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62 lines
2.3 KiB
62 lines
2.3 KiB
# Decode GPS data - Virtual IoT Hardware and Raspberry Pi
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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.
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## Decode GPS data
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Once the raw NMEA data has been read from the serial port, it can be decoded using an open source NMEA library.
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### Task - decode GPS data
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Program the device to decode the GPS data.
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1. Open the `gps-sensor` app project if it's not already open
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1. Install the `pynmea2` Pip package. This package has code for decoding NMEA messages.
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```sh
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pip3 install pynmea2
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```
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1. Add the following code to the imports in the `app.py` file to import the `pynmea2` module:
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```python
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import pynmea2
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```
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1. Replace the contents of the `print_gps_data` function with the following:
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```python
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msg = pynmea2.parse(line)
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if msg.sentence_type == 'GGA':
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lat = pynmea2.dm_to_sd(msg.lat)
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lon = pynmea2.dm_to_sd(msg.lon)
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if msg.lat_dir == 'S':
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lat = lat * -1
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if msg.lon_dir == 'W':
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lon = lon * -1
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print(f'{lat},{lon} - from {msg.num_sats} satellites')
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```
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This code will use the `pynmea2` library to parse the line read from the UART serial port.
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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.
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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.
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Finally the coordinates are printed to the console, along with the number of satellites used to get the location.
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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.
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```output
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pi@raspberrypi:~/gps-sensor $ python3 app.py
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47.6423109,-122.1390293 - from 3 satellites
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```
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> 💁 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.
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😀 Your GPS sensor program with data decoding was a success!
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