On 1/27/2012 2:14 AM, Pablo Rozas Larraondo wrote:
Good morning,
I've recently moved to NetCDF Java API from the ECMWF Grib API because
I have to work with Lambert projection Gribs and those are not fully
developed yet.
I've succeeded in opening and reading Grib1 files, but I'm having
problems trying to find out how to access data through lat lon
coordinates. In the ECMWF API there is a function called
grib_find_nearest(gid, lat,lon) in which you give a geocoordinate
point and the function returns the value of the closest, or the four
closest grid points.
Using the NetCDF API I can access the _CoordinateAxisType Attributes
of the grib file which are GeoX and GeoY expressed in Km, but I wonder
if there is a function for accessing values or translating points into
geographic coordinates.
Thank you very much for your help,
Pablo Rozas
AEMet Analyst Forecaster
Santander, Spain
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Hi Pablo:
You can open the file as a GridDataset, then use
GridCoordSystem.findXYindexFromLatLon() to figure out
which index is at that lat,lon, eg:
// open the dataset, find the variable and its coordinate system
GridDataset gds = ucar.nc2.dt.grid.GridDataset.open(location);
GridDatatype grid = gds.findGridDatatype( "myVariableName");
GridCoordSystem gcs = grid.getCoordinateSystem();
double lat = 8.0;
double lon = 21.0;
// find the x,y index for a specific lat/lon position
int[] xy = gcs.findXYindexFromLatLon(lat, lon, null); // xy[0] = x,
xy[1] = y
// read the data at that lat, lon and the first time and z level (if
any)
Array data = grid.readDataSlice(0, 0, xy[1], xy[0]); // note order
is t, z, y, x
double val = data.getDouble(0); // we know its a scalar
System.out.printf("Value at %f %f == %f%n", lat, lon, val);
John
