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GPS parsing module for CircuitPython. Meant to parse NMEA data from serial GPS modules.
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Fixed some errors travis was throwing.
Latest commit 98b8145 May 22, 2019

README.rst

Introduction

Documentation Status Discord Build Status

GPS parsing module. Can parse simple NMEA data sentences from serial GPS modules to read latitude, longitude, and more.

Dependencies

This driver depends on:

Please ensure all dependencies are available on the CircuitPython filesystem. This is easily achieved by downloading the Adafruit library and driver bundle.

Usage Example

See examples/gps_simpletest.py for a demonstration of parsing and printing GPS location.

Important: Feather boards and many other circuitpython boards will round to two decimal places like this:

>>> float('1234.5678')
1234.57

This isn't ideal for GPS data as this lowers the accuracy from 0.1m to 11m.

This can be fixed by using string formatting when the GPS data is output.

An implementation of this can be found in examples/gps_simpletest.py

import time
import board
import busio

import adafruit_gps

RX = board.RX
TX = board.TX

uart = busio.UART(TX, RX, baudrate=9600, timeout=30)

gps = adafruit_gps.GPS(uart, debug=False)

gps.send_command(b'PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')

gps.send_command(b'PMTK220,1000')

last_print = time.monotonic()
while True:

    gps.update()

    current = time.monotonic()
    if current - last_print >= 1.0:
        last_print = current
        if not gps.has_fix:
            print('Waiting for fix...')
            continue
        print('=' * 40)  # Print a separator line.
        print('Latitude: {0:.6f} degrees'.format(gps.latitude))
        print('Longitude: {0:.6f} degrees'.format(gps.longitude))

These two lines are the lines that actually solve the issue:

print('Latitude: {0:.6f} degrees'.format(gps.latitude))
print('Longitude: {0:.6f} degrees'.format(gps.longitude))

Note: Sending multiple PMTK314 packets with gps.send_command() will not work unless there is a substantial amount of time in-between each time gps.send_command() is called. A time.sleep() of 1 second or more should fix this.

About NMEA Data

This GPS module uses the NMEA 0183 protocol.

This data is formatted by the GPS in one of two ways.

The first of these is GGA. GGA has more or less everything you need.

Here's an explanation of GGA:

                                                    11
       1         2       3 4        5 6 7  8   9  10 |  12 13  14   15
       |         |       | |        | | |  |   |   | |   | |   |    |
$--GGA,hhmmss.ss,llll.ll,a,yyyyy.yy,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh
  1. Time (UTC)
  2. Latitude
  3. N or S (North or South)
  4. Longitude
  5. E or W (East or West)
  6. GPS Quality Indicator,
    • 0 - fix not available,
    • 1 - GPS fix,
    • 2 - Differential GPS fix
  7. Number of satellites in view, 00 - 12
  8. Horizontal Dilution of precision
  9. Antenna Altitude above/below mean-sea-level (geoid)
  10. Units of antenna altitude, meters
  11. Geoidal separation, the difference between the WGS-84 earth ellipsoid and mean-sea-level (geoid), "-" means mean-sea-level below ellipsoid
  12. Units of geoidal separation, meters
  13. Age of differential GPS data, time in seconds since last SC104 type 1 or 9 update, null field when DGPS is not used
  14. Differential reference station ID, 0000-1023
  15. Checksum

The second of these is RMC. RMC is Recommended Minimum Navigation Information.

Here's an explanation of RMC:

                                                           12
       1         2 3       4 5        6 7   8   9   10   11|
       |         | |       | |        | |   |   |    |   | |
$--RMC,hhmmss.ss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,xxxx,x.x,a*hh
  1. Time (UTC)
  2. Status, V = Navigation receiver warning
  3. Latitude
  4. N or S
  5. Longitude
  6. E or W
  7. Speed over ground, knots
  8. Track made good, degrees true
  9. Date, ddmmyy
  10. Magnetic Variation, degrees
  11. E or W
  12. Checksum

Info about NMEA taken from here.

Contributing

Contributions are welcome! Please read our Code of Conduct before contributing to help this project stay welcoming.

Building locally

To build this library locally, you'll need to install the circuitpython-build-tools package.

python3 -m venv .env
source .env/bin/activate
pip install circuitpython-build-tools

Once installed, make sure you are in the virtual environment:

source .env/bin/activate

Then run the build:

circuitpython-build-bundles --filename_prefix adafruit-circuitpython-gps --library_location .

Sphinx documentation

Sphinx is used to build the documentation based on rST files and comments in the code. First, install dependencies (feel free to reuse the virtual environment from above):

python3 -m venv .env
source .env/bin/activate
pip install Sphinx sphinx-rtd-theme

Now, once you have the virtual environment activated:

cd docs
sphinx-build -E -W -b html . _build/html

This will output the documentation to docs/_build/html. Open the index.html in your browser to view them. It will also (due to -W) error out on any warning like Travis will. This is a good way to locally verify it will pass.

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