GPS module data reading in Raspberry Pi - Step-by-Step Execution

Concept Flow - GPS module data reading

Start Program

↓

Initialize GPS Module

↓

Open Serial Port

↓

Read Data Line

↓

Parse NMEA Sentence

↓

Extract Coordinates

↓

Display or Store Data

↓

Repeat Reading

↩Back to Read Data Line

The program starts by setting up the GPS module and serial connection, then continuously reads and parses GPS data lines to extract location coordinates.

Execution Sample

Raspberry Pi

import serial
ser = serial.Serial('/dev/ttyUSB0', 9600)
line = ser.readline()
print(line.decode('ascii'))

This code opens the serial port to the GPS module, reads one line of data, and prints it as readable text.

Execution Table

Step	Action	Data Read	Parsed Result	Output
1	Open serial port /dev/ttyUSB0 at 9600 baud	-	-	-
2	Read one line from serial port	$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47	NMEA GPGGA sentence	-
3	Parse latitude from sentence	4807.038,N	48°07.038' N	-
4	Parse longitude from sentence	01131.000,E	11°31.000' E	-
5	Convert to decimal degrees	48°07.038' N, 11°31.000' E	48.1173, 11.5167	-
6	Print coordinates	-	-	Latitude: 48.1173, Longitude: 11.5167
7	Repeat reading next line	-	-	-
8	Stop reading	-	-	Program ends or interrupted

💡 Program stops when user interrupts or no more data is available

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
ser	None	Serial('/dev/ttyUSB0', 9600)	Serial('/dev/ttyUSB0', 9600)	Serial('/dev/ttyUSB0', 9600)	Serial('/dev/ttyUSB0', 9600)	Serial('/dev/ttyUSB0', 9600)
line	None	$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47	$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47	$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47	$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47	Next line or None
latitude_raw	None	None	4807.038,N	4807.038,N	4807.038,N	None or new value
longitude_raw	None	None	None	01131.000,E	01131.000,E	None or new value
latitude_dec	None	None	None	None	48.1173	48.1173 or updated
longitude_dec	None	None	None	None	11.5167	11.5167 or updated

Key Moments - 3 Insights

Why do we decode the line from bytes to ASCII before printing?

The serial port reads data as bytes, which are not readable text. Decoding converts bytes to a string so we can see the GPS data clearly, as shown in step 2 of the execution_table.

How do we know which part of the GPS data line contains latitude and longitude?

The GPS data uses a standard format called NMEA sentences. In the example, latitude is the third and fourth parts, longitude is the fifth and sixth. This is shown in steps 3 and 4 where we extract those parts.

Why convert coordinates from degrees and minutes to decimal degrees?

Decimal degrees are easier to use in calculations and mapping software. Step 5 shows this conversion from the raw format to decimal degrees.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the raw latitude data extracted?

A 01131.000,E

B 4807.038,N

C $GPGGA,123519

D 48.1173

💡 Hint

Check the 'Data Read' and 'Parsed Result' columns at step 3 in the execution_table.

At which step does the program convert coordinates to decimal degrees?

A Step 2

B Step 6

C Step 5

D Step 4

💡 Hint

Look for the step where 'Convert to decimal degrees' appears in the 'Action' column.

If the serial port was opened with the wrong device name, what would happen in the execution_table?

A Step 1 would fail to open serial port

B Step 2 would read data normally

C Step 6 would print coordinates

D Step 5 would convert coordinates

💡 Hint

Refer to step 1 where the serial port is opened; if device is wrong, it cannot open.

Concept Snapshot

GPS Module Data Reading:
- Open serial port to GPS device (e.g., /dev/ttyUSB0)
- Read NMEA sentences line by line
- Parse latitude and longitude from sentences
- Convert coordinates to decimal degrees
- Use or display coordinates
- Repeat reading continuously

Full Transcript

This visual execution shows how a Raspberry Pi reads data from a GPS module. First, the program opens the serial port connected to the GPS device. Then it reads one line of data, which is a NMEA sentence containing GPS info. The program extracts latitude and longitude parts from this sentence. Next, it converts these coordinates from degrees and minutes format to decimal degrees for easier use. Finally, it prints the coordinates. This process repeats to keep updating location data. Key points include decoding bytes to text, knowing where latitude and longitude are in the data, and converting formats for usability.

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