Python GPS模块:读取最新的GPS数据

Question

我一直在尝试使用python 2.6中的标准GPS (gps.py)模块。它应该充当客户端，并从运行在Ubuntu中的gpsd中读取GPS数据。

根据GPSD客户端设计网页(GPSD客户端操作)的文档，我应该能够使用下面的代码(从示例中略作修改)来获取最新的GPS读数( long是我主要感兴趣的)。

from gps import *
session = gps() # assuming gpsd running with default options on port 2947
session.stream(WATCH_ENABLE|WATCH_NEWSTYLE)
report = session.next()
print report

如果我重复使用next()，它会给出队列底部(会话启动时)的缓冲值，而不是最新的Gps读数。是否有一种方法可以使用这个库获得更多的最近值？在某种程度上，寻找流的最新价值？

有没有人有一个代码示例，使用这个库来轮询gps并得到我正在寻找的值？

这里是我想要做的：

1. 启动会话
2. 等待用户在代码中调用gps_poll()方法
3. 在这个方法中，阅读最新的TPV (时间位置速度)报告并返回lat long。
4. 返回到等待用户调用gps_poll()

Answer 1

您需要做的是定期轮询'session.next()‘-这里的问题是您处理的是一个串行接口-您得到的结果的顺序是被接收。由您来维护具有最新检索值的“current_value”。

如果您不轮询会话对象，最终您的UART FIFO将被填满，而且您也不会得到任何新的值。

考虑使用线程，不要等待用户调用gps_poll()，您应该进行轮询，当用户需要一个新的值时，他们使用'get_current_value()‘返回current_value。

从我的头顶上可以是这样简单的东西：

import threading
import time
from gps import *

class GpsPoller(threading.Thread):

   def __init__(self):
       threading.Thread.__init__(self)
       self.session = gps(mode=WATCH_ENABLE)
       self.current_value = None

   def get_current_value(self):
       return self.current_value

   def run(self):
       try:
            while True:
                self.current_value = self.session.next()
                time.sleep(0.2) # tune this, you might not get values that quickly
       except StopIteration:
            pass

if __name__ == '__main__':

   gpsp = GpsPoller()
   gpsp.start()
   # gpsp now polls every .2 seconds for new data, storing it in self.current_value
   while 1:
       # In the main thread, every 5 seconds print the current value
       time.sleep(5)
       print gpsp.get_current_value() 

Answer 2

对于任何使用现代版本的gpsd并且只在特定时间需要数据而不是流的人来说，上面的答案都是非常低效率和过于复杂的。

大多数GPSes每秒至少发送一次位置信息。据推测，由于许多基于gps的应用程序都需要实时更新，我看到的绝大多数gpsd客户端示例都使用了上述方法，从gpsd观察流并接收实时更新(大致与gps发送的频率相同)。

但是，如果(与OP的情况一样)您不需要流信息，而是在请求时只需要最后报告的位置(例如，通过用户交互或其他事件)，那么有一个更有效和更简单的方法:让gpsd缓存最新的位置信息，并在需要时进行查询。

gpsd JSON协议有一个?POLL;请求，它返回gpsd所看到的最新GPS信息。不必迭代gps消息的积压，并继续读取新消息以避免完全缓冲区，您可以在gpsd会话开始时发送?WATCH={"enable":true}消息，然后在需要时使用?POLL;查询最新的位置信息。响应是一个JSON对象，包含gpsd从GPS中看到的最新信息。

如果您正在使用Python3，我发现的最简单的方法是使用pypi上可用的gpsd-py3包。若要连接到gpsd，请获取最新的位置信息，并打印当前位置：

import gpsd
gpsd.connect()
packet = gpsd.get_current()
print(packet.position())

您可以在需要新的位置信息时重复gpsd.get_current()调用，并且在幕后，gpsd包将执行对gpsd的?POLL;调用，并返回一个表示响应的对象。

使用内置的gps模块进行此操作并不是非常简单，但是还有许多其他的Python客户端可用，而且与任何可以执行套接字通信的操作(包括使用telnet的示例)都有很小的关系。

