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pres_temp_4D_wr.c
Go to the documentation of this file.
/* 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 "pres_temp_4D.nc"
/* We are writing 4D data, a 2 x 6 x 12 lvl-lat-lon grid, with 2
timesteps of data. */
#define NDIMS 4
#define NLAT 6
#define NLON 12
#define LAT_NAME "latitude"
#define LON_NAME "longitude"
#define NREC 2
#define REC_NAME "time"
#define LVL_NAME "level"
#define NLVL 2
/* 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
/* For the units attributes. */
#define UNITS "units"
#define PRES_UNITS "hPa"
#define TEMP_UNITS "celsius"
#define LAT_UNITS "degrees_north"
#define LON_UNITS "degrees_east"
#define MAX_ATT_LEN 80
/* 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()
{
/* IDs for the netCDF file, dimensions, and variables. */
int ncid, lon_dimid, lat_dimid, lvl_dimid, rec_dimid;
int lat_varid, lon_varid, pres_varid, temp_varid;
int dimids[NDIMS];
/* The start and count arrays will tell the netCDF library where to
write our data. */
size_t start[NDIMS], count[NDIMS];
/* Program variables to hold the data we will write out. We will only
need enough space to hold one timestep of data; one record. */
float pres_out[NLVL][NLAT][NLON];
float temp_out[NLVL][NLAT][NLON];
/* These program variables hold the latitudes and longitudes. */
float lats[NLAT], lons[NLON];
/* Loop indexes. */
int lvl, lat, lon, i = 0;
/* 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 (lvl = 0; lvl < NLVL; lvl++)
for (lat = 0; lat < NLAT; lat++)
for (lon = 0; lon < NLON; lon++)
{
pres_out[lvl][lat][lon] = SAMPLE_PRESSURE + (float)i;
temp_out[lvl][lat][lon] = SAMPLE_TEMP + (float)i++;
}
/* Create the file. */
if ((retval = nc_create(FILE_NAME, NC_CLOBBER, &ncid)))
ERR(retval);
/* Define the dimensions. The record dimension is defined to have
* unlimited length - it can grow as needed. In this example it is
* the time dimension.*/
if ((retval = nc_def_dim(ncid, LVL_NAME, NLVL, &lvl_dimid)))
ERR(retval);
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);
if ((retval = nc_def_dim(ncid, REC_NAME, NC_UNLIMITED, &rec_dimid)))
ERR(retval);
/* Define the coordinate variables. We will only define coordinate
variables for lat and lon. Ordinarily we would need to provide
an array of dimension IDs for each variable's dimensions, but
since coordinate variables only have one dimension, we can
simply provide the address of that dimension ID (&lat_dimid) and
similarly for (&lon_dimid). */
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);
/* Assign units attributes to coordinate variables. */
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);
/* The dimids array is used to pass the dimids of the dimensions of
the netCDF variables. Both of the netCDF variables we are
creating share the same four dimensions. In C, the
unlimited dimension must come first on the list of dimids. */
dimids[0] = rec_dimid;
dimids[1] = lvl_dimid;
dimids[2] = lat_dimid;
dimids[3] = lon_dimid;
/* Define the netCDF variables for the pressure and temperature
* data. */
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);
/* Assign units attributes to the netCDF variables. */
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);
/* These settings tell netcdf to write one timestep of data. (The
setting of start[0] inside the loop below tells netCDF which
timestep to write.) */
count[0] = 1;
count[1] = NLVL;
count[2] = NLAT;
count[3] = NLON;
start[1] = 0;
start[2] = 0;
start[3] = 0;
/* Write the pretend data. This will write our surface pressure and
surface temperature data. The arrays only hold one timestep worth
of data. We will just rewrite the same data for each timestep. In
a real application, the data would change between timesteps. */
for (size_t rec = 0; rec < NREC; rec++)
{
start[0] = rec;
if ((retval = nc_put_vara_float(ncid, pres_varid, start, count,
&pres_out[0][0][0])))
ERR(retval);
if ((retval = nc_put_vara_float(ncid, temp_varid, start, count,
&temp_out[0][0][0])))
ERR(retval);
}
/* Close the file. */
if ((retval = nc_close(ncid)))
ERR(retval);
printf("*** SUCCESS writing example file %s!\n", FILE_NAME);
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_UNLIMITED
#define NC_UNLIMITED
Size argument to nc_def_dim() for an unlimited dimension.
Definition netcdf.h:261
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