docs: @Override
      public boolean loadExisting() {
          if (!index.loadExisting())
              return false;
  
          if (index.getHeader(0) != MAGIC_INT)
              throw new IllegalStateException("incorrect loc2id index version");
  
          int lat = index.getHeader(1 * 4);
          int lon = index.getHeader(2 * 4);
          int checksum = index.getHeader(3 * 4);
          if (checksum != graph.getNodes())
              throw new IllegalStateException("index was created from a different graph with "
                      + checksum + ". Current nodes:" + graph.getNodes());
  
          initAlgo(lat, lon);
          return true;
      }