TrajectoryObsDatasetImpl.Config trajConfig = new TrajectoryObsDatasetImpl.Config();
    trajConfig.setTrajectoryDim( d);
    // Check that have variable time(time) with units that are udunits time
    Variable var = ncd.getRootGroup().findVariable( dimVarName);
    if ( var == null) return null;
    list = var.getDimensions();
    if ( list.size() != 1) return null;
    d = (Dimension) list.get(0);
    if ( ! d.getName().equals( dimName)) return null;
    String units = var.findAttribute( "units").getStringValue();
    if ( ! SimpleUnit.isCompatible( units, "km")) return null;
    trajConfig.setDimensionVar( var);
    // Check for variable latitude(time) with units of "deg".
    var = ncd.getRootGroup().findVariable( latVarName);
    if ( var == null ) return null;
    list = var.getDimensions();
    if ( list.size() != 1) return null;
    d = (Dimension) list.get(0);
    if ( ! d.getName().equals( dimName)) return null;
    units = var.findAttribute( "units").getStringValue();
    if ( ! SimpleUnit.isCompatible( units, "deg")) return null;
    trajConfig.setLatVar( var);
    // Check for variable longitude(time) with units of "deg".
    var = ncd.getRootGroup().findVariable( lonVarName);
    if ( var == null ) return null;
    list = var.getDimensions();
    if ( list.size() != 1) return null;
    d = (Dimension) list.get(0);
    if ( ! d.getName().equals( dimName)) return null;
    units = var.findAttribute( "units").getStringValue();
    if ( ! SimpleUnit.isCompatible( units, "deg")) return null;
    trajConfig.setLonVar( var);
    // Check for variable altitude(time) with units of "m".
    var = ncd.getRootGroup().findVariable( elevVarName);
    if ( var == null) return null;
    list = var.getDimensions();
    if ( list.size() != 1) return null;
    d = (Dimension) list.get(0);
    if ( ! d.getName().equals( dimName)) return null;
    units = var.findAttribute( "units").getStringValue();
    if ( ! SimpleUnit.isCompatible( units, "km")) return null;
    trajConfig.setElevVar( var);
    trajConfig.setTrajectoryId( trajId);