Python GPS模块：读取最新的GPS数据

Question

我一直在尝试使用标准GPS（gps.py）模块在python 2.6中。这应该是作为客户端，并从Ubuntu中运行的gpsd读取GPS数据。

根据客户端设计（GPSD Client Howto）上GPSD网页的文档，我应该能够使用下面的代码（稍微修改该例子）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 

如果我重复使用下一个（）它给了我缓冲值从队列的底部（从当会话开始），而不是最新的GPS读数。有没有办法使用这个库获得更新的值？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和获得我正在寻找的价值？

这里就是我想要做：

1. 启动会话
2. 等待用户调用gps_poll（）方法，在我的代码
3. 在此方法中阅读最新的TPV （时间位置速度）报告并返回拉特长
4. 回到等待用户调用gps_poll（）

Answer 1

你需要做的是定期轮询'session.next（）' - 这里的问题是你正在处理一个串行接口 - 你会按照收到的顺序得到结果。它取决于您维护具有最新检索值的“current_value”。

如果你不轮询会话对象，最终你的UART FIFO将被填满，你不会得到任何新的值。

考虑使用一个线程为此，不要等待用户调用gps_poll（），你应该轮询，当用户想要一个新值时，他们使用返回current_value的'get_current_value（）'。

关闭我的头顶，但也可能是如此简单：

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

添加我的两分钱。

无论出于何种原因，我的覆盆子pi会继续执行一个线程，我不得不重置pi。

所以我把sysnthesizerpatel和我在Dan Mandel的博客here上找到的答案结合起来。

我gps_poller类看起来是这样的：

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 

和所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." 

你也可以在这里找到代码：Here和Here

Answer 3

的以上回答使用的GPSD的现代版本，并需要在只有特定的时间的数据，而不是流是非常低效和任何人过于复杂。

大多数GPSes每秒传送位置信息至少一次。大概是因为许多基于GPS的应用程序的愿望实时更新，绝大多数的GPSD客户端的例子我见过的使用看，从通用产品安全指令流和接收实时更新的上述方法（或多或少尽可能多的GPS将它们发送） 。但是，如果（如在OP的情况下），你不需要需要流信息，但只要需要最后报告的位置（即通过用户交互或其他事件），就需要最后报告的位置，更简单的方法：让gpsd缓存最新的位置信息，并在需要时查询它。

gpsd JSON protocol有一个?POLL;请求，它返回gpsd已经看到的最新GPS信息。而不必遍历的GPS信息的积压，并不断地阅读新邮件，以避免全缓冲的，你可以在GPSD会话开始发送?WATCH={"enable":true}消息，然后查询最新的位置信息，只要你有?POLL;需要它。响应是包含gpsd从GPS中看到的最新信息的单个JSON对象。

如果您使用Python3，我发现最简单的方法是使用PyPI上可用的gpsd-py3包。要连接到GPSD，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()) 

可以重复，只要你想新的位置信息gpsd.get_current()呼叫，以及幕后的GPSD包将执行?POLL;调用gpsd并返回表示响应的对象。

与内置gps模块不是非常简单的这样做，但也有一些其他的Python客户可用，并且它也是相当琐碎与任何可以进行socket通信，包括使用telnet这个例子做：

$ 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}]}]}