You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
62 lines
2.3 KiB
62 lines
2.3 KiB
4 years ago
|
# Decode GPS data - Virtual IoT Hardware and Raspberry Pi
|
||
|
|
|
||
|
|
In this part of the lesson, you will decode the NMEA messages read from the GPS sensor by the Raspberry Pi or Virtual IoT Device, and extract the latitude and longitude.
|
||
|
|
|
||
|
|
## Decode GPS data
|
||
|
|
|
||
|
|
Once the raw NMEA data has been read from the serial port, it can be decoded using an open source NMEA library.
|
||
|
|
|
||
|
|
### Task - decode GPS data
|
||
|
|
|
||
|
|
Program the device to decode the GPS data.
|
||
|
|
|
||
|
|
1. Open the `gps-sensor` app project if it's not already open
|
||
|
|
|
||
|
|
1. Install the `pynmea2` Pip package. This package has code for decoding NMEA messages.
|
||
|
|
|
||
|
|
```sh
|
||
|
|
pip3 install pynmea2
|
||
|
|
```
|
||
|
|
|
||
|
|
1. Add the following code to the imports in the `app.py` file to import the `pynmea2` module:
|
||
|
|
|
||
|
|
```python
|
||
|
|
import pynmea2
|
||
|
|
```
|
||
|
|
|
||
|
|
1. Replace the contents of the `print_gps_data` function with the following:
|
||
|
|
|
||
|
|
```python
|
||
|
|
msg = pynmea2.parse(line)
|
||
|
|
if msg.sentence_type == 'GGA':
|
||
|
|
lat = pynmea2.dm_to_sd(msg.lat)
|
||
|
|
lon = pynmea2.dm_to_sd(msg.lon)
|
||
|
|
|
||
|
|
if msg.lat_dir == 'S':
|
||
|
|
lat = lat * -1
|
||
|
|
|
||
|
|
if msg.lon_dir == 'W':
|
||
|
|
lon = lon * -1
|
||
|
|
|
||
|
|
print(f'{lat},{lon} - from {msg.num_sats} satellites')
|
||
|
|
```
|
||
|
|
|
||
|
|
This code will use the `pynmea2` library to parse the line read from the UART serial port.
|
||
|
|
|
||
|
|
If the sentence type of the message is `GGA`, then this is a position fix message, and is processed. The latitude and longitude values are read from the message and converted to decimal degrees from the NMEA `(d)ddmm.mmmm` format. The `dm_to_sd` function does this conversion.
|
||
|
|
|
||
|
|
The direction of the latitude is then checked, and if the latitude is south, then the value is converted to a negative number. Same with the longitude, if it is west then it is converted to a negative number.
|
||
|
|
|
||
|
|
Finally the coordinates are printed to the console, along with the number of satellites used to get the location.
|
||
|
|
|
||
|
|
1. Run the code. If you are using a virtual IoT device, then make sure the CounterFit app is running and the GPS data is being sent.
|
||
|
|
|
||
|
|
```output
|
||
|
|
pi@raspberrypi:~/gps-sensor $ python3 app.py
|
||
|
|
47.6423109,-122.1390293 - from 3 satellites
|
||
|
|
```
|
||
|
|
|
||
|
|
> 💁 You can find this code in the [code-gps-decode/virtual-device](code-gps-decode/virtual-device) folder, or the [code-gps-decode/pi](code-gps-decode/pi) folder.
|
||
|
|
|
||
|
|
😀 Your GPS sensor program with data decoding was a success!
|