在真机调试时，手机放着不动，经纬度也一直在变化，甚至前后偏移距离达到30~40米

getAuth(){
    const that = this;
    wx.getSetting({
        success(res) {
          console.log("get auth success: ", res);
          // 如果没有拿到scope.userLocationBackground授权，提示
          if (!res.authSetting['scope.userLocationBackground']) {
              wx.authorize({
                  scope: 'scope.userLocationBackground',
                  success() {
                      // 用户已经同意，调用wx.startLocationUpdateBackground
                      wx.startLocationUpdateBackground({
                          success(res) {
                              // 成功开启后台定位, 调用实时位置变更
                              that.openLocaionListener()
                          },
                          fail(err) {
                            console.log("error001", err);
                            that.getLocationWithoutListener();
                          }
                      })
                  },
                  fail(err) {
                    console.log("error002", err);
                    that.getLocationWithoutListener();
                  },
              })
          } else {
              // 已经拿到scope.userLocationBackground授权调用
              wx.startLocationUpdateBackground({
                  success(res) {
                      // 成功开启后台定位,
                      that.openLocaionListener()
                  },
                  fail(err) {
                    console.log("startLocationUpdateBackground fail", err);
                  }
              })
          }
        }
    })
  },

openLocaionListener: function(){
    console.log("openLocaionListener");
    wx.onLocationChange(this._locationChangeFn) // 开始监听位置变化
  },