micropyGPS/micropyGPS.py

# MicropyGPS - a GPS NMEA sentence parser for Micropython/Python 3.X

#
# The MIT License (MIT)

# Copyright (c) 2014 Michael Calvin McCoy (calvin.mccoy@gmail.com)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
# documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit
# persons to whom the Software is furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
# Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
# OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


# TODO:
# Time Since First Fix
# Time Since Last Good Fix
# Statistics
# Sentence size bound checking

class MicropyGPS(object):
    """GPS NMEA Sentence Parser. Creates object that stores all relevant GPS data and statistics.
    Parses sentences one character at a time using update(). """

    # Max Number of Characters a valid sentence can be (based on GGA sentence)
    SENTENCE_LIMIT = 76

    def __init__(self, local_offset=0):
        """Setup GPS Object Status Flags, Internal Data Registers, etc"""

        #####################
        # Object Status Flags
        self.sentence_active = False
        self.active_segment = 0
        self.process_crc = False
        self.gps_segments = []
        self.crc_xor = 0
        self.char_count = 0

        #####################
        # Data From Sentences
        # Time
        self.timestamp = (0, 0, 0)
        self.date = (0, 0, 0)
        self.local_offset = local_offset

        # Position/Motion
        self.latitude = (0, 0.0, 'N')
        self.longitude = (0, 0.0, 'W')
        self.speed = (0.0, 0.0, 0.0)
        self.course = 0.0
        self.altitude = 0.0
        self.geoid_height = 0.0

        # GPS Info
        self.satellites_in_view = 0
        self.satellites_in_use = 0
        self.satellites_used = []
        self.last_sv_sentence = 0
        self.total_sv_sentences = 0
        self.satellite_data = dict()
        self.hdop = 0.0
        self.pdop = 0.0
        self.vdop = 0.0
        self.valid = False
        self.fix_stat = 0
        self.fix_type = 1

        # Object Constants
        self.__hemispheres = ('N', 'S', 'E', 'W')

    def gprmc(self):
        """Parse Recommended Minimum Specific GPS/Transit data (RMC)Sentence. Updates UTC timestamp, latitude,
        longitude, Course, Speed, and Date"""

        # UTC Timestamp
        try:
            utc_string = self.gps_segments[1]
            # Skip timestamp if receiver doesn't have one yet
            if utc_string:
                hours = int(utc_string[0:2]) + self.local_offset
                minutes = int(utc_string[2:4])
                seconds = float(utc_string[4:])
                self.timestamp = (hours, minutes, seconds)
        except ValueError:
            return False

        # Check Receiver Data Valid Flag
        if self.gps_segments[2] == 'A':  # Data from Receiver is valid

            # Longitude / Latitude
            try:
                # Latitude
                l_string = self.gps_segments[3]
                lat_degs = int(l_string[0:2])
                lat_mins = float(l_string[2:])
                lat_hemi = self.gps_segments[4]

                # Longitude
                l_string = self.gps_segments[5]
                lon_degs = int(l_string[0:3])
                lon_mins = float(l_string[3:])
                lon_hemi = self.gps_segments[6]
            except ValueError:
                return False

            if lat_hemi not in self.__hemispheres:
                return False

            if lon_hemi not in self.__hemispheres:
                return False

            # Speed
            try:
                spd_knt = float(self.gps_segments[7])
            except ValueError:
                return False

            # Date
            try:
                # NOTE!!! Date string is assumed to be year >=2000,
                # Sentences recorded in 90s will display as 209X!!!
                # FIXME if you want to parse old GPS logs or are time traveler
                date_string = self.gps_segments[9]
                day = date_string[0:2]
                month = date_string[2:4]
                year = date_string[4:6]
            except ValueError:
                return False

            # Course
            try:
                course = self.gps_segments[8]
            except ValueError:
                return False

            # TODO - Add Magnetic Variation

            # Update Object Data
            self.latitude = (lat_degs, lat_mins, lat_hemi)
            self.longitude = (lon_degs, lon_mins, lon_hemi)
            # Include mph and hm/h
            self.speed = (spd_knt, spd_knt * 1.151, spd_knt * 1.852)
            self.date = (day, month, year)
            self.course = course
            self.valid = True

        else:
            return False

        return True

    def gpvtg(self):
        """Parse Track Made Good and Ground Speed (VTG) Sentence. Updates speed and course"""
        try:
            course = self.gps_segments[1]
            spd_knt = float(self.gps_segments[5])
        except ValueError:
            return False

