_enddef
EXTERNL int nc_enddef(int ncid)
Leave define mode.
Definition dfile.c:1027
nc_def_dim
EXTERNL int nc_def_dim(int ncid, const char *name, size_t len, int *idp)
Define a new dimension.
Definition ddim.c:121
nc_def_var
EXTERNL int nc_def_var(int ncid, const char *name, nc_type xtype, int ndims, const int *dimidsp, int *varidp)
Define a new variable.
Definition dvar.c:214
netcdf.h
Main header file for the C API.
NC_CLOBBER
#define NC_CLOBBER
Destroy existing file.
Definition netcdf.h:138
NC_FLOAT
#define NC_FLOAT
single precision floating point number
Definition netcdf.h:40