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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
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Robb, thanks for the code, it worked great!. I have a question regarding the perfomance of the reading: With the code you sent me, reading a grib2 file with 11 parameters and 31 times each for only one location takes: 80 seconds. Is there any way to improve this time? As I want to gather values for several locations, say more than 100 locations its a lot of time.(80sec * 100 = 8000 sec = 2.2 hours). * Perfomance measures were obtained with the following: * Hardware: Amd Turion 64 X2 TL-58 1.9GHz , 3Gb Ram, Windows Vista 32, 5400Rpm HD. * Grib2 file: ftp://polar.ncep.noaa.gov/pub/waves/develop/multi_1.latest_run/multi_1.glo_30m.all.grb2 * Library versions:(NetCDF:Version 4.0.16; Grib:Version 6.0.16) * Code : --------------- import java.io.File; import java.util.Date; import ucar.ma2.Array; import ucar.ma2.IndexIterator; import ucar.nc2.dt.GridCoordSystem; import ucar.nc2.dt.GridDatatype; import ucar.nc2.dt.grid.GridDataset; public class ReadLatLonFromGrib { public static void main(final String[] args) { final File file = new File( "src/test/resources/multi_1.glo_30m.all.grb2"); final float lat = 39; final float lon = 179; final long startTime = new Date().getTime(); // Read the values for the given location readValuesForLocation(file, lat, lon); final long endTime = new Date().getTime(); // Calculate reading elapsed time(seconds). final long elapsedTime = (endTime - startTime) / 1000; System.out.println("Time elapsed for reading " + parameters.values().length + " parameters, for 31 times, in one location: " + elapsedTime + " secs."); } private static enum parameters { Direction_of_swell_waves, Direction_of_wind_waves, Mean_period_of_swell_waves, Mean_period_of_wind_waves, Primary_wave_direction, Primary_wave_mean_period, Significant_height_of_combined_wind_waves_and_swell, Significant_height_of_swell_waves, Significant_height_of_wind_waves, Wind_direction_from_which_blowing, Wind_speed }; private static void readValuesForLocation(final File file, final float lat, final float lon) { System.out.println("Reading grib values for lat: " + lat + " and lon: " + lon); try { // For each parameter for (final Enum parameter : parameters.values()) { final GridDataset gridDataSet = GridDataset.open(file .getAbsolutePath()); // For each time for (int i = 0; i < 31; i++) { final GridDatatype pwd = gridDataSet .findGridDatatype(parameter.name()); final GridCoordSystem pwdGcs = pwd.getCoordinateSystem(); final int[] result = null; // Get index value for lat/lon final int[] idx = pwdGcs.findXYindexFromLatLon(lat, lon, result); // Reads values for the given (location,parameter,time) final Array data = pwd.readDataSlice(i, -1, idx[1], idx[0]); final IndexIterator iter = data.getIndexIterator(); while (iter.hasNext()) { // Obtain the value final float val = iter.getFloatNext(); } } } System.out.println("Finish reading values"); } catch (final Exception exc) { exc.printStackTrace(); } } } Thanks. Regards. Esteban. ------------------------------------------------------------------------------------------------- On Fri, Oct 2, 2009 at 4:14 PM, Robb Kambic <rkambic@xxxxxxxxxxxxxxxx> wrote: > 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/ > ===============================================================================
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