GPS module data reading in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of GPS NMEA sentence parsing

What is the output of this Python code that parses a GPS NMEA sentence to extract latitude and longitude?

Raspberry Pi

nmea_sentence = "$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47"

parts = nmea_sentence.split(",")
lat_raw = parts[2]
lat_dir = parts[3]
lon_raw = parts[4]
lon_dir = parts[5]

lat_deg = int(lat_raw[:2])
lat_min = float(lat_raw[2:])
lon_deg = int(lon_raw[:3])
lon_min = float(lon_raw[3:])

latitude = lat_deg + lat_min / 60
longitude = lon_deg + lon_min / 60

if lat_dir == "S":
    latitude = -latitude
if lon_dir == "W":
    longitude = -longitude

print(f"Latitude: {latitude:.6f}, Longitude: {longitude:.6f}")

A Latitude: 48.117300, Longitude: 11.516667

B Latitude: 48.703800, Longitude: 113.100000

C Latitude: 4.807038, Longitude: 11.310000

D Latitude: 48.117300, Longitude: -11.516667

💡 Hint

Remember that latitude degrees are first two digits, longitude degrees are first three digits.

The code extracts degrees and minutes from the NMEA sentence and converts minutes to decimal degrees. Latitude is 48 degrees and 7.038 minutes, which is 48 + 7.038/60 = 48.1173. Longitude is 11 degrees and 31.000 minutes, which is 11 + 31/60 = 11.516667. Directions N and E keep values positive.

🧠 Conceptual

intermediate

Understanding GPS data update frequency

A GPS module connected to a Raspberry Pi outputs NMEA sentences every second. What is the typical update frequency of GPS position data in Hertz (Hz)?

A 1 Hz

B 60 Hz

C 0.1 Hz

D 10 Hz

💡 Hint

One update per second means how many updates per second?

GPS modules commonly output data once per second, which equals 1 Hertz (1 update per second).

🔧 Debug

advanced

Identify the error in GPS serial reading code

What error will this Python code raise when reading GPS data from serial port on Raspberry Pi?

Raspberry Pi

import serial

ser = serial.Serial('/dev/ttyS0', 9600, timeout=1)
line = ser.readline()
print(line.decode('utf-8'))
ser.close()

A AttributeError

B serial.SerialException

C No error, prints GPS data line

D UnicodeDecodeError

💡 Hint

Is the serial port and baud rate correct? Is decoding done properly?

The code opens the serial port, reads a line, decodes bytes to string, and prints it. If the GPS module is connected and sending data, this works without error.

❓ Predict Output

advanced

Output of GPS coordinate conversion function

What is the output of this function converting NMEA latitude format to decimal degrees?

Raspberry Pi

def nmea_to_decimal(coord, direction):
    degrees = int(coord[:2])
    minutes = float(coord[2:])
    decimal = degrees + minutes / 60
    if direction in ['S', 'W']:
        decimal = -decimal
    return round(decimal, 6)

print(nmea_to_decimal('4807.038', 'N'))

A 4807.038

B 48.1173

C 4.807038

D Error: ValueError

💡 Hint

NMEA latitude format is DDMM.mmmm, so slice first 2 characters for degrees.

The function slices first 2 characters for degrees ('48') and the rest for minutes ('07.038'). Then computes 48 + 7.038/60 = 48.1173, rounds to 6 decimal places, and since direction is 'N', keeps positive. Python prints it as 48.1173.

🧠 Conceptual

expert

Choosing correct serial port for GPS on Raspberry Pi

Which serial port is typically used to connect a GPS module on a Raspberry Pi running Raspberry Pi OS with default settings?

A /dev/ttyAMA0

B /dev/ttyUSB0

C /dev/ttyS0

D /dev/serial0

💡 Hint

Raspberry Pi uses a symbolic link for the primary UART serial port.

On Raspberry Pi OS, /dev/serial0 is a symbolic link to the primary UART port, which can be /dev/ttyAMA0 or /dev/ttyS0 depending on model and configuration. This is the recommended port for GPS modules connected via UART.