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.