 0 });
    const emitArc = useCallback(({ lat: endLat, lng: endLng }) => {
      const { lat: startLat, lng: startLng } = prevCoords.current;
      prevCoords.current = { lat: endLat, lng: endLng };

      // add and remove arc after 1 cycle
      const arc = { startLat, startLng, endLat, endLng };
      setArcsData(curArcsData => [...curArcsData, arc]);
      setTimeout(() => setArcsData(curArcsData => curArcsData.filter(d => d !== arc)), FLIGHT_TIME * 2);

      // add and remove start rings
      const s