Here are three examples of how to use python to get GPS data from a GPS receiver attached to a Raspberry Pi.
- Using GPSD client libraries
- Manually parsing NMEA sentences
- Using pynmea2 to parse NMEA sentences
GPSD client libraries
The gpsd client libraries are based on JSON. The JSON objects have a “class” attribute (E.g. TPV, SKY, DEVICE.etc…) which can be used to filter on different information.
This guide shows how to get gpsd up an running on a Raspberry Pi.
The example python script below filters on the TPV class, which is the Time Position Velocity report and then prints out the relevant information.
#! /usr/bin/python
from gps import *
import time
gpsd = gps(mode=WATCH_ENABLE|WATCH_NEWSTYLE)
print 'latitude\tlongitude\ttime utc\t\t\taltitude\tepv\tept\tspeed\tclimb' # '\t' = TAB to try and output the data in columns.
try:
while True:
report = gpsd.next() #
if report['class'] == 'TPV':
print getattr(report,'lat',0.0),"\t",
print getattr(report,'lon',0.0),"\t",
print getattr(report,'time',''),"\t",
print getattr(report,'alt','nan'),"\t\t",
print getattr(report,'epv','nan'),"\t",
print getattr(report,'ept','nan'),"\t",
print getattr(report,'speed','nan'),"\t",
print getattr(report,'climb','nan'),"\t"
time.sleep(1)
except (KeyboardInterrupt, SystemExit): #when you press ctrl+c
print "Done.\nExiting."
This python script filters on the SKY class and prints out satellite information.
#! /usr/bin/python
from gps import *
import time
import os
gpsd = gps(mode=WATCH_ENABLE|WATCH_NEWSTYLE)
try:
while True:
report = gpsd.next() #
if report['class'] == 'SKY':
os.system('clear')
print ' Satellites (total of', len(gpsd.satellites) , ' in view)'
for i in gpsd.satellites:
print 't', i
print '\n\n'
print 'PRN = PRN ID of the satellite. 1-63 are GNSS satellites, 64-96 are GLONASS satellites, 100-164 are SBAS satellites'
print 'E = Elevation in degrees'
print 'As = Azimuth, degrees from true north'
print 'ss = Signal stength in dB'
print 'used = Used in current solution?'
time.sleep(1)
except (KeyboardInterrupt, SystemExit): #when you press ctrl+c
print "Done.\nExiting."
Manually parsing NMEA sentences
The python script below shows how to access GPS data by connecting directly to the serial interface.
It filters on $GPRMC NMEA sentences and then splits the well know attributes into different variables.
import serial
port = "/dev/serial0"
def parseGPS(data):
# print "raw:", data #prints raw data
if data[0:6] == "$GPRMC":
sdata = data.split(",")
if sdata[2] == 'V':
print "no satellite data available"
return
print "---Parsing GPRMC---",
time = sdata[1][0:2] + ":" + sdata[1][2:4] + ":" + sdata[1][4:6]
lat = decode(sdata[3]) #latitude
dirLat = sdata[4] #latitude direction N/S
lon = decode(sdata[5]) #longitute
dirLon = sdata[6] #longitude direction E/W
speed = sdata[7] #Speed in knots
trCourse = sdata[8] #True course
date = sdata[9][0:2] + "/" + sdata[9][2:4] + "/" + sdata[9][4:6]#date
print "time : %s, latitude : %s(%s), longitude : %s(%s), speed : %s, True Course : %s, Date : %s" % (time,lat,dirLat,lon,dirLon,speed,trCourse,date)
def decode(coord):
#Converts DDDMM.MMMMM > DD deg MM.MMMMM min
x = coord.split(".")
head = x[0]
tail = x[1]
deg = head[0:-2]
min = head[-2:]
return deg + " deg " + min + "." + tail + " min"
print "Receiving GPS data"
ser = serial.Serial(port, baudrate = 9600, timeout = 0.5)
while True:
data = ser.readline()
parseGPS(data)
Using pynmea2 to parse NMEA sentences
The python script below shows how to access GPS data by connecting directly to the serial interface.
It filters on $GPGGA NMEA sentences and then uses pynmea2 to parse the data.
Pynmea2 can be installed with;
pi@raspberrypi ~ $ pip install pynmea2
import serial
import pynmea2
port = "/dev/serial0"
def parseGPS(str):
if str.find('GGA') > 0:
msg = pynmea2.parse(str)
print "Timestamp: %s -- Lat: %s %s -- Lon: %s %s -- Altitude: %s %s -- Satellites: %s" % (msg.timestamp,msg.lat,msg.lat_dir,msg.lon,msg.lon_dir,msg.altitude,msg.altitude_units,msg.num_sats)
serialPort = serial.Serial(port, baudrate = 9600, timeout = 0.5)
while True:
str = serialPort.readline()
parseGPS(str)
