Python GPS模块：读取最新的GPS D

Question

我一直在尝试使用python中的标准GPS（GPS.py）模块。这应该是一个客户端，从运行在Ubuntu中的gpsd读取GPS数据。

根据客户设计的GPSD网页（GPSD Client Howto）中的文档，我应该能够使用以下代码（从示例中稍作修改）获取最新的GPS读数（lat long是我主要感兴趣的内容）

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（），它将从队列底部（从会话启动时）提供缓冲值，而不是最新的Gps读数。是否有方法使用此库获取更新的值？在某种程度上，寻找最新的价值流？

有没有人有一个代码示例使用这个库来轮询gps并获取我正在寻找的值？

以下是我要做的：

1. 启动会话
2. 等待用户在我的代码中调用gps_poll（）方法
3. 在这个方法中，读取最新的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（）”—这里的问题是您正在处理一个串行接口—您将按接收结果的顺序获取结果。由您来维护具有最新检索值的“当前值”。

如果不轮询session对象，最终UART FIFO将填满，并且无论如何也不会得到任何新值。

考虑为此使用一个线程，不要等待用户调用gps_poll（），您应该正在轮询，当用户需要新值时，他们会使用返回当前值的“get_current_value（）”。

从我的头顶上看，可能是这样简单的事情：

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

加上我的两分钱。

不管出于什么原因，我的树莓pi将继续执行一个线程，我将不得不硬重置pi。

所以我把Synthesizerpatel和我在DanMandel博客上找到的答案结合起来。

我的gps轮询器类如下所示：

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

使用的代码如下所示：

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." 

您也可以在这里找到代码：Here和Here

Answer 3

上面的答案对于任何使用gpsd的现代版本并且只在特定时间需要数据的人来说都是非常低效和过于复杂的，而不是流媒体。

大多数gpse每秒至少发送一次位置信息。大概是因为许多基于GPS的应用程序都需要实时更新，所以我看到的绝大多数gpsd客户机示例都使用上述方法从gpsd观看流并接收实时更新（或多或少是GPS发送的）。

然而，如果（在OP的例子中）您不需要流式信息，而只需要在请求时（即通过用户交互或其他事件）最后报告的位置，则有一种更高效和更简单的方法：让gpsd缓存最新的位置信息，并在需要时进行查询。

gpsd JSON protocol有一个?POLL;请求，该请求返回gpsd看到的最新GPS信息。不必迭代gps消息的积压，并不断读取新消息以避免缓冲区已满，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;查询最新位置信息。响应是一个JSON对象，包含gpsd从GPS上看到的最新信息。

如果您使用的是Python3，那么我找到的最简单的方法就是使用pypi上提供的gpsd-py3包。要连接到gpsd，请获取最新的位置信息，然后打印当前位置：

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

您可以在需要新位置信息时重复gpsd.get_current()调用，在后台，gpsd包将执行对gpsd的?POLL;调用并返回表示响应的对象。

使用内置的gps模块来实现这一点并不是非常简单，但是有许多其他Python客户机可用，而且对于任何可以执行套接字通信的对象都是非常简单的，包括这个使用telnet的示例：

$ 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}]}]}