GPS module data reading in Raspberry Pi

Introduction

We read GPS module data to know the exact location and time. This helps in navigation and tracking.

When you want to find your current position on a map.

When building a device that tracks movement or routes.

When you need accurate time from satellites.

When creating a project that logs travel paths.

When you want to trigger actions based on location.

Syntax

Raspberry Pi

import serial
import time

# Open serial port to GPS module
ser = serial.Serial('/dev/serial0', 9600, timeout=1)

while True:
    line = ser.readline().decode('ascii', errors='replace')
    if line.startswith('$GPGGA'):
        print(line.strip())

Use the correct serial port for your GPS module (e.g., '/dev/serial0').

GPS data comes in NMEA sentences, starting with $ and a code like $GPGGA.

Examples

Read one line of raw GPS data and print it.

Raspberry Pi

import serial

ser = serial.Serial('/dev/serial0', 9600, timeout=1)
line = ser.readline().decode('ascii', errors='replace')
print(line)

Filter and print only the $GPRMC sentences which contain recommended minimum GPS data.

Raspberry Pi

import serial

ser = serial.Serial('/dev/serial0', 9600, timeout=1)

while True:
    line = ser.readline().decode('ascii', errors='replace')
    if line.startswith('$GPRMC'):
        print('RMC sentence:', line.strip())

Sample Program

This program reads GPS data continuously from the GPS module connected to the Raspberry Pi. It prints only the $GPGGA sentences, which include position and fix data. You can stop it anytime with Ctrl+C.

Raspberry Pi

import serial
import time

# Open serial port to GPS module
ser = serial.Serial('/dev/serial0', 9600, timeout=1)

print('Reading GPS data... Press Ctrl+C to stop.')

try:
    while True:
        line = ser.readline().decode('ascii', errors='replace')
        if line.startswith('$GPGGA'):
            print('GPS GGA data:', line.strip())
        time.sleep(1)
except KeyboardInterrupt:
    print('Stopped reading GPS data.')
    ser.close()

Important Notes

Make sure your GPS module is connected to the correct serial pins on the Raspberry Pi.

GPS modules send data in NMEA format, which you can parse for useful info like latitude and longitude.

Sometimes GPS data may be empty or incomplete if the module has no satellite fix yet.

Summary

GPS modules send location data over serial connection in NMEA sentences.

Use Python's serial library to read and decode this data on Raspberry Pi.

Filter sentences like $GPGGA or $GPRMC to get useful GPS info.

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