NetCDF Java Library example - dump table
Requirement:
Download and import the NetCDF Library from Unidata. Version 4.1 is used in this example.
Potential problem:
If the table is too large, but the heap size (or ram size) is too small, "Array dataArray = variables.get(i).read();" will return error.
package javaapplication3;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import ucar.ma2.Array;
import ucar.nc2.Dimension;
import ucar.nc2.Variable;
import ucar.nc2.dataset.NetcdfDataset;
public class Main {
public static void main(String[] args) {
try {
// open netcdf/grib/grib2 file from argument
NetcdfDataset gid = NetcdfDataset.openDataset(args[0]);
// get all grid tables in the file
List<Variable> variables = gid.getReferencedFile().getVariables();
for (int i = 0; i < variables.size(); i++) {
if ((!variables.get(i).isMetadata()) && (!variables.get(i).getRanges().isEmpty())) {
System.out.print(variables.get(i).getName());
System.out.print(", ");
System.out.print(variables.get(i).getDataType());
System.out.print(": ");
// the range of number of the grid
System.out.print(variables.get(i).getRanges());
System.out.print(" ");
// the unit
System.out.println(variables.get(i).getUnitsString());
//the dimensions of the grid table
List<Dimension> dimensions = variables.get(i).getDimensions();
for (int j = 0; j < dimensions.size(); j++) {
try {
// the name of the dimension
System.out.print(dimensions.get(j).getName());
System.out.print(", ");
// the type of the dimension
System.out.print(gid.getReferencedFile().findVariable(dimensions.get(j).getName()).findAttribute("_CoordinateAxisType").getStringValue());
System.out.print(": ");
// the unit of the dimension
System.out.println(gid.getReferencedFile().findVariable(dimensions.get(j).getName()).getUnitsString());
} catch (Exception e) {
System.out.println();
continue;
}
}
// the data in the grid table
Array dataArray = variables.get(i).read();
// calculate the total number of dimension combination
int dimensionTotal = 1;
ArrayList<Array> dimensionsData = new ArrayList<Array>();
for (int k = 0; k < dimensions.size(); k++) {
dimensionTotal *= dimensions.get(k).getLength();
//preload the dimension value
dimensionsData.add(gid.getReferencedFile().findVariable(dimensions.get(k).getName()).read());
}
for (int j = 0; j < variables.get(i).getSize(); j++) {
System.out.print(variables.get(i).getName());
System.out.print(", ");
// for merging the dimension value
int previousDimensionTotal = dimensionTotal;
for (int k = 0; k < dimensions.size(); k++) {
previousDimensionTotal /= dimensions.get(k).getLength();
int arrayNumber = (j / previousDimensionTotal) % (dimensions.get(k).getLength());
Variable dimension = gid.getReferencedFile().findVariable(dimensions.get(k).getName());
System.out.print(dimension.findAttribute("_CoordinateAxisType").getStringValue());
System.out.print(": ");
// show the value
System.out.print(dimensionsData.get(k).getFloat(arrayNumber));
if ((k + 1) != dimensions.size()) {
System.out.print(", ");
}
}
System.out.print(" --- ");
System.out.print(" ");
// print the value
System.out.print(dataArray.getFloat(j));
System.out.println();
}
System.out.println("--------------------------------------------------");
}
}
gid.close();
} catch (IOException ex) {
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
Sample Output of reading GFS GRIB2 data from NOAA:
Absolute_vorticity, float: [0:0, 0:46, 0:10, 0:20] s-1 time, Time: hours since 2010-04-13T06:00:00Z pressure, Pressure: Pa lat, Lat: degrees_north lon, Lon: degrees_east Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 110.0 --- 5.9E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 110.5 --- 8.7E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 111.0 --- 7.8E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 111.5 --- 3.6E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 112.0 --- 3.0E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 112.5 --- 4.2E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 113.0 --- 4.6E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 113.5 --- 4.5E-5 Absolute_vorticity, Time: 12.0, Pressure: 100000.0, Lat: 20.0, Lon: 114.0 --- 4.6E-5
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