10

我一直在尝试使用python 2.6中的标准GPS (gps.py) 模块。这应该充当客户端并从在 Ubuntu 中运行的 gpsd 读取 GPS 数据。

根据 GPSD 网页上关于客户端设计的文档（GPSD Client Howto），我应该能够使用以下代码（对示例稍作修改）来获取最新的 GPS 读数（我主要感兴趣的是 lat long）

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() 它会给我来自队列底部的缓冲值（从会话开始时开始），而不是最新的 Gps 读数。有没有办法使用这个库获取更新的值？在某种程度上，寻求最新价值观的流？

有没有人有一个代码示例使用这个库来轮询 gps 并获得我正在寻找的值？

这是我正在尝试做的事情：

  1. 开始会话
  2. 等待用户在我的代码中调用 gps_poll() 方法
  3. 在此方法中读取最新的 TPV（时间位置速度）报告并返回 lat long
  4. 返回等待用户调用 gps_poll()
4

4 回答 4

20

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——你按照收到的顺序得到结果。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 将填满，并且您无论如何都不会获得任何新值。

考虑为此使用线程，不要等待用户调用 gps_poll()，您应该轮询，当用户想要一个新值时，他们使用返回 current_value 的 'get_current_value()'。

在我的脑海中，它可能就像这样简单：

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()
于 2011-05-26T23:49:09.463 回答
13

对于使用现代版本的 gpsd 并且仅在特定时间需要数据而不是流式传输的任何人，上述答案都非常低效且过于复杂。

大多数 GPS 每秒至少发送一次位置信息。据推测，由于许多基于 GPS 的应用程序需要实时更新，我见过的绝大多数 gpsd 客户端示例都使用上述方法从 gpsd 观看流并接收实时更新（或多或少与 gps 发送它们的频率一样） .

但是，如果（如在 OP 的情况下）您不需要流信息，而只需要在请求时（即通过用户交互或其他事件）时的最后报告位置，则有一种更有效和更简单的方法：让 gpsd缓存最新的位置信息，需要时查询。

gpsd JSON 协议有一个请求，它返回 gpsd 看到的?POLL;最新 GPS 信息。?WATCH={"enable":true}您可以在 gpsd 会话开始时发送一条消息，然后在需要时使用?POLL;. 响应是一个 JSON 对象，其中包含 gpsd 从 GPS 中看到的最新信息。

如果您使用的是 Python3，我发现最简单的方法是使用 pypi 上提供的gpsd-py3包。连接gpsd，获取最新位置信息，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，并且在后台 gpsd 包将执行对?POLL;gpsd 的调用并返回一个表示响应的对象。

使用内置gps模块执行此操作并不是非常简单，但是还有许多其他 Python 客户端可用，并且使用任何可以执行套接字通信的东西也相当简单，包括使用以下示例telnet：

$ 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}]}]}
于 2018-03-02T21:18:39.720 回答
2

加上我的两分钱。

无论出于何种原因，我的树莓派都会继续执行一个线程，我必须硬重置 pi。

所以我结合了 sysnthesizerpatel 和我在 Dan Mandel 的博客上找到的答案。

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."

您还可以在此处找到代码：Here和Here

于 2016-03-17T23:46:25.723 回答
0

我知道它是一个旧线程，但只是为了让每个人都能理解，您也可以pyembedded为此使用 python 库。

pip install pyembedded

from pyembedded.gps_module.gps import GPS
import time    

gps = GPS(port='COM3', baud_rate=9600)

while True:
    print(gps.get_lat_long())
    time.sleep(1)

https://pypi.org/project/pyembedded/

于 2020-12-27T12:11:29.373 回答