GPS module data reading in Raspberry Pi - Mini Project: Build & Apply

GPS Module Data Reading

📖 Scenario: You have a Raspberry Pi connected to a GPS module. The GPS module sends location data as NMEA sentences over a serial connection. You want to read this data and extract the latitude and longitude.

🎯 Goal: Build a simple Python program that reads raw GPS data from the serial port, filters for GPGGA sentences, and extracts the latitude and longitude values.

📋 What You'll Learn

Create a serial connection to the GPS module

Read lines of data from the serial port

Identify GPGGA sentences in the data

Extract latitude and longitude from the GPGGA sentence

Print the extracted latitude and longitude

💡 Why This Matters

🌍 Real World

GPS modules are used in navigation, tracking, and location-based services. Reading GPS data on Raspberry Pi helps build projects like vehicle trackers, weather balloons, or outdoor robots.

💼 Career

Understanding serial communication and parsing GPS data is useful for embedded systems engineers, IoT developers, and robotics programmers.

1

Set up serial connection to GPS module

Import the serial module and create a serial connection called gps_serial with port "/dev/ttyS0" and baud rate 9600.

Raspberry Pi

# Import serial and create gps_serial connection
# Your code here

Hint

Use serial.Serial(port, baudrate) to create the connection.

2

Read a line of data from the GPS module

Use gps_serial.readline() to read one line of data from the GPS module and decode it to a string called line.

Raspberry Pi

import serial

gps_serial = serial.Serial("/dev/ttyS0", 9600)

# Read one line from gps_serial and decode it
# Your code here

Hint

Use decode('ascii', errors='replace') to convert bytes to string safely.

3

Check for GPGGA sentence and extract latitude and longitude

Check if line starts with "$GPGGA". If yes, split line by commas into parts. Extract latitude from parts[2] and longitude from parts[4].

Raspberry Pi

import serial

gps_serial = serial.Serial("/dev/ttyS0", 9600)

line = gps_serial.readline().decode('ascii', errors='replace').strip()

# Check if line starts with "$GPGGA" and extract latitude and longitude
# Your code here

Hint

Use startswith to check the sentence type and split(",") to separate fields.

4

Print the extracted latitude and longitude

Print the latitude and longitude variables using print(f"Latitude: {latitude}, Longitude: {longitude}").

Raspberry Pi

import serial

gps_serial = serial.Serial("/dev/ttyS0", 9600)

line = gps_serial.readline().decode('ascii', errors='replace').strip()

if line.startswith("$GPGGA"):
    parts = line.split(",")
    latitude = parts[2]
    longitude = parts[4]

# Print latitude and longitude
# Your code here

Hint

Use an f-string to format the output nicely.

Practice

1. What type of data does a GPS module typically send to a Raspberry Pi over a serial connection?

easy

A. Audio signals for navigation

B. Raw binary satellite signals

C. NMEA sentences containing location and time information

D. Image data from satellite cameras

Solution

1. Step 1: Understand GPS data format

   GPS modules send data in text format called NMEA sentences, which include location, time, and other info.

2. Step 2: Identify data type sent over serial

   The Raspberry Pi receives these NMEA sentences as strings over the serial port.

3. Final Answer:

   NMEA sentences containing location and time information -> Option C

4. Quick Check:

   GPS data = NMEA sentences [OK]

Hint: Remember GPS uses NMEA text sentences for data [OK]

Common Mistakes:

• Thinking GPS sends raw binary signals directly
• Confusing GPS data with audio or images
• Assuming GPS sends only coordinates without time

2. Which Python library is commonly used on Raspberry Pi to read serial data from a GPS module?

easy

A. socket

B. serial

C. os

D. math

Solution

1. Step 1: Identify library for serial communication

   The 'serial' library (pyserial) is used to read data from serial ports on Raspberry Pi.

2. Step 2: Confirm other libraries' purposes

   'socket' is for network, 'os' for system operations, 'math' for calculations, so they don't handle serial data.

