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Dear All, I would like to write a netCDF4 file in Java based on https://www.unidata.ucar.edu/software/thredds/current/netcdf-java/tutorial/NetcdfWriting.html. I have a lot of variables and I would like to select just some and write only them to netcdf file. I tried to solve this by the the following way: public class JavaDB { public static Variable time; public static Variable cloud_1st; public static Variable cloud_2nd; public static Variable cloud_3th; public static Variable cloud_4th; public static Variable cloud_5th; public static Variable Layer_1st; public static Variable Layer_2nd; public static Variable Layer_3th; public static Variable Layer_4th; public static Variable Layer_5th; public static Variable CBN; public static void getDataNC(String location, ArrayList<Integer> Values) throws Exception{ String version = System.getProperty("java.version"); NetcdfFileWriter ncfile = NetcdfFileWriter.createNew(NetcdfFileWriter.Version.netcdf4, location, null); // add dimensions Dimension heightDim = ncfile.addDimension(null,"height",1539); Dimension timeDim = ncfile.addUnlimitedDimension("time"); //define variables for(int k=0; k<Values.size(); k++){ switch(Values.get(k)){ case 1: Variable time = ncfile.addVariable(null, "time", DataType.DOUBLE,"time"); time.addAttribute( new Attribute("units", "days since 1970-01-01")); break; case 2: Variable cloud_1st = ncfile.addVariable(null,"cloud_1st", DataType.INT,"time"); cloud_1st.addAttribute( new Attribute("long_name", "cloud amount in 1st layer1")); cloud_1st.addAttribute( new Attribute("units", "octa")); cloud_1st.addAttribute(new Attribute("_FillValue",-9999)); cloud_1st.addAttribute(new Attribute("Vertical Visibility",9)); cloud_1st.addAttribute(new Attribute("No enough data",99)); break; case 3: Variable cloud_2nd = ncfile.addVariable(null,"cloud_2nd", DataType.INT,"time"); cloud_2nd.addAttribute( new Attribute("long_name", "cloud amount in 2nd layer")); cloud_2nd.addAttribute( new Attribute("units", "octa")); cloud_2nd.addAttribute(new Attribute("_FillValue",-9999)); cloud_2nd.addAttribute(new Attribute("Vertical Visibility",9)); cloud_2nd.addAttribute(new Attribute("No enough data",99)); break; case 4: Variable cloud_3th = ncfile.addVariable(null,"cloud_3th", DataType.INT,"time"); cloud_3th.addAttribute( new Attribute("long_name", "cloud amount in 3th layer")); cloud_3th.addAttribute( new Attribute("units", "octa")); cloud_3th.addAttribute(new Attribute("_FillValue",-9999)); cloud_3th.addAttribute(new Attribute("Vertical Visibility",9)); cloud_3th.addAttribute(new Attribute("No enough data",99)); break; case 5: Variable cloud_4th = ncfile.addVariable(null, "cloud_4th", DataType.INT, "time"); cloud_4th.addAttribute( new Attribute("long_name", "cloud amount in 4th layer")); cloud_4th.addAttribute( new Attribute("units", "octa")); cloud_4th.addAttribute(new Attribute("_FillValue",-9999)); cloud_4th.addAttribute(new Attribute("Vertical Visibility", 9)); cloud_4th.addAttribute(new Attribute("No enough data",99)); break; case 6: Variable cloud_5th = ncfile.addVariable(null, "cloud_5th", DataType.INT, "time"); cloud_5th.addAttribute( new Attribute("long_name", "cloud amount in 5th layer")); cloud_5th.addAttribute( new Attribute("units", "octa")); cloud_5th.addAttribute(new Attribute("_FillValue",-9999)); cloud_5th.addAttribute(new Attribute("Vertical Visibility",9)); cloud_5th.addAttribute(new Attribute("no enough data",99)); break; case 7: Variable Layer_1st = ncfile.addVariable(null,"Layer_1st",DataType.INT,"time"); Layer_1st.addAttribute(new Attribute("long_name", "1st cloud layer height")); Layer_1st.addAttribute(new Attribute("units","meter")); Layer_1st.addAttribute(new Attribute("_FillValue",-9999)); break; case 8: Variable Layer_2nd = ncfile.addVariable(null,"Layer_2nd",DataType.INT,"time"); Layer_2nd.addAttribute(new Attribute("long_name", "2nd cloud layer height")); Layer_2nd.addAttribute(new Attribute("units","meter")); Layer_2nd.addAttribute(new Attribute("_FillValue",-9999)); break; case 9: Variable Layer_3th = ncfile.addVariable(null,"Layer_3th",DataType.INT,"time"); Layer_3th.addAttribute(new Attribute("long_name", "3th cloud layer height")); Layer_3th.addAttribute(new Attribute("units","meter")); Layer_3th.addAttribute(new