main.py

"""
Read data from GPS sensor

CSV format:
timestamp, latitude, longitude, altitude
"""

import time
import utils
import smbus2


# Define the I2C bus and address for the SAM-M8Q module
I2C_BUS = utils.get_bus("gps")
GPS_ADDRESS = 0x42

# Initialize logger
logger = utils.init_logger("gps")

# Create an I2C bus instance
bus = smbus2.SMBus(I2C_BUS)


def convert_to_degrees(raw_value):
    """Convert NMEA raw latitude/longitude format to decimal degrees."""

    degrees = int(raw_value[:2])
    minutes = float(raw_value[2:])
    return degrees + minutes / 60


def read_gps_data():

    try:
        # Read 32 bytes of data from the GPS module
        data = bus.read_i2c_block_data(GPS_ADDRESS, 0xFF, 32)  # 0xFF is the register address to read data
        
        # Filter out initialization bytes (255)
        filtered_data = [byte for byte in data if byte != 255]
        
        return filtered_data
    except Exception as e:
        logger.warning(f"Error reading GPS data: {e}")
        return None


def parse_nmea_sentence(data):

    try:
        # Convert data to ASCII characters
        nmea_sentence = ''.join(chr(byte) for byte in data)
        return nmea_sentence
    except Exception as e:
        logger.warning(f"Error parsing NMEA sentence: {e}")
        return None


def extract_lat_lon_alt(nmea_sentence):

    latitude = None
    longitude = None
    altitude = None

    try:
        if nmea_sentence.startswith("$GNRMC") or nmea_sentence.startswith("$GPRMC"):
            parts = nmea_sentence.split(',')
            if len(parts) > 6 and parts[3] and parts[5]:
                # Extract latitude and longitude
                latitude = convert_to_degrees(parts[3])
                if parts[4] == 'S':
                    latitude = -latitude

                longitude = convert_to_degrees(parts[5])
                if parts[6] == 'W':
                    longitude = -longitude

        elif nmea_sentence.startswith("$GNGGA") or nmea_sentence.startswith("$GPGGA"):
            parts = nmea_sentence.split(',')
            if len(parts) > 9 and parts[2] and parts[4] and parts[9]:
                # Extract latitude and longitude
                latitude = convert_to_degrees(parts[2])
                if parts[3] == 'S':
                    latitude = -latitude

                longitude = convert_to_degrees(parts[4])
                if parts[5] == 'W':
                    longitude = -longitude

                # Extract altitude
                altitude = float(parts[9])

        # Adjusting longitude by a certain amount
        if longitude is not None:
            longitude -= 6.0  # Adjust longitude by -6.0 degrees
    except Exception as e:
        logger.warning(f"Error extracting latitude, longitude, and altitude: {e}")

    return latitude, longitude, altitude


def main():

    buffer = ""
    while True:

        # Sleep 80 ms to avoid high CPU usage
        time.sleep(0.08)

        # Read GPS data
        raw_data = read_gps_data()
        if not raw_data:
            continue

        # Append new data to buffer
        nmea_sentence_part = parse_nmea_sentence(raw_data)
        if not nmea_sentence_part:
            continue

        buffer += nmea_sentence_part

        # Split buffer into complete sentences
        sentences = buffer.split('\n')
        buffer = sentences[-1]  # Keep incomplete sentence in buffer

        for sentence in sentences[:-1]:
            # Extract and print latitude, longitude, and altitude
            lat, lon, alt = extract_lat_lon_alt(sentence)
            if lat is not None and lon is not None and alt is not None:
                logger.info(f"Latitude: {lat:.7f}, Longitude: {lon:.7f}, Altitude: {alt:.3f}m")
                utils.write_csv("gps", [lat, lon, alt])
                utils.send_data("gps", {"latitude": lat, "longitude": lon, "altitude": alt}, logger)


if __name__ == "__main__":

    main()