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/* This is part of the netCDF package.
Copyright 2006 University Corporation for Atmospheric Research/Unidata.
See COPYRIGHT file for conditions of use.
This example writes some surface pressure and temperatures. It is
intended to illustrate the use of the netCDF C++ API. The companion
program sfc_pres_temp_rd.cpp shows how to read the netCDF data file
created by this program.
This program is part of the netCDF tutorial:
http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-tutorial
Full documentation of the netCDF C++ API can be found at:
http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-cxx
$Id: sfc_pres_temp_wr.cpp,v 1.12 2007/01/19 12:52:13 ed Exp $
*/
#include <iostream>
#include <netcdfcpp.h>
using namespace std;
// We are writing 2D data, a 6 x 12 lat-lon grid. We will need two
// netCDF dimensions.
static const int NLAT = 6;
static const int NLON = 12;
// These are used to construct some example data.
static const float SAMPLE_PRESSURE = 900;
static const float SAMPLE_TEMP = 9.0;
static const float START_LAT = 25.0;
static const float START_LON = -125.0;
// Return this to OS if there is a failure.
static const int NC_ERR = 2;
int main(void)
{
// These will hold our pressure and temperature data.
float presOut[NLAT][NLON];
float tempOut[NLAT][NLON];
// These will hold our latitudes and longitudes.
float lats[NLAT];
float lons[NLON];
// Create some pretend data. If this wasn't an example program, we
// would have some real data to write, for example, model
// output.
for(int lat = 0; lat < NLAT; lat++)
lats[lat] = START_LAT + 5. * lat;
for(int lon = 0; lon < NLON; lon++)
lons[lon] = START_LON + 5. * lon;
for (int lat = 0; lat < NLAT; lat++)
for(int lon = 0; lon < NLON; lon++)
{
presOut[lat][lon] = SAMPLE_PRESSURE + (lon * NLAT + lat);
tempOut[lat][lon] = SAMPLE_TEMP + .25 * (lon * NLAT + lat);
}
// Change the error behavior of the netCDF C++ API by creating an
// NcError object. Until it is destroyed, this NcError object will
// ensure that the netCDF C++ API silently returns error codes
// on any failure, and leaves any other error handling to the
// calling program. In the case of this example, we just exit with
// an NC_ERR error code.
NcError err(NcError::silent_nonfatal);
// Create the file. The Replace parameter tells netCDF to overwrite
// this file, if it already exists.
NcFile dataFile("sfc_pres_temp.nc", NcFile::Replace);
// Check to see if the file was created.
if(!dataFile.is_valid())
return NC_ERR;
// Define the dimensions. NetCDF will hand back an ncDim object for
// each.
NcDim *latDim, *lonDim;
if (!(latDim = dataFile.add_dim("latitude", NLAT)))
return NC_ERR;
if (!(lonDim = dataFile.add_dim("longitude", NLON)))
return NC_ERR;
// 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."
NcVar *latVar, *lonVar;
if (!(latVar = dataFile.add_var("latitude", ncFloat, latDim)))
return NC_ERR;
if (!(lonVar = dataFile.add_var("longitude", ncFloat, lonDim)))
return NC_ERR;
// Define units attributes for coordinate vars. This attaches a
// text attribute to each of the coordinate variables, containing
// the units.
if (!lonVar->add_att("units", "degrees_east"))
return NC_ERR;
if (!latVar->add_att("units", "degrees_north"))
return NC_ERR;
// Define the netCDF data variables.
NcVar *presVar, *tempVar;
if (!(presVar = dataFile.add_var("pressure", ncFloat, latDim, lonDim)))
return NC_ERR;
if (!(tempVar = dataFile.add_var("temperature", ncFloat, latDim, lonDim)))
return NC_ERR;
// Define units attributes for variables.
if (!presVar->add_att("units", "hPa"))
return NC_ERR;
if (!tempVar->add_att("units", "celsius"))
return NC_ERR;
// Write the coordinate variable data. This will put the latitudes
// and longitudes of our data grid into the netCDF file.
if (!latVar->put(lats, NLAT))
return NC_ERR;
if (!lonVar->put(lons, NLON))
return NC_ERR;
// 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, and below we write them
// each in one step.
if (!presVar->put(&presOut[0][0], NLAT, NLON))
return NC_ERR;
if (!tempVar->put(&tempOut[0][0], NLAT, NLON))
return NC_ERR;
// The file is automatically closed by the destructor. This frees
// up any internal netCDF resources associated with the file, and
// flushes any buffers.
cout << "*** SUCCESS writing example file sfc_pres_temp.nc!" << endl;
return 0;
}
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