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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Java NetCDF Folks, We have recently begun generating global 1/8 degree GRIB files using NCEP's grid 174 definition (http://www.nco.ncep.noaa.gov/pmb/docs/on388/tableb.html#GRID174). Following that definition, we are setting the value of scanMode to 64, which per GRIB2 Table 3.4 indicates "points scan in the +j direction", and so filling the data arrays from south to north. However, the java-netCDF package (v4.5) does not seem to handle the scanMode flag properly, and consequently our grids appear flipped on display. Meanwhile, I understand that NCL does handle the data mapping correctly, from which we conclude that java-netCDF is has a problem with this grid definition. As a work-around, we will set scanMode to 0 and write from north to south, which will fix the problem for us. But, we'd also hope to have the tools work correctly, too so that we can use the NCEP's grid as specified -- which admittedly is strange in that it list the corner lons from north to south. I've posted a sample GRIB2 file and resulting flipped image here: ftp://aftp.fsl.noaa.gov/divisions/its/bob/grid174_scanmode_64_example.grb2 ftp://aftp.fsl.noaa.gov/divisions/its/bob/flipped_174grid.jpg FWIW, here is the output from the (v4.3) Grib2Dump utility on that data file: Header : GRIB2 Discipline : 0 Meteorological products GRIB Edition : 2 GRIB length : 2808735 Originating Center : 59 The NOAA Forecast Systems Laboratory Originating Sub-Center : 0 Significance of Reference Time : 1 Start of forecast Reference Time : 2015-01-08T00:00:00Z Product Status : 0 Operational products Product Type : 1 Forecast products Number of data points : 4147200 Grid Name : 0 Latitude_Longitude Grid Shape: 0 Earth spherical with radius = 6,367,470 m Number of points along parallel: 2880 Number of points along meridian: 1440 Basic angle : 0 Subdivisions of basic angle: 0 Latitude of first grid point : 89.938 Longitude of first grid point : 0.062 Resolution & Component flags : 48 Winds : True Latitude of last grid point : -89.938 Longitude of last grid point : 359.938 i direction increment : 0.125 j direction increment : 0.125 Grid Units : degrees Scanning mode : 64 Product Definition : 0 Analysis/forecast at horizontal level/layer at a point in time Parameter Category : 0 Temperature Parameter Name : 0 Temperature Parameter Units : K Generating Process Type : 2 Forecast ForecastTime : 240 First Surface Type : 1 Ground or water surface First Surface value : 0.0 Second Surface Type : 255 Missing Second Surface value : 0.0 Thanks for any insights on this issue! Bob Lipschutz NOAA/ESRL/Global Systems Division IT Services/Data Services Group
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