        # Include mph and hm/h
        self.speed = (spd_knt, spd_knt * 1.151, spd_knt * 1.852)
        self.course = course
        return True

    def gpgga(self):
        """Parse Global Positioning System Fix Data (GGA) Sentence. Updates UTC timestamp, latitude, longitude,
        fix status, satellites in use, Horizontal Dilution of Precision (HDOP), altitude, and geoid height"""

        try:
            # UTC Timestamp
            utc_string = self.gps_segments[1]

            # Skip timestamp if receiver doesn't have on yet
            if utc_string:
                hours = int(utc_string[0:2]) + self.local_offset
                minutes = int(utc_string[2:4])
                seconds = float(utc_string[4:])
            else:
                hours = 0
                minutes = 0
                seconds = 0.0

            # Number of Satellites in Use
            satellites_in_use = int(self.gps_segments[7])

            # Horizontal Dilution of Precision
            hdop = float(self.gps_segments[8])

            # Get Fix Status
            fix_stat = int(self.gps_segments[6])

        except ValueError:
            return False

        # Process Location and Speed Data if Fix is GOOD
        if fix_stat:

            # Longitude / Latitude
            try:
                # Latitude
                l_string = self.gps_segments[2]
                lat_degs = int(l_string[0:2])
                lat_mins = float(l_string[2:])
                lat_hemi = self.gps_segments[3]

                # Longitude
                l_string = self.gps_segments[4]
                lon_degs = int(l_string[0:3])
                lon_mins = float(l_string[3:])
                lon_hemi = self.gps_segments[5]
            except ValueError:
                return False

            if lat_hemi not in self.__hemispheres:
                return False

            if lon_hemi not in self.__hemispheres:
                return False

            # Altitude / Height Above Geoid
            try:
                altitude = float(self.gps_segments[9])
                geoid_height = float(self.gps_segments[11])
            except ValueError:
                return False

            # Update Object Data
            self.latitude = (lat_degs, lat_mins, lat_hemi)
            self.longitude = (lon_degs, lon_mins, lon_hemi)
            self.altitude = altitude
            self.geoid_height = geoid_height

        # Update Object Data
        self.timestamp = (hours, minutes, seconds)
        self.satellites_in_use = satellites_in_use
        self.hdop = hdop
        self.fix_stat = fix_stat

        return True

    def gpgsa(self):
        """Parse GNSS DOP and Active Satellites (GSA) sentence. Updates GPS fix type, list of satellites used in
        fix calculation, Position Dilution of Precision (PDOP), Horizontal Dilution of Precision (HDOP), and Vertical
        Dilution of Precision"""

        # Fix Type (None,2D or 3D)
        try:
            fix_type = int(self.gps_segments[2])
        except ValueError:
            return False

        # Read All (up to 12) Available PRN Satellite Numbers
        sats_used = []
        for sats in range(12):
            sat_number_str = self.gps_segments[3 + sats]
            if sat_number_str:
                try:
                    sat_number = int(sat_number_str)
                    sats_used.append(sat_number)
                except ValueError:
                    return False
            else:
                break

        # PDOP,HDOP,VDOP
        try:
            pdop = float(self.gps_segments[15])
            hdop = float(self.gps_segments[16])
            vdop = float(self.gps_segments[17])
        except ValueError:
            return False

        # Update Object Data
        self.fix_type = fix_type
        self.satellites_used = sats_used
        self.hdop = hdop
        self.vdop = vdop
        self.pdop = pdop

        return True

    def gpgsv(self):
        """Parse Satellites in View (GSV) sentence. Updates number of SV Sentences,the number of the last SV sentence
        parsed"""
        try:
            number_of_sv_sentences = int(self.gps_segments[1])
            current_sv_sentence = int(self.gps_segments[2])
            satellites_in_view = int(self.gps_segments[3])
        except ValueError:
            return False

        # Create a blank dict to store all the satellite data from this sentence in:
        # satellite PRN is key, tuple containing telemetry is value
        satellite_dict = dict()

        # Try to recover data for up to 4 satellites in sentence
        for sats in range(4, 20, 4):

            # If a PRN is present, grab satellite data
            if self.gps_segments[sats]:
                try:
                    sat_id = int(self.gps_segments[sats])
                    elevation = int(self.gps_segments[sats+1])
                    azimuth = int(self.gps_segments[sats+2])
                except ValueError:
                    return False

                try:  # SNR can be null (no value) when not tracking
                    snr = int(self.gps_segments[sats+3])
                except ValueError:
                    snr = None

