每20米或3秒获取一次服务位置

function getLocation() {
  if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(showPosition, showError);
  } else {
    console.log("Geolocation is not supported by this browser.");
  }
}

function showPosition(position) {
  console.log("Latitude: " + position.coords.latitude + 
            " Longitude: " + position.coords.longitude);
  // 在这里处理位置数据
}

function showError(error) {
  switch(error.code) {
    case error.PERMISSION_DENIED:
      console.log("User denied the request for Geolocation.");
      break;
    case error.POSITION_UNAVAILABLE:
      console.log("Location information is unavailable.");
      break;
    case error.TIMEOUT:
      console.log("The request to get user location timed out.");
      break;
    case error.UNKNOWN_ERROR:
      console.log("An unknown error occurred.");
      break;
  }
}

let watchId;
let lastPosition;
const distanceThreshold = 20; // 20米
const timeThreshold = 3000; // 3秒

function startTracking() {
  watchId = navigator.geolocation.watchPosition(showPosition, showError, {
    enableHighAccuracy: true,
    timeout: timeThreshold,
    maximumAge: 0
  });

  setInterval(getLocation, timeThreshold);
}

function stopTracking() {
  navigator.geolocation.clearWatch(watchId);
}

function showPosition(position) {
  if (lastPosition) {
    const distance = calculateDistance(lastPosition, position.coords);
    if (distance >= distanceThreshold) {
      console.log("Distance threshold reached. New position:");
      console.log("Latitude: " + position.coords.latitude + 
                " Longitude: " + position.coords.longitude);
    }
  }
  lastPosition = position.coords;
}

function calculateDistance(pos1, pos2) {
  const R = 6371e3; // metres
  const φ1 = pos1.latitude * Math.PI / 180; // φ, λ in radians
  const φ2 = pos2.latitude * Math.PI / 180;
  const Δφ = (pos2.latitude - pos1.latitude) * Math.PI / 180;
  const Δλ = (pos2.longitude - pos1.longitude) * Math.PI / 180;

  const a =
    Math.sin(Δφ / 2) * Math.sin(Δφ / 2) +
    Math.cos(φ1) * Math.cos(φ2) *
    Math.sin(Δλ / 2) * Math.sin(Δλ / 2);
  const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));

  const d = R * c; // in metres
  return d;
}

startTracking(); // 开始跟踪
// stopTracking(); // 停止跟踪