NMEA GPRMC Python Parser

gprmc.py

#!/usr/bin/env python3

import sys
import time
import serial
import threading


class GPSRMC(object):
    def __init__(self, dev='/dev/ttyUSB0', timeout=0.5, interval=0.1):
        self.dev = dev
        self.timeout = timeout
        self.interval = interval
        self.ser = None

        self.nmea_sentence = ""
        self.utc = 0.0
        self.pos_status = ""
        self.lat = 0.0
        self.lat_dir = ""
        self.lon = 0.0
        self.lon_dir = ""
        self.speed_Kn = 0.0
        self.track_true = 0.0
        self.date = 0
        self.mag_var = 0.0
        self.var_dir = ""
        self.mode_ind = ""
        self.chksum = 0
        self.cnt = 0

        self.lock = threading.Lock()
        self.callback()

    def callback(self):
        try:
            if self.ser is None:
                print("Trying to open gps serial port:{}".format(self.dev))
                self.ser = serial.Serial(self.dev, timeout=self.timeout)
                print("GPS port opened")
        except OSError:
            print ('*** GPS ERROR: OS error (possibly serial port is not available)')
            time.sleep(3)
        except serial.SerialException:
            print ('*** GPS ERROR: serial port error (possibly device is reset, powered down or in sleep mode). Restarting reading process...')
            self.ser = None
            time.sleep(3)
            self.cnt += 1


        self.thr = threading.Timer(self.interval, self.callback)
        if self.cnt > 3:
            print("*** GPS not found")
            self.thr.cancel()
            # sys.exit()
            return False
        self.thr.start()
        with self.lock:
            header = "$GPRMC,"
            # received_data = "$GPRMC,144326.00,A,5107.0017737,N,11402.3291611,W,0.080,323.3,210307,0.0,E,A*20"  # test
            try:
                received_data = str(self.ser.readline())
            except serial.SerialException:
                self.ser.close()
                self.ser = None
                self.callback()
            if received_data.split(",")[0] == "b'$GPRMC":
                self.nmea_sentence = received_data.split(header, 1)[1].split(",")
                # print("GPRMC received", received_data)
                if not self.nmea_sentence[0]:
                    # print("NMEA:{}".format(self.nmea_sentence))
                    pass
                self.parse()

    def parse(self):
        nmea = self.nmea_sentence

        self.utc = nmea[0]
        self.pos_status = nmea[1]
        self.lat = self._convert_to_decimal_deg(nmea[2])
        self.lat_dir = nmea[3]
        if self.lat_dir == "S":
            self.lat = -self.lat
        self.lon = self._convert_to_decimal_deg(nmea[4])
        self.lon_dir = nmea[5]
        if self.lon_dir == "W":
            self.lon = -self.lon
        self.speed_Kn = 0.0 if nmea[6] == "" else float(nmea[6])
        self.track_true = nmea[7]
        self.date = nmea[8]
        self.mag_var = nmea[9]
        self.var_dir = nmea[10]
        self.mode_ind = nmea[11].split("*")[0]
        self.chksum = '*' + nmea[11].split("*")[1]

    @staticmethod
    def _convert_to_decimal_deg(dms_value):
        if dms_value == "":
            return -1.0
        decimal_value = float(dms_value) / 100.0
        degrees = int(decimal_value)
        mm_mmmm = (decimal_value - degrees) / 0.6
        dd = degrees + mm_mmmm

        return dd

    def close(self):
        self.thr.cancel()
        # self.ser.close()
    
    def __del__(self):
        print("closed")
        self.close()