            # If no PRN is found, then the sentence has no more satellites to read
            else:
                break

            # Add Satellite Data to Sentence Dict
            satellite_dict[sat_id] = (elevation, azimuth, snr)

        # Update Object Data
        self.total_sv_sentences = number_of_sv_sentences
        self.last_sv_sentence = current_sv_sentence
        self.satellites_in_view = satellites_in_view

        # For a new set of sentences, we either clear out the existing sat data or
        # update it as additional SV sentences are parsed
        if current_sv_sentence == 1:
            self.satellite_data = satellite_dict
        else:
            self.satellite_data.update(satellite_dict)

        return True

    def new_sentence(self):
        """Adjust Object Flags in Preparation for a New Sentence"""
        self.gps_segments = ['']
        self.active_segment = 0
        self.crc_xor = 0
        self.sentence_active = True
        self.process_crc = True
        self.char_count = 0

    def update(self, new_char):
        """Process a new input char and updates GPS object if necessary based on special characters ('$', ',', '*')
        Function builds a list of received string that are validate by CRC prior to parsing by the  appropriate
        sentence function. Returns sentence type on successful parse, None otherwise"""

        valid_sentence = False

        # Validate new_char is a printable char
        ascii_char = ord(new_char)

        if 33 <= ascii_char <= 126:
            self.char_count += 1

            # Check if a new string is starting ($)
            if new_char == '$':
                self.new_sentence()
                return None

            elif self.sentence_active:

                # Check if sentence is ending (*)
                if new_char == '*':
                    self.process_crc = False
                    self.active_segment += 1
                    self.gps_segments.append('')
                    return None

                # Check if a section is ended (,), Create a new substring to feed
                # characters to
                elif new_char == ',':
                    self.active_segment += 1
                    self.gps_segments.append('')

                # Store All Other printable character and check CRC when ready
                else:
                    self.gps_segments[self.active_segment] += new_char

                    # When CRC input is disabled, sentence is nearly complete
                    if not self.process_crc:

                        if len(self.gps_segments[self.active_segment]) == 2:
                            try:
                                final_crc = int(self.gps_segments[self.active_segment], 16)
                                if self.crc_xor == final_crc:
                                    valid_sentence = True
                            except ValueError:
                                pass  # CRC Value was deformed and could not have been correct

                # Update CRC
                if self.process_crc:
                    self.crc_xor ^= ascii_char

                # If a Valid Sentence Was received and it's a supported sentence, then parse it!!
                if valid_sentence:

                    # Clear Active Processing Flag
                    self.sentence_active = False
                    if self.gps_segments[0] in self.supported_sentences:

                        # parse the Sentence Based on the message type, return True if parse is clean
                        if self.supported_sentences[self.gps_segments[0]](self):

                            # Let host know that the GPS object was updated by returning parsed sentence type
                            return self.gps_segments[0]

                # Check that the sentence buffer isn't filling up with Garage waiting for the sentence to complete
                if self.char_count > self.SENTENCE_LIMIT:
                    self.sentence_active = False

        # Tell Host no new sentence was parsed
        return None

    #########################################
    # User Helper Functions
    # These functions make working with the GPS object data easier
    #########################################

    def satellite_data_updated(self):
        """
        Checks if the all the GSV sentences in a group have been read, making satellite data complete
        :return: boolean
        """
        if self.total_sv_sentences > 0 and self.total_sv_sentences == self.last_sv_sentence:
            return True
        else:
            return False

    def satellites_visible(self):
        """
        Returns a list of of the satellite PRNs currently visible to the receiver
        :return: list
        """
        return list(self.satellite_data.keys())

    # All the currently supported NMEA sentences    
    supported_sentences = {'GPRMC': gprmc, 'GPGGA': gpgga, 'GPVTG': gpvtg, 'GPGSA': gpgsa, 'GPGSV': gpgsv}

if __name__ == "__main__":

    test_RMC = ['$GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62',
                '$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A',
                '$GPRMC,225446,A,4916.45,N,12311.12,W,000.5,054.7,191194,020.3,E*68',
                '$GPRMC,180041.896,A,3749.1851,N,08338.7891,W,001.9,154.9,240911,,,A*7A',
                '$GPRMC,180049.896,A,3749.1808,N,08338.7869,W,001.8,156.3,240911,,,A*70',
                '$GPRMC,092751.000,A,5321.6802,N,00630.3371,W,0.06,31.66,280511,,,A*45']

