On Tue, 29 Sep 2009, Esteban Wagner wrote:
Hi,
I have a grb2 file containing global Primary_wave_direction forecasts. I would
like to read the
values it contains.
By the moment I was able to read the file and obtain a GridDataset using the
following code:
------------
(NetCDF:Version 4.0.16; Grib:Version 6.0.16)
final File file = new File("src/test/resources/multi_1.glo_30m.DIRPW.grb2");
final GridDataset gridDataSet = GridDataset.open(file.getAbsolutePath());
----------
the file can be downloaded from:
ftp://polar.ncep.noaa.gov/pub/waves/develop/multi_1.latest_run/multi_1.glo_30m.DIRPW.grb2
----------
Now I would like if someone can tell me which are the methods from gridDataSet
I should use in order
to obtain the different forecast values of the Primary_wave_direction for a
given grid point.
Thanks,
Regards.
Esteban.
Esteban,
I'll reference the JavaDocs first:
http://www.unidata.ucar.edu/software/netcdf-java/v4.1/javadoc/ucar/nc2/dt/GridDataset.html
http://www.unidata.ucar.edu/software/netcdf-java/v4.1/javadoc/ucar/nc2/dt/GridDatatype.html
http://www.unidata.ucar.edu/software/netcdf-java/v4.1/javadoc/ucar/nc2/dt/GridCoordSystem.html
I'm assuming by grid point you mean Lat/Lon
One needs to be at the GridCoordSystem level to be able to convert the
Lat/Lon point into indices. Then use the indices information in the
GridDatatype readDatSlice routine to get the value. Here's a short sample
program.
public class GetDataFromLatLon {
public static void main(String[] args) {
try {
final File file = new File("C:/data/grib/multi_1.glo_30m.DIRPW.grb2");
final GridDataset gridDataSet =
GridDataset.open(file.getAbsolutePath());
GridDatatype pwd = gridDataSet.findGridDatatype(
"Primary_wave_direction");
System.out.println( pwd.getInfo());
GridCoordSystem pwdGcs = pwd.getCoordinateSystem();
int[] result = null;
// Get index value for Lat 30.0 and Lon 179
int[] idx = pwdGcs.findXYindexFromLatLon( 30.0, 179.0, result );
//int[] idx = pwdGcs.findXYindexFromLatLon( 90.0, 0.0, result );
// Extract data value for time 0, no Vert index, Lat index, Lon index
Array data = pwd.readDataSlice( 0, -1, idx[1], idx[0]);
// Another option: read all data values for timeIndex = 0
//Array data = pwd.readVolumeData( 0 );
IndexIterator iter = data.getIndexIterator();
while(iter.hasNext()) {
float val = iter.getFloatNext();
System.out.println( "Primary_wave_direction = "+ val);
}
System.out.println( "Success");
} catch (Exception exc) {
exc.printStackTrace();
}
}
}
===============================================================================
Robb Kambic Unidata Program Center
Software Engineer III Univ. Corp for Atmospheric Research
rkambic@xxxxxxxxxxxxxxxx WWW: http://www.unidata.ucar.edu/
===============================================================================
