adafruit_gps.py

# The MIT License (MIT)
#
# Copyright (c) 2017 Tony DiCola for Adafruit Industries
#
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# of this software and associated documentation files (the "Software"), to deal
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# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
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# 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
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# THE SOFTWARE.
"""
`adafruit_gps`
====================================================

GPS parsing module.  Can parse simple NMEA data sentences from serial GPS
modules to read latitude, longitude, and more.

* Author(s): Tony DiCola, Alexandre Marquet.

Implementation Notes
--------------------

**Hardware:**

* Adafruit `Ultimate GPS Breakout <https://www.adafruit.com/product/746>`_
* Adafruit `Ultimate GPS FeatherWing <https://www.adafruit.com/product/3133>`_

**Software and Dependencies:**

* MicroPython:
    https://github.com/micropython/micropython

"""
__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/alexmrqt/Adafruit_CircuitPython_GPS.git"

# Internal helper parsing functions.
# These handle input that might be none or null and return none instead of
# throwing errors.
def _parse_degrees(nmea_data):
    # Parse a NMEA lat/long data pair 'dddmm.mmmm' into a pure degrees value.
    # Where ddd is the degrees, mm.mmmm is the minutes.
    if nmea_data is None or len(nmea_data) < 3:
        return None
    raw = float(nmea_data.decode())
    deg = raw // 100
    minutes = raw % 100
    return deg + minutes/60

def _parse_int(nmea_data):
    if nmea_data is None or nmea_data == b'':
        return None
    return int(nmea_data)

def _parse_float(nmea_data):
    if nmea_data is None or nmea_data == b'':
        return None
    return float(nmea_data.decode())

# lint warning about too many attributes disabled
#pylint: disable-msg=R0902
class GPS:
    """GPS parsing module.  Can parse simple NMEA data sentences from serial GPS
    modules to read latitude, longitude, and more.

    :param uart: The `UART` object to use.
    """
    def __init__(self, uart):
        self._uart = uart
        # Initialize null starting values for GPS attributes.
        self.timestamp_utc = None
        self.latitude = None
        self.longitude = None
        self.fix_quality = None
        self.satellites = None
        self.horizontal_dilution = None
        self.altitude_m = None
        self.height_geoid = None
        self.velocity_knots = None
        self.speed_knots = None
        self.track_angle_deg = None

    def update(self):
        """Check for updated data from the GPS module and process it
        accordingly.  Returns True if new data was processed, and False if
        nothing new was received.
        """
        # Grab a sentence and check its data type to call the appropriate
        # parsing function.
        sentence = self._parse_sentence()
        if sentence is None:
            return False
        data_type, args = sentence
        data_type = data_type.upper()
        if data_type == b'GPGGA':      # GGA, 3d location fix
            self._parse_gpgga(args)
        elif data_type == b'GPRMC':    # RMC, minimum location info
            self._parse_gprmc(args)
        return True

    def send_command(self, command, add_checksum=True):
        """Send a command string to the GPS.  If add_checksum is True (the
        default) a NMEA checksum will automatically be computed and added.
        Note you should NOT add the leading $ and trailing * to the command
        as they will automatically be added!
        """
        self._uart.write('$')
        self._uart.write(command)
        if add_checksum:
            checksum = 0
            for char in command:
                checksum ^= ord(char)
            self._uart.write('*')
            self._uart.write('{:02x}'.format(checksum).upper())
        self._uart.write('\r\n')

    @property
    def has_fix(self):
        """True if a current fix for location information is available."""
        return self.fix_quality is not None and self.fix_quality >= 1

    def _parse_sentence(self):
        # Parse any NMEA sentence that is available.
        sentence = self._uart.readline()
        if sentence is None or sentence == b'' or len(sentence) < 1:
            return None
        sentence = sentence.strip()
        # Look for a checksum and validate it if present.
        if len(sentence) > 7 and sentence[-3] == ord('*'):
            # Get included checksum, then calculate it and compare.
            expected = int(sentence[-2:], 16)
            actual = 0
            for i in range(1, len(sentence)-3):
                actual ^= sentence[i]
            if actual != expected:
                return None  # Failed to validate checksum.
            # Remove checksum once validated.
            sentence = sentence[:-3]
        # Parse out the type of sentence (first string after $ up to comma)
        # and then grab the rest as data within the sentence.
        delineator = sentence.find(b',')
        if delineator == -1:
            return None  # Invalid sentence, no comma after data type.
        data_type = sentence[1:delineator]
        return (data_type, sentence[delineator+1:])