Attribute("_FillValue",-9999)); break; case 10: Variable Layer_4th = ncfile.addVariable(null,"Layer_4th",DataType.INT,"time"); Layer_4th.addAttribute(new Attribute("long_name", "4th cloud layer height")); Layer_4th.addAttribute(new Attribute("units","meter")); Layer_4th.addAttribute(new Attribute("_FillValue",-9999)); break; case 11: Variable Layer_5th = ncfile.addVariable(null,"Layer_5th",DataType.INT,"time"); Layer_5th.addAttribute(new Attribute("long_name", "5th cloud layer height")); Layer_5th.addAttribute(new Attribute("units","meter")); Layer_5th.addAttribute(new Attribute("_FillValue",-9999)); break; case 12: Variable CBN = ncfile.addVariable(null,"CBN",DataType.INT,"time"); CBN.addAttribute(new Attribute("long_name","cloud base number")); CBN.addAttribute(new Attribute("units", "number")); CBN.addAttribute(new Attribute("no significant backscatter",0)); CBN.addAttribute(new Attribute("obscuration but no cloud",4)); CBN.addAttribute(new Attribute("transparent obscuration",5)); CBN.addAttribute(new Attribute("_FillValue",-9)); break; } } ncfile.create(); try{ ArrayDouble.D1 timeData = new ArrayDouble.D1(countLinesResult); ArrayInt.D1 cloudL1Data = new ArrayInt.D1(countLinesResult); Index ima = cloudL1Data.getIndex(); ArrayInt.D1 cloudL2Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cloudL3Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cloudL4Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cloudL5Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cLayer1Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cLayer2Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cLayer3Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cLayer4Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 cLayer5Data = new ArrayInt.D1(countLinesResult); ArrayInt.D1 CBNData = new ArrayInt.D1(countLinesResult); for (int timeIdx = 0; timeIdx < countLinesResult;timeIdx++){ for(int k=0; k<Values.size(); k++){ // System.out.println(Values.get(k)); if(Values.get(k)==1){ timeData.setDouble(timeIdx,tdate.get(timeIdx));} if(Values.get(k)==2){ cloudL1Data.setInt(ima.set(timeIdx), cloud_layer_1st.get(timeIdx));} if(Values.get(k)==3){ cloudL2Data.setInt(ima.set(timeIdx), cloud_layer_2nd.get(timeIdx));} if(Values.get(k)==4){ cloudL3Data.setInt(ima.set(timeIdx), cloud_layer_3th.get(timeIdx));} if(Values.get(k)==5){ cloudL4Data.setInt(ima.set(timeIdx), cloud_layer_4th.get(timeIdx));} if(Values.get(k)==6){ cloudL5Data.setInt(ima.set(timeIdx), cloud_layer_5th.get(timeIdx));} if(Values.get(k)==7){ cLayer1Data.setInt(ima.set(timeIdx), LayerC_1st.get(timeIdx));} if(Values.get(k)==8){ cLayer2Data.setInt(ima.set(timeIdx), LayerC_2nd.get(timeIdx));} if(Values.get(k)==9){ cLayer3Data.setInt(ima.set(timeIdx), LayerC_3th.get(timeIdx));} if(Values.get(k)==10){ cLayer4Data.setInt(ima.set(timeIdx), LayerC_4th.get(timeIdx));} if(Values.get(k)==11){ cLayer5Data.setInt(ima.set(timeIdx), LayerC_5th.get(timeIdx));} if(Values.get(k)==12){ CBNData.setInt(ima.set(timeIdx),nbcb.get(timeIdx));} } } // write the data into netCDF file for(int k=0; k<Values.size(); k++){ if(Values.get(k)==1){ ncfile.write(time, timeData);} if(Values.get(k)==2){ ncfile.write(cloud_1st, cloudL1Data);} if(Values.get(k)==3){ ncfile.write(cloud_2nd, cloudL2Data);} if(Values.get(k)==4){ ncfile.write(cloud_3th, cloudL3Data);} if(Values.get(k)==5){ ncfile.write(cloud_4th, cloudL4Data);} if(Values.get(k)==6){ ncfile.write(cloud_5th, cloudL5Data);} if(Values.get(k)==7){ ncfile.write(Layer_1st, cLayer1Data);} if(Values.get(k)==8){ ncfile.write(Layer_2nd, cLayer2Data);} if(Values.get(k)==9){ ncfile.write(Layer_3th, cLayer3Data);} if(Values.get(k)==10){ ncfile.write(Layer_4th, cLayer4Data);} if(Values.get(k)==11){ ncfile.write(Layer_5th, cLayer5Data);} if(Values.get(k)==12){ ncfile.write(CBN,CBNData);} } }catch(Exception e){ e.printStackTrace();} finally{ try{ ncfile.close(); }catch(IOException ex){ ex.printStackTrace(); } } But after I run the code I get java.lang.NullPointerException at ucar.nc2.NetcdfFileWriter.write(NetcdfFileWriter.java:939). I tried to solve it with define global variables size e.g public static Variable time = new Variable(); but it is not possible. Could you please informe me how I should fix this issue? Thank you for your help in adavnce! Best regards, Beata
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