3. Final Answer:

   serial -> Option B

4. Quick Check:

   Serial data reading = serial library [OK]

Hint: Use 'serial' library for serial port reading [OK]

Common Mistakes:

• Using 'socket' which is for network communication
• Confusing 'os' or 'math' as serial libraries
• Not installing pyserial before use

3. Given the Python code snippet reading GPS data, what will be printed if the GPS sends the sentence '$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47'?

import serial
ser = serial.Serial('/dev/ttyS0', 9600)
line = ser.readline().decode('ascii', errors='replace')
if line.startswith('$GPGGA'):
    print('GPS fix data:', line.strip())
else:
    print('Other data')

medium

A. GPS fix data: $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47

B. Other data

C. SyntaxError

D. No output

Solution

1. Step 1: Check if line starts with '$GPGGA'

   The line from GPS starts exactly with '$GPGGA', so the condition is True.

2. Step 2: Print the GPS fix data line

   Since condition is True, it prints 'GPS fix data:' followed by the full line without trailing newline.

3. Final Answer:

   GPS fix data: $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47 -> Option A

4. Quick Check:

   Line startswith $GPGGA = print GPS fix [OK]

Hint: Check string start with $GPGGA to print GPS fix [OK]

Common Mistakes:

• Ignoring the startswith condition
• Expecting syntax errors from decode
• Not stripping newline before print

4. Identify the error in this Python code snippet intended to read GPS data from serial port and fix it:

import serial
ser = serial.Serial('/dev/ttyS0', 9600)
line = ser.readline().decode('utf-8')
if line.startswith('$GPRMC'):
print('RMC data:', line)

medium

A. Indent the print statement inside the if block

B. Change decode to 'ascii' instead of 'utf-8'

C. Use ser.read() instead of ser.readline()

D. Remove the if condition

Solution

1. Step 1: Check Python indentation rules

   The print statement must be indented inside the if block to run conditionally.

2. Step 2: Confirm other parts are correct

   Using 'utf-8' decode and readline() is valid; removing if or changing decode is unnecessary.

3. Final Answer:

   Indent the print statement inside the if block -> Option A

4. Quick Check:

   Indentation error fixed by indenting print [OK]

Hint: Indent code inside if blocks properly [OK]

Common Mistakes:

• Ignoring indentation causing syntax error
• Changing decode unnecessarily
• Removing important condition

5. You want to extract latitude and longitude from the $GPRMC sentence received from a GPS module on Raspberry Pi. Which Python code snippet correctly parses and prints latitude and longitude from this sentence? Example sentence: $GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A

hard

A. lat = parts[1]
lon = parts[2]
print(f'Lat: {lat}, Lon: {lon}')

B. lat = line[3:10]
lon = line[11:20]
print('Latitude:', lat, 'Longitude:', lon)

C. lat = line.split()[2]
lon = line.split()[3]
print(lat, lon)

D. parts = line.split(',')
lat = parts[3] + ' ' + parts[4]
lon = parts[5] + ' ' + parts[6]
print(f'Latitude: {lat}, Longitude: {lon}')

Solution

1. Step 1: Split the NMEA sentence by commas

   Splitting by ',' gives a list where latitude is at index 3 and 4 (value and N/S), longitude at 5 and 6 (value and E/W).

2. Step 2: Combine latitude and direction, longitude and direction

   Concatenate parts[3] with parts[4] and parts[5] with parts[6] to get full coordinates.

3. Final Answer:

   parts = line.split(',') lat = parts[3] + ' ' + parts[4] lon = parts[5] + ' ' + parts[6] print(f'Latitude: {lat}, Longitude: {lon}') -> Option D

4. Quick Check:

   Split by comma, lat=3+4, lon=5+6 [OK]

Hint: Split sentence by commas, lat=3+4, lon=5+6 [OK]

Common Mistakes:

• Using wrong indexes for latitude and longitude
• Trying to slice string instead of splitting
• Ignoring direction letters N/S and E/W