    def _parse_gpgga(self, args):
        # Parse the arguments (everything after data type) for NMEA GPGGA
        # 3D location fix sentence.
        data = args.split(b',')
        if data is None or len(data) != 14:
            return  # Unexpected number of params.
        # Parse fix time.
        time_utc = int(_parse_float(data[0]))
        if time_utc is not None:
            hours = time_utc // 10000
            mins = (time_utc // 100) % 100
            secs = time_utc % 100
            # Set or update time to a friendly python time struct.
            if self.timestamp_utc is not None:
                self.timestamp_utc = (
                    self.timestamp_utc[0], self.timestamp_utc[1],
                    self.timestamp_utc[2], hours, mins, secs, 0, 0)
            else:
                self.timestamp_utc = (0, 0, 0, hours, mins, secs, 0, 0)
        # Parse latitude and longitude.
        self.latitude = _parse_degrees(data[1])
        if self.latitude is not None and \
           data[2] is not None and data[2].lower() == b's':
            self.latitude *= -1.0
        self.longitude = _parse_degrees(data[3])
        if self.longitude is not None and \
           data[4] is not None and data[4].lower() == b'w':
            self.longitude *= -1.0
        # Parse out fix quality and other simple numeric values.
        self.fix_quality = _parse_int(data[5])
        self.satellites = _parse_int(data[6])
        self.horizontal_dilution = _parse_float(data[7])
        self.altitude_m = _parse_float(data[8])
        self.height_geoid = _parse_float(data[10])

    def _parse_gprmc(self, args):
        # Parse the arguments (everything after data type) for NMEA GPRMC
        # minimum location fix sentence.
        data = args.split(b',')
        if data is None or len(data) < 11 or data[0] is None:
            return  # Unexpected number of params.
        # Parse fix time.
        time_utc = int(_parse_float(data[0]))
        if time_utc is not None:
            hours = time_utc // 10000
            mins = (time_utc // 100) % 100
            secs = time_utc % 100
            # Set or update time to a friendly python time struct.
            if self.timestamp_utc is not None:
                self.timestamp_utc = (
                    self.timestamp_utc[0], self.timestamp_utc[1],
                    self.timestamp_utc[2], hours, mins, secs, 0, 0)
            else:
                self.timestamp_utc = (0, 0, 0, hours, mins, secs, 0, 0)
        # Parse status (active/fixed or void).
        status = data[1]
        self.fix_quality = 0
        if status is not None and status.lower() == b'a':
            self.fix_quality = 1
        # Parse latitude and longitude.
        self.latitude = _parse_degrees(data[2])
        if self.latitude is not None and \
           data[3] is not None and data[3].lower() == b's':
            self.latitude *= -1.0
        self.longitude = _parse_degrees(data[4])
        if self.longitude is not None and \
           data[5] is not None and data[5].lower() == b'w':
            self.longitude *= -1.0
        # Parse out speed and other simple numeric values.
        self.speed_knots = _parse_float(data[6])
        self.track_angle_deg = _parse_float(data[7])
        # Parse date.
        if data[8] is not None and len(data[8]) == 6:
            day = int(data[8][0:2])
            month = int(data[8][2:4])
            year = 2000 + int(data[8][4:6])  # Y2k bug, 2 digit date assumption.
                                             # This is a problem with the NMEA
                                             # spec and not this code.
            if self.timestamp_utc is not None:
                # Replace the timestamp with an updated one.
                self.timestamp_utc = (year, month, day,
                                                       self.timestamp_utc[3],
                                                       self.timestamp_utc[4],
                                                       self.timestamp_utc[5],
                                                       0,
                                                       0)
            else:
                # Time hasn't been set so create it.
                self.timestamp_utc = (year, month, day, 0, 0, 0, 0, 0)