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/
> ===============================================================================
