我正在抓取一个显示公交车纬度和经度的 Web API。
网络服务似乎没有固定的 GPS 位置更新时间，可能需要 1 秒到最多 30 秒。
当更新时间较长时，我会得到合理的速度(10km/h~80km/h)，但当更新发生在不到 10 秒时，我会得到不真实的速度，最高可达 1000 km/h。
def haversine(lon1, lat1, lon2, lat2):
"""Calculate the distance between two points"""
lon1, lat1, lon2, lat2 = map(radians, [lon1, lat1, lon2, lat2])
dlon = lon2 - lon1
dlat = lat2 - lat1
a = sin(dlat/2)**2 + cos(lat1) * cos(lat2) * sin(dlon/2)**2
c = 2 * asin(sqrt(a))
r = 6371 # Radius of earth in kilometers. Use 3956 for miles
return c * r
def get_speed(new_lat, new_lng, cur_time):
old_lat, old_lng, old_time = buses[bus_prefix]
if (new_lat, new_lng) != (old_lat, old_lng):
distance = haversine(old_lng, old_lat, new_lng, new_lat)
speed = distance / (cur_time - old_time) * 3600
_speed = "%.1f km/h" % speed
updated_time = "%02d:%02d"%(divmod(cur_time-old_time, 60))
return _speed, updated_time
return None, None
url = 'http://api.plataforma.cittati.com.br/m3p/js/vehicles/service/22233'
buses = {}
with requests.session() as s:
while True:
response = s.get(url)
t = time.time()
content = json.loads(response.content)
for bus in content:
bus_prefix = bus['prefix']
latitude = bus['lat']
longitude = bus['lng']
if bus_prefix in buses:
speed, update_time = get_speed(latitude, longitude, t)
if speed and update_time:
print "Bus {bus_prefix} is traveling at {speed}\t" \
"Last update in: {update_time}".format(**locals())
buses[bus_prefix] = latitude, longitude, t
time.sleep(1)
也许我做错了一些数学，或者我所在城市的公交车正在赛车，但我仔细检查了所有内容，包括赛车!
这是我为了弄清楚发生了什么而进行的调试:
old_lat = -32.0916777778
new_lat = -32.0937277778
new_lng = -52.1608333333
old_lng = -52.1598611111
distance = 0.245660526035 in kms
old_time = 1436580324.66 in epoch seconds
cur_time = 1436580325.94 in epoch seconds
delta time = 1.28700017929 in seconds
speed = 687.162214861 in km/h
Bus 1145 is traveling at 687.2 km/h Last update in: 00:01
有人能发现任何错误吗？或者这是正确的方法吗？ Haversine 是适合这项工作的工具吗？
最佳答案
从您发布的url，我得到了以下输出:
[{"plate":"IUZ4600","prefix":"1310","ts":1436583122000,"lat":-32.061505555555556,"lng":-52.147172222222224,"bearing":37} ,{"plate":"ISO8600","prefix":"1145","ts":1436583099000,"lat":-32.15838333333333,"lng":-52.19098888888889,"bearing":309}]
这是一个字典列表，我假设每个字典都引用一辆公共(public)汽车，
在每个字典中，都有一个名为ts的key，它应该是每次更新的lat和long的时间戳，应将其相应的值用于计算速度，以便为您提供更准确的结果:
t = 总线["ts"]
关于python - 使用公共(public) GPS 数据计算速度，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31352752/