private GribCollectionProto.Variable writeVariableProto(Grib2Rectilyser.VariableBag vb)
      throws IOException {
    GribCollectionProto.Variable.Builder b = GribCollectionProto.Variable.newBuilder();

    b.setDiscipline(vb.first.getDiscipline());
    Grib2Pds pds = vb.first.getPDS();
    b.setCategory(pds.getParameterCategory());
    b.setParameter(pds.getParameterNumber());
    b.setLevelType(pds.getLevelType1());
    b.setIsLayer(Grib2Utils.isLayer(vb.first));
    b.setIntervalType(pds.getStatisticalProcessType());
    b.setCdmHash(vb.first.cdmVariableHash(0));
    b.setRecordsPos(vb.pos);
    b.setRecordsLen(vb.length);
    b.setTimeIdx(vb.timeCoordIndex);
    if (vb.vertCoordIndex >= 0) b.setVertIdx(vb.vertCoordIndex);
    if (vb.ensCoordIndex >= 0) b.setEnsIdx(vb.ensCoordIndex);

    if (pds.isEnsembleDerived()) {
      Grib2Pds.PdsEnsembleDerived pdsDerived = (Grib2Pds.PdsEnsembleDerived) pds;
      b.setEnsDerivedType(pdsDerived.getDerivedForecastType()); // derived type (table 4.7)
    }

    if (pds.isProbability()) {
      Grib2Pds.PdsProbability pdsProb = (Grib2Pds.PdsProbability) pds;
      b.setProbabilityName(pdsProb.getProbabilityName());
      b.setProbabilityType(pdsProb.getProbabilityType());
    }

    return b.build();
  }
  protected GribCollection.VariableIndex readVariable(
      GribCollectionProto.Variable pv, GribCollection.GroupHcs group) {
    int discipline = pv.getDiscipline();
    int category = pv.getCategory();
    int param = pv.getParameter();
    int levelType = pv.getLevelType();
    int intvType = pv.getIntervalType();
    boolean isLayer = pv.getIsLayer();
    int ensDerivedType = pv.getEnsDerivedType();
    int probType = pv.getProbabilityType();
    String probabilityName = pv.getProbabilityName();
    int cdmHash = pv.getCdmHash();
    long recordsPos = pv.getRecordsPos();
    int recordsLen = pv.getRecordsLen();
    int timeIdx = pv.getTimeIdx();
    int vertIdx = pv.getVertIdx();
    int ensIdx = pv.getEnsIdx();
    int tableVersion = pv.getTableVersion();

    return gc.makeVariableIndex(
        group,
        tableVersion,
        discipline,
        category,
        param,
        levelType,
        isLayer,
        intvType,
        ensDerivedType,
        probType,
        probabilityName,
        cdmHash,
        timeIdx,
        vertIdx,
        ensIdx,
        recordsPos,
        recordsLen);
  }