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162 lines
4.4 KiB
C
162 lines
4.4 KiB
C
/*! \file
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Example program for reading a 4D netCDF file
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\ingroup tutorial
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This is an example which reads some 4D pressure and temperatures. The
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data file read by this program is produced by the companion program
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pres_temp_4D_wr.c. It is intended to illustrate the use of the netCDF
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C API.
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This is part of the netCDF package. Copyright 2006-2011 University
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Corporation for Atmospheric Research/Unidata. See COPYRIGHT file for
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conditions of use. Full documentation of the netCDF can be found at
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http://www.unidata.ucar.edu/software/netcdf/docs.
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*/
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#include <stdio.h>
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#include <string.h>
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#include <netcdf.h>
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/* This is the name of the data file we will read. */
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#define FILE_NAME "pres_temp_4D.nc"
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/* We are reading 4D data, a 2 x 6 x 12 lvl-lat-lon grid, with 2
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timesteps of data. */
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#define NDIMS 4
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#define NLAT 6
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#define NLON 12
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#define LAT_NAME "latitude"
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#define LON_NAME "longitude"
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#define NREC 2
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#define REC_NAME "time"
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#define LVL_NAME "level"
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#define NLVL 2
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/* Names of things. */
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#define PRES_NAME "pressure"
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#define TEMP_NAME "temperature"
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#define UNITS "units"
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#define DEGREES_EAST "degrees_east"
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#define DEGREES_NORTH "degrees_north"
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/* These are used to calculate the values we expect to find. */
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#define SAMPLE_PRESSURE 900
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#define SAMPLE_TEMP 9.0
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#define START_LAT 25.0
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#define START_LON -125.0
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/* For the units attributes. */
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#define UNITS "units"
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#define PRES_UNITS "hPa"
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#define TEMP_UNITS "celsius"
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#define LAT_UNITS "degrees_north"
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#define LON_UNITS "degrees_east"
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#define MAX_ATT_LEN 80
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/* Handle errors by printing an error message and exiting with a
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* non-zero status. */
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#define ERR(e) {printf("Error: %s\n", nc_strerror(e)); return 2;}
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int
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main()
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{
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int ncid, pres_varid, temp_varid;
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int lat_varid, lon_varid;
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/* The start and count arrays will tell the netCDF library where to
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read our data. */
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size_t start[NDIMS], count[NDIMS];
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/* Program variables to hold the data we will read. We will only
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need enough space to hold one timestep of data; one record. */
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float pres_in[NLVL][NLAT][NLON];
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float temp_in[NLVL][NLAT][NLON];
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/* These program variables hold the latitudes and longitudes. */
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float lats[NLAT], lons[NLON];
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/* Loop indexes. */
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int lvl, lat, lon, rec, i = 0;
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/* Error handling. */
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int retval;
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/* Open the file. */
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if ((retval = nc_open(FILE_NAME, NC_NOWRITE, &ncid)))
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ERR(retval);
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/* Get the varids of the latitude and longitude coordinate
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* variables. */
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if ((retval = nc_inq_varid(ncid, LAT_NAME, &lat_varid)))
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ERR(retval);
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if ((retval = nc_inq_varid(ncid, LON_NAME, &lon_varid)))
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ERR(retval);
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/* Read the coordinate variable data. */
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if ((retval = nc_get_var_float(ncid, lat_varid, &lats[0])))
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ERR(retval);
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if ((retval = nc_get_var_float(ncid, lon_varid, &lons[0])))
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ERR(retval);
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/* Check the coordinate variable data. */
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for (lat = 0; lat < NLAT; lat++)
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if (lats[lat] != START_LAT + 5.*lat)
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return 2;
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for (lon = 0; lon < NLON; lon++)
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if (lons[lon] != START_LON + 5.*lon)
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return 2;
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/* Get the varids of the pressure and temperature netCDF
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* variables. */
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if ((retval = nc_inq_varid(ncid, PRES_NAME, &pres_varid)))
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ERR(retval);
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if ((retval = nc_inq_varid(ncid, TEMP_NAME, &temp_varid)))
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ERR(retval);
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/* Read the data. Since we know the contents of the file we know
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* that the data arrays in this program are the correct size to
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* hold one timestep. */
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count[0] = 1;
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count[1] = NLVL;
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count[2] = NLAT;
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count[3] = NLON;
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start[1] = 0;
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start[2] = 0;
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start[3] = 0;
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/* Read and check one record at a time. */
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for (rec = 0; rec < NREC; rec++)
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{
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start[0] = rec;
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if ((retval = nc_get_vara_float(ncid, pres_varid, start,
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count, &pres_in[0][0][0])))
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ERR(retval);
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if ((retval = nc_get_vara_float(ncid, temp_varid, start,
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count, &temp_in[0][0][0])))
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ERR(retval);
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/* Check the data. */
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i = 0;
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for (lvl = 0; lvl < NLVL; lvl++)
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for (lat = 0; lat < NLAT; lat++)
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for (lon = 0; lon < NLON; lon++)
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{
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if (pres_in[lvl][lat][lon] != SAMPLE_PRESSURE + i)
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return 2;
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if (temp_in[lvl][lat][lon] != SAMPLE_TEMP + i)
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return 2;
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i++;
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}
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} /* next record */
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/* Close the file. */
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if ((retval = nc_close(ncid)))
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ERR(retval);
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printf("*** SUCCESS reading example file pres_temp_4D.nc!\n");
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return 0;
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}
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