grib/src/main/java/ucar/nc2/grib/collection/GribCdmIndex.java
private static File makeTopIndexFileFromConfig(FeatureCollectionConfig config) {
    Formatter errlog = new Formatter();
    CollectionSpecParser specp = config.getCollectionSpecParser(errlog);

    String name = StringUtil2.replace(config.collectionName, '\\', "/");
    // String cname = DirectoryCollection.makeCollectionName(name, Paths.get(specp.getRootDir()));

    return makeIndexFile(name, new File(specp.getRootDir()));
  }
private static File makeTopIndexFileFromConfig(FeatureCollectionConfig config) {
    Formatter errlog = new Formatter();
    CollectionSpecParser specp = config.getCollectionSpecParser(errlog);

    String name = StringUtil2.replace(config.collectionName, '\\', "/");
    // String cname = DirectoryCollection.makeCollectionName(name, Paths.get(specp.getRootDir()));

    return makeIndexFile(name, new File(specp.getRootDir()));
  }
This is only used for the top level GribCollection.

@param config use this FeatureCollectionConfig
@return index File