How can I read GPS data under Linux?

Question

I used win7 before to read the GPS data from the com port. From now on I would like to read the data under Ubuntu but the same code is not working. Here is my code:

import serial, sys, time, threading
from datetime import datetime, timedelta    

class MeasureModule():
    def __init__(self, port, baudrate, sync_time=0, sync_nr=0):
        self.port = port;
        self.baudrate = baudrate;

    def start(self):
        try:
            self.serial = serial.serial_for_url(self.port, self.baudrate, timeout=1)
        except AttributeError:            
            self.serial = serial.Serial(self.port, self.baudrate, timeout=1)
        start = time.clock()
        while(time.clock()-start<11):     
            data  = self.readline()        
            print(data)

        self.stop();                    

    def stop(self):
        self.serial.close()   

    def readline(self, timeout=1, endline='\n'):
        buff='';
        try:            
            tic = time.clock()
            ch = self.character(self.serial.read(1))

            # you can use if not ('\n' in buff) too if you don't like re
            while ((time.clock() - tic) < timeout) and (not ch in endline):
                buff += ch                
                ch = self.character(self.serial.read(1))

        except serial.SerialException, e:
            return buff

        return buff

    def character(self,b):
        if sys.version_info >= (3, 0):
            return b.decode('latin1')
        else:
            return b

I called the function in the following way:

for i in range (0,4):
    try:    
        print "Starting measurement /dev/ttyACM%d" % i
        gs = GPSModule('/dev/ttyACM%d' % i, 4800, 1, 1)
        gs.start()
    except:
        print "Unable to connect"

run@FXR:/dev$ dmesg  | grep tty
[    0.000000] console [tty0] enabled
[    4.764464] cdc_acm 2-1.6:1.1: ttyACM0: USB ACM device
[    4.767620] cdc_acm 2-1.6:1.3: ttyACM1: USB ACM device
[    4.771525] cdc_acm 2-1.6:1.9: ttyACM2: USB ACM device
[    4.808622] usb 2-1.4.4: pl2303 converter now attached to ttyUSB0

But I'm not receiving anything.

How can I do the same things under Ubuntu? How can I read the GPS data from com port?

Answer 1

Heres some code I have tested and definitely works under Ubuntu 18.04 with a Globalsat BU-353N5 USB GPS device, using python 3.6

Run lsusb on linux to confirm it can see the GPS unit before you run the python code.

I ran this on my linux PC and put the USB receiver on the window ledge, and it seemed to work fine.

Note the ".decode()" added - this gets around a potential string error "type object 'str' has no attribute" that can occur sometimes.

My GPS output in Australia seems to output GNGGA, I have seen GPGGA output listed in the USA, you will need to adapt the code below what to what the gps unit spits out.

---

import serial

ser = serial.Serial('/dev/ttyUSB0',4800,timeout=5)

while 1:
    line = ser.readline().decode()
    splitline = line.split(',')

    if splitline[0] == '$GNGGA':
        latitude = line[18:29]
        longitude =line[30:42]
        print(line)
        print('latitude = ',latitude)
        print('longitude =',longitude)
        print('How to read : 3824.3139  means 38 deg 24.3139 mins')
       break

Answer 2

You probably have to add yourself to the group that the gps is under. This is posted really late, but I recently tried to configure a usb gps puck on linux, and I had to do sudo adduser -aG USERMAME dialout in the terminal. This just adds the user to the group (dialout) which the gps is under. If you don't know the group, cd to /dev (in terminal) and type ll (or ls -Flh if that doesn't work) This will diplay all of the permissions and groups. There is one column that is of particular interest; this is one of the last columns (I think third to last -- sorry, I'm on Windows right now), and you might see about six or seven items in the list called "dialout". If your file -- your usb -- shows up there, then that is the group. Otherwise, just look for the group and sudo adduser... yourself.

Be sure you log out first, and then -- after logging back in -- go to the terminal again and type cat /dev/ttyACM0. If you still see nothing, then you need to configure and tell it the correct rate at which to dump its info (the baud rate); so, type (as someone else mentioned) stty -F /dev/ttyACM0 4800 which configures the baud rate to 4800. You should google the correct baud rate, but the last command essentially says, take this file (-F) and speak to me at this rate (4800).

I hope this helps someone because I certainly had some trouble getting my usb gps puck to work on linux-mint. Good luck to all linux users (I'm a recent convert). :D

Answer 3

Ok!

This code is VEEERY Ugly and Old I did that in 2006 I was a beginner and naive.

Now baby steps!

1. Use the command dmesg or check your console messages to know WHICH USB device is attached your GPS. In MY CASE was USB0

2. After that play with this code

---

import serial
import socket

ser = serial.Serial('/dev/ttyUSB0', 4800, timeout=1)
latitude = ''
longitude = ''
def readgps(latitude,longitude):
    """Read the GPG LINE using the NMEA standard"""
    while True:
        line = ser.readline()
        if "GPGGA" in line:
            latitude = line[18:26] #Yes it is positional info for lattitude
            longitude = line[31:39] #do it again
            return(latitude,longitude)
    print "Finished"

---

Sure you have to call the function ;) please do not forget.

Remeber the gps is always sending data and communicating.

For educational purposes do a : print line after ser.readline()

so you can see the whole data not only lat and long coordinates.

Remeber the USB GPS is just a fancy serial device ;) This code is very simple and I am sure you will understand and make WAY better code/programs.

Answer 4

You don't open /dev/ttyUSB0 with your program. How is your GPS module plugged ?

What happens if you do :

stty -F /dev/ttyACM0 4800
cat /dev/ttyACM0

in a console ?