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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 is a very simple example which writes a 2D array of
sample data. To handle this in netCDF we create two shared
dimensions, "X" and "Y", and a netCDF variable, called "data".
This example demonstrates the netCDF C++ API. This 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 1.6 2010/02/11 22:36:42 russ Exp $
*/
#include <iostream>
#include <netcdf>
using namespace std;
using namespace netCDF;
using namespace netCDF::exceptions;
// 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.
static const int NDIMS = 2;
static const int NLAT = 6;
static const int NLON = 12;
// Names of things.
string PRES_NAME = "pressure";
string TEMP_NAME = "temperature";
string UNITS = "units";
string DEGREES_EAST = "degrees_east";
string DEGREES_NORTH = "degrees_north";
string LAT_NAME = "latitude";
string LON_NAME ="longitude";
// These are used to construct some example data.
#define SAMPLE_PRESSURE 900
#define SAMPLE_TEMP 9.0
#define START_LAT 25.0
#define START_LON -125.0
// Return this to OS if there is a failure.
#define NC_ERR 2
int main(void)
{
// We will write surface temperature and pressure fields.
float presOut[NLAT][NLON];
float tempOut[NLAT][NLON];
float lats[NLAT];
float lons[NLON];
// 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."
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;
// 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++)
for(int lon = 0;lon < NLON; lon++)
{
presOut[lat][lon] = SAMPLE_PRESSURE + (lon * NLAT + lat);
tempOut[lat][lon] = SAMPLE_TEMP + .25 * (lon * NLAT +lat);
}
try
{
// Create the file. The Replace parameter tells netCDF to overwrite
// this file, if it already exists.
NcFile sfc(FILE_NAME, NcFile::replace);
// Define the dimensions. NetCDF will hand back an ncDim object for
// each.
NcDim latDim = sfc.addDim(LAT_NAME, NLAT);
NcDim lonDim = sfc.addDim(LON_NAME, NLON);
// Define coordinate netCDF variables. They will hold the
// coordinate information, that is, the latitudes and
// longitudes. An pointer to a NcVar object is returned for
// each.
NcVar latVar = sfc.addVar(LAT_NAME, ncFloat, latDim);//creates variable
NcVar lonVar = sfc.addVar(LON_NAME, ncFloat, lonDim);
// Write the coordinate variable data. This will put the latitudes
// and longitudes of our data grid into the netCDF file.
latVar.putVar(lats);
lonVar.putVar(lons);
// 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.
lonVar.putAtt(UNITS,DEGREES_EAST);
latVar.putAtt(UNITS,DEGREES_NORTH);
// Define the netCDF data variables.
vector<NcDim> dims;
dims.push_back(latDim);
dims.push_back(lonDim);
NcVar presVar = sfc.addVar(PRES_NAME, ncFloat, dims);
NcVar tempVar = sfc.addVar(TEMP_NAME, ncFloat, dims);
// Define units attributes for vars.
presVar.putAtt(UNITS,"hPa");
tempVar.putAtt(UNITS,"celsius");
// 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.
presVar.putVar(presOut);
tempVar.putVar(tempOut);
// 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 " << FILE_NAME << "!" << endl;
return 0;
}
catch(NcException& e)
{
e.what();
return NC_ERR;
}
}
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