$ telnet localhost 2947
Trying ::1...
Connected to localhost.
Escape character is '^]'.
{"class":"VERSION","release":"3.16","rev":"3.16","proto_major":3,"proto_minor":11}
?WATCH={"enable":true}
{"class":"DEVICES","devices":[{"class":"DEVICE","path":"/dev/pts/10","driver":"SiRF","activated":"2018-03-02T21:14:52.687Z","flags":1,"native":1,"bps":4800,"parity":"N","stopbits":1,"cycle":1.00}]}
{"class":"WATCH","enable":true,"json":false,"nmea":false,"raw":0,"scaled":false,"timing":false,"split24":false,"pps":false}
?POLL;
{"class":"POLL","time":"2018-03-02T21:14:54.873Z","active":1,"tpv":[{"class":"TPV","device":"/dev/pts/10","mode":3,"time":"2005-06-09T14:34:53.280Z","ept":0.005,"lat":46.498332203,"lon":7.567403907,"alt":1343.165,"epx":24.829,"epy":25.326,"epv":78.615,"track":10.3788,"speed":0.091,"climb":-0.085,"eps":50.65,"epc":157.23}],"gst":[{"class":"GST","device":"/dev/pts/10","time":"1970-01-01T00:00:00.000Z","rms":0.000,"major":0.000,"minor":0.000,"orient":0.000,"lat":0.000,"lon":0.000,"alt":0.000}],"sky":[{"class":"SKY","device":"/dev/pts/10","time":"2005-06-09T14:34:53.280Z","xdop":1.66,"ydop":1.69,"vdop":3.42,"tdop":3.05,"hdop":2.40,"gdop":5.15,"pdop":4.16,"satellites":[{"PRN":23,"el":6,"az":84,"ss":0,"used":false},{"PRN":28,"el":7,"az":160,"ss":0,"used":false},{"PRN":8,"el":66,"az":189,"ss":45,"used":true},{"PRN":29,"el":13,"az":273,"ss":0,"used":false},{"PRN":10,"el":51,"az":304,"ss":29,"used":true},{"PRN":4,"el":15,"az":199,"ss":36,"used":true},{"PRN":2,"el":34,"az":241,"ss":41,"used":true},{"PRN":27,"el":71,"az":76,"ss":42,"used":true}]}]}
?POLL;
{"class":"POLL","time":"2018-03-02T21:14:58.856Z","active":1,"tpv":[{"class":"TPV","device":"/dev/pts/10","mode":3,"time":"2005-06-09T14:34:53.280Z","ept":0.005,"lat":46.498332203,"lon":7.567403907,"alt":1343.165,"epx":24.829,"epy":25.326,"epv":78.615,"track":10.3788,"speed":0.091,"climb":-0.085,"eps":50.65,"epc":157.23}],"gst":[{"class":"GST","device":"/dev/pts/10","time":"1970-01-01T00:00:00.000Z","rms":0.000,"major":0.000,"minor":0.000,"orient":0.000,"lat":0.000,"lon":0.000,"alt":0.000}],"sky":[{"class":"SKY","device":"/dev/pts/10","time":"2005-06-09T14:34:53.280Z","xdop":1.66,"ydop":1.69,"vdop":3.42,"tdop":3.05,"hdop":2.40,"gdop":5.15,"pdop":4.16,"satellites":[{"PRN":23,"el":6,"az":84,"ss":0,"used":false},{"PRN":28,"el":7,"az":160,"ss":0,"used":false},{"PRN":8,"el":66,"az":189,"ss":45,"used":true},{"PRN":29,"el":13,"az":273,"ss":0,"used":false},{"PRN":10,"el":51,"az":304,"ss":29,"used":true},{"PRN":4,"el":15,"az":199,"ss":36,"used":true},{"PRN":2,"el":34,"az":241,"ss":41,"used":true},{"PRN":27,"el":71,"az":76,"ss":42,"used":true}]}]}

Answer 3

加上我的两分钱。

无论出于什么原因，我的覆盆子pi将继续执行线程，我将不得不硬重置pi。

所以我把sysnthesizerpatel和我在Dan的博客这里上找到的答案结合起来。

我的gps_poller类如下所示：

import os 
from gps import *
from time import *
import time 
import threading 

class GpsPoller(threading.Thread):

    def __init__(self):
        threading.Thread.__init__(self)
        self.session = gps(mode=WATCH_ENABLE)
        self.current_value = None 
        self.running = True 

    def get_current_value(self):
        return self.current_value

    def run(self):
        try:
            while self.running:
                self.current_value = self.session.next() 
        except StopIteration:
            pass

使用中的代码如下：

from gps_poll import *

if __name__ == '__main__':
    gpsp = GpsPoller()
    try: 
        gpsp.start() 
        while True:
            os.system('clear')
            report = gpsp.get_current_value()
            # print report 
            try: 
                if report.keys()[0] == 'epx':
                    print report['lat']
                    print report['lon']           
                time.sleep(.5)
            except(AttributeError, KeyError):
                pass 
            time.sleep(0.5)

    except(KeyboardInterrupt, SystemExit):
        print "\nKilling Thread.."
        gpsp.running = False 
        gpsp.join()

    print "Done.\nExiting." 

您还可以在这里找到代码：这里和这里