_onPoll() {
    const planeCount = this.planes.size();
    // Plane count will change much less often than position or hits;
    // don't even bother throttling to rerender the same information
    // if there are no changes
    if (this._lastPlaneCount !== planeCount) {
      this.update(this._planesToString(planeCount), planeCount > 0, true);
    }
    this._lastPlaneCount = planeCount;
  }
Polling callback while enabled, used to fetch and orchestrate
plane rendering.