    test_VTG = ['$GPVTG,232.9,T,,M,002.3,N,004.3,K,A*01']
    test_GGA = ['$GPGGA,180050.896,3749.1802,N,08338.7865,W,1,07,1.1,397.4,M,-32.5,M,,0000*6C']
    test_GSA = ['$GPGSA,A,3,07,11,28,24,26,08,17,,,,,,2.0,1.1,1.7*37',
                '$GPGSA,A,3,07,02,26,27,09,04,15,,,,,,1.8,1.0,1.5*33']
    test_GSV = ['$GPGSV,3,1,12,28,72,355,39,01,52,063,33,17,51,272,44,08,46,184,38*74',
                '$GPGSV,3,2,12,24,42,058,33,11,34,053,33,07,20,171,40,20,15,116,*71',
                '$GPGSV,3,3,12,04,12,204,34,27,11,324,35,32,11,089,,26,10,264,40*7B',
                '$GPGSV,3,1,11,03,03,111,00,04,15,270,00,06,01,010,00,13,06,292,00*74',
                '$GPGSV,3,2,11,14,25,170,00,16,57,208,39,18,67,296,40,19,40,246,00*74',
                '$GPGSV,3,3,11,22,42,067,42,24,14,311,43,27,05,244,00,,,,*4D']

    my_gps = MicropyGPS()
    sentence = ''
    for RMC_sentence in test_RMC:
        for y in RMC_sentence:
            sentence = my_gps.update(y)
        print('Parsed a', sentence, 'Sentence')
        print('Parsed Strings:', my_gps.gps_segments)
        print('Sentence CRC Value:', hex(my_gps.crc_xor))
        print('Longitude:', my_gps.longitude)
        print('Latitude', my_gps.latitude)
        print('UTC Timestamp:', my_gps.timestamp)
        print('Speed:', my_gps.speed)
        print('Date Stamp:', my_gps.date)
        print('Course', my_gps.course)
        print('Data is Valid', my_gps.valid)
        print('')

    for VTG_sentence in test_VTG:
        for y in VTG_sentence:
            sentence = my_gps.update(y)
        print('Parsed a', sentence, 'Sentence')
        print('Parsed Strings', my_gps.gps_segments)
        print('Sentence CRC Value:', hex(my_gps.crc_xor))
        print('Speed:', my_gps.speed)
        print('Course', my_gps.course)
        print('')

    for GGA_sentence in test_GGA:
        for y in GGA_sentence:
            sentence = my_gps.update(y)
        print('Parsed a', sentence, 'Sentence')
        print('Parsed Strings', my_gps.gps_segments)
        print('Sentence CRC Value:', hex(my_gps.crc_xor))
        print('Longitude', my_gps.longitude)
        print('Latitude', my_gps.latitude)
        print('UTC Timestamp:', my_gps.timestamp)
        print('Fix Status:', my_gps.fix_stat)
        print('Altitude:', my_gps.altitude)
        print('Height Above Geoid:', my_gps.geoid_height)
        print('Horizontal Dilution of Precision:', my_gps.hdop)
        print('Satellites in Use by Receiver:', my_gps.satellites_in_use)
        print('')

    for GSA_sentence in test_GSA:
        for y in GSA_sentence:
            sentence = my_gps.update(y)
        print('Parsed a', sentence, 'Sentence')
        print('Parsed Strings', my_gps.gps_segments)
        print('Sentence CRC Value:', hex(my_gps.crc_xor))
        print('Satellites Used', my_gps.satellites_used)
        print('Fix Type Code:', my_gps.fix_type)
        print('Horizontal Dilution of Precision:', my_gps.hdop)
        print('Vertical Dilution of Precision:', my_gps.vdop)
        print('Position Dilution of Precision:', my_gps.pdop)
        print('')

    for GSV_sentence in test_GSV:
        for y in GSV_sentence:
            sentence = my_gps.update(y)
        print('Parsed a', sentence, 'Sentence')
        print('Parsed Strings', my_gps.gps_segments)
        print('Sentence CRC Value:', hex(my_gps.crc_xor))
        print('SV Sentences Parsed', my_gps.last_sv_sentence)
        print('SV Sentences in Total', my_gps.total_sv_sentences)
        print('# of Satellites in View:', my_gps.satellites_in_view)
        data_valid = my_gps.satellite_data_updated()
        print('Is Satellite Data Valid?:', data_valid)
        if data_valid:
            print('Satellite Data:', my_gps.satellite_data)
            print('Satellites Visible:', my_gps.satellites_visible())
        print('')