message: merge to single element
diff: for (let i = 0; i < byDistance.length; i++) {
  let other = byDistance[i].el;
  if (other.pointId in this.merged) continue;
  + if (other.merged && other.merged.length > 0) {
  + this.mergeIndexElements(other, el);
  + } else {
  this.mergeIndexElements(el, other);
  + }
  return;
  }
  });
  