def show_nearby_devices(lat, lon, r, n):
"""
Return nearby devices.
Arguments:
lat - Latitude in degrees
lon - Longitude in degrees
r - Search radius in km
n - output list length limit
"""
user_location = Location(lon=lon, lat=lat).to_wkt()
distance = ST_Distance_Sphere(Device.location_wkb, user_location) / 1000
direction = func.degrees(func.ST_Azimuth(user_location, Device.location_wkb))
devices = session.query(Device,
direction.label('direction'),
distance.label('distance')).filter(distance < r).order_by(distance.asc()).limit(n).all()
if not len(devices):
raise NoResultFound
return list(map(lambda device: {'device': device.Device.as_dict(),
'direction': round(device.direction, 2),
'distance': round(device.distance, 3)}, devices))
def trajectDirection(self):
"""traject direction of previous location and current location"""
azimuth = func.ST_Azimuth(func.lag(self.rawlocation).over(order_by=(self.device_info_serial, self.date_time,)), self.rawlocation)
return func.round(cast(func.degrees(azimuth), Numeric()), 2).label('tdirection')