1 /* This is part of the netCDF package.
2 Copyright 2006 University Corporation for Atmospheric Research/Unidata.
3 See COPYRIGHT file for conditions of use.
4
5 This is a very simple example which writes a 2D array of
6 sample data. To handle this in netCDF we create two shared
7 dimensions, "X" and "Y", and a netCDF variable, called "data".
8
9 This example demonstrates the netCDF C++ API. This is part of the
10 netCDF tutorial:
11 http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-tutorial
12
13 Full documentation of the netCDF C++ API can be found at:
14 http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-cxx
15
16 $Id: sfc_pres_temp_wr.cpp,v 1.6 2010/02/11 22:36:42 russ Exp $
17 */
18
19 #include <iostream>
20 #include <netcdf>
21 using namespace std;
22 using namespace netCDF;
23 using namespace netCDF::exceptions;
24
25 // This is the name of the data file we will create.
26 #define FILE_NAME "sfc_pres_temp.nc"
27
28 // We are writing 2D data, a 6 x 12 lat-lon grid. We will need two
29 // netCDF dimensions.
30 static const int NDIMS = 2;
31 static const int NLAT = 6;
32 static const int NLON = 12;
33
34 // Names of things.
35 string PRES_NAME = "pressure";
36 string TEMP_NAME = "temperature";
37 string UNITS = "units";
38 string DEGREES_EAST = "degrees_east";
39 string DEGREES_NORTH = "degrees_north";
40 string LAT_NAME = "latitude";
41 string LON_NAME ="longitude";
42
43 // These are used to construct some example data.
44 #define SAMPLE_PRESSURE 900
45 #define SAMPLE_TEMP 9.0
46 #define START_LAT 25.0
47 #define START_LON -125.0
48
49 // Return this to OS if there is a failure.
50 #define NC_ERR 2
51
main(void)52 int main(void)
53 {
54 // We will write surface temperature and pressure fields.
55 float presOut[NLAT][NLON];
56 float tempOut[NLAT][NLON];
57 float lats[NLAT];
58 float lons[NLON];
59
60 // In addition to the latitude and longitude dimensions, we will
61 // also create latitude and longitude netCDF variables which will
62 // hold the actual latitudes and longitudes. Since they hold data
63 // about the coordinate system, the netCDF term for these is:
64 // "coordinate variables."
65 for(int lat = 0;lat < NLAT; lat++)
66 lats[lat] = START_LAT + 5.*lat;
67
68 for(int lon = 0; lon < NLON; lon++)
69 lons[lon] = START_LON + 5.*lon;
70
71 // Create some pretend data. If this wasn't an example program, we
72 // would have some real data to write, for example, model
73 // output.
74 for (int lat = 0; lat < NLAT; lat++)
75 for(int lon = 0;lon < NLON; lon++)
76 {
77 presOut[lat][lon] = SAMPLE_PRESSURE + (lon * NLAT + lat);
78 tempOut[lat][lon] = SAMPLE_TEMP + .25 * (lon * NLAT +lat);
79 }
80
81 try
82 {
83
84 // Create the file. The Replace parameter tells netCDF to overwrite
85 // this file, if it already exists.
86 NcFile sfc(FILE_NAME, NcFile::replace);
87
88 // Define the dimensions. NetCDF will hand back an ncDim object for
89 // each.
90 NcDim latDim = sfc.addDim(LAT_NAME, NLAT);
91 NcDim lonDim = sfc.addDim(LON_NAME, NLON);
92
93 // Define coordinate netCDF variables. They will hold the
94 // coordinate information, that is, the latitudes and
95 // longitudes. An pointer to a NcVar object is returned for
96 // each.
97 NcVar latVar = sfc.addVar(LAT_NAME, ncFloat, latDim);//creates variable
98 NcVar lonVar = sfc.addVar(LON_NAME, ncFloat, lonDim);
99
100 // Write the coordinate variable data. This will put the latitudes
101 // and longitudes of our data grid into the netCDF file.
102 latVar.putVar(lats);
103 lonVar.putVar(lons);
104
105 // Define units attributes for coordinate vars. This attaches a
106 // text attribute to each of the coordinate variables, containing
107 // the units. Note that we are not writing a trailing NULL, just
108 // "units", because the reading program may be fortran which does
109 // not use null-terminated strings. In general it is up to the
110 // reading C program to ensure that it puts null-terminators on
111 // strings where necessary.
112 lonVar.putAtt(UNITS,DEGREES_EAST);
113 latVar.putAtt(UNITS,DEGREES_NORTH);
114
115 // Define the netCDF data variables.
116 vector<NcDim> dims;
117 dims.push_back(latDim);
118 dims.push_back(lonDim);
119 NcVar presVar = sfc.addVar(PRES_NAME, ncFloat, dims);
120 NcVar tempVar = sfc.addVar(TEMP_NAME, ncFloat, dims);
121
122 // Define units attributes for vars.
123 presVar.putAtt(UNITS,"hPa");
124 tempVar.putAtt(UNITS,"celsius");
125
126 // Write the pretend data. This will write our surface pressure and
127 // surface temperature data. The arrays of data are the same size
128 // as the netCDF variables we have defined.
129 presVar.putVar(presOut);
130 tempVar.putVar(tempOut);
131
132 // The file is automatically closed by the destructor. This frees
133 // up any internal netCDF resources associated with the file, and
134 // flushes any buffers.
135
136 //cout << "*** SUCCESS writing example file " << FILE_NAME << "!" << endl;
137 return 0;
138 }
139 catch(NcException& e)
140 {
141 e.what();
142 return NC_ERR;
143 }
144 }
145