NetCDF与Java:如何使用变量名称查找从GridDataset获取GeoGrid

Question

我有Java代码，它通过变量名从GeoGrid GridDataset中获取一个NetCDF对象。它通常正常工作，但对于输入NetCDF文件，我目前需要处理的输入代码在运行此代码时出错，因为没有找到GeoGrid，即使您可以使用其他工具(如ncdump和/或在使用调试器遍历代码时看到NetCDF dataset中的变量)。

我假设NetCDF文件本身一定存在一些东西，它阻止通过查找变量名来获取变量的网格。当我查看NetCDF文件时，我可以看到变量，它以Geo2D类型显示。文件的ncdump -h输出如下：

File "prism_nidis_pet.nc"
Dataset type: NetCDF-3/CDM
 
netcdf file:/C:/home/prism/prism_nidis_pet.nc {
  dimensions:
    lon = 1405;
    lat = 621;
    time = UNLIMITED;   // (1457 currently
  variables:
    int time(time=1457);
      :long_name = "time";
      :standard_name = "time";
      :units = "days since 1800-1-1 00:00:00";
      :calendar = "gregorian";

    float lon(lon=1405);
      :long_name = "longitude";
      :standard_name = "longitude";
      :units = "degrees_north";

    float lat(lat=621);
      :long_name = "latitude";
      :standard_name = "latitude";
      :units = "degrees_west";

    float pet(time=1457, lon=1405, lat=621);
      :calibration_start_year_month = "full";
      :calibration_end_year_month = "full";
      :_FillValue = -999.9f; // float
      :missing_value = -999.9f; // float
      :valid_min = 0.0f; // float
      :valid_max = 3.4028235E38f; // float
      :units = "millimeters";
      :cell_methods = "time: potential evapotranspiration estimate, Thornthwaite equation";
      :long_name = "Potential evapotranspiration estimate, Thornthwaite equation";
      :standard_name = "Potential evapotranspiration estimate, Thornthwaite equation";

  // global attributes:
  :date_created = "2016-06-23  11:52:37";
  :date_modified = "2016-06-23  11:52:37";
  :standard_name_vocabulary = "CF Standard Name Table (v26, 08 November 2013)";
  :Conventions = "1.6";
  :geospatial_lon_min = -125.0f; // float
  :geospatial_lon_max = -66.5f; // float
  :geospatial_lat_min = 24.083334f; // float
  :geospatial_lat_max = 49.916668f; // float
}

上面描述的文件中有什么会阻止与名为“GeoGrid”的变量关联的吗？

下面是使用上述文件作为输入时失败的代码。

    private GeoGrid getGrid(final String netcdfFile,
                            final String variableName)
        throws IOException
    {
        // open the NetCDF data set
        GridDataset gridDataset = GridDataset.open(netcdfFile);

        // verify that we opened the GridDataset
        if (gridDataset == null)
        {
            String errorMessage = "Error opening the NetCDF data set using the file \'" + netcdfFile + "\'";
            logger.error(errorMessage);
            throw new RuntimeException(errorMessage);
        }

        // THIS IS WHERE THE PROBLEM OCCURS
        // get the grid based on the associated variable name
        GeoGrid geoGrid = gridDataset.findGridByShortName(variableName);

        // verify that we found the GeoGrid
        if (geoGrid == null)
        {
            String errorMessage = "Error finding the NetCDF grid from the NetCDF file \'" + netcdfFile + "\' using the variable name \'" + variableName + "\'";
            logger.error(errorMessage);
            throw new RuntimeException(errorMessage);
        }

        // more code omitted...
    }

当上面的代码运行并失败时，参数是NetCDF文件名和"pet“，这是NetCDF中的变量名，我们正试图获得相应的网格。

这里出什么问题了？

Answer 1

经度和纬度变量的单位看起来很糟糕，这可能会扰乱您显然正在调用的netCDF库代码。你的CDL片段说龙有单位"degrees_north“和lat "degrees_west”。那应该是龙"degrees_east“和"degrees_north”。