The only thing left is an interface to the GPS library to bundle up it's use. The constructor takes a UART object and creates a GPS object with it. It also initializes instance variable in which to cache the GPS location data.
def __init__(self, uart):
self._gps = adafruit_gps.GPS(uart, debug=False)
self._latitude = 0
self._longitude = 0
Once an instance has been created, it is initialized using the begin method which configures the GPS object.
def begin(self):
self._gps.send_command(b'PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0')
self._gps.send_command(b'PMTK220,1000')
A big part of using GPS is getting a fix. I.e. locking onto signals from the satellites in view/range. No data can be fetched until that is done. The get_fix method takes care of waiting for a fix to be acquired. Once it has, True is returned. If an exception is raised, False is returned.
def get_fix(self):
try:
logger.debug('Calling gps update')
self._gps.update()
logger.debug('Back from gps update')
while not self._gps.has_fix:
# Try again if we don't have a fix yet.
logger.debug('Waiting for fix...')
time.sleep(0.1)
self._gps.update()
return True
except UnicodeError:
return False
The read method pulls data from the GPS and caches it. Corresponding properties return the cached data.
def read(self):
logger.debug('Reading GPS')
self._latitude = self._gps.latitude
self._longitude = self._gps.longitude
@property
def latitude(self):
return self._latitude
@property
def longitude(self):
return self._longitude
Notice that there's no attempt to re-establish a fix since we're only reading from the GPS once, when the system starts up.
Page last edited March 08, 2024
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