gpsModule.py

import time
import socketio
import json
import datetime
from gps import *

import obdUtils

#see https://gpsd.gitlab.io/gpsd/gpsd_json.html for more details on getting data from gpsd

SENSOR_TYPE = 'GPS'
ERROR = 'ERR'
INFO = 'INFO'
RETRY_INTERVAL = 1 #Delay in seconds when retrying to connect to node server


LATITUDE_DEC_PLACES = 5
LONGITUDE_DEC_PLACES = 5
SPEED_DEC_PLACES = 2
FT_DEC_PLACES = 2
MPH_MULTIPLIER = 2.2369 #when converting kph to mph
FT_MULTIPLIER = 3.28084 #when converting meters to feet

GPS_STATUSES = { #dict key value pair of possible gps status from NMEA TPV object
    0: 'Unknown',
    1: 'Normal',
    2: 'DGPS',
    3: 'RTK Fixed',
    4: 'RTK Floating',
    5: 'DR',
    6: 'GNSSDR',
    7: 'Time (surveyed)',
    8: 'Simulated',
    9: 'P(Y)'
}
    
DELAY = 1 #gps polling interval in seconds. Max polling rate 10hz for Adafruit Ultimate GPS (MTK3339 chipset)
gpsd = gps(mode=WATCH_ENABLE|WATCH_NEWSTYLE) 

sio = None

numTries = 1

def emitGpsData():
    while True:
        time.sleep(DELAY)
     
        try:
            report = gpsd.next()

            if report['class'] == 'TPV': #time-position-velocity report object
                data = {
                    'fixType': GPS_STATUSES[getattr(report,'status','')],
                    'latitude': obdUtils.formatDecimalPlaces(getattr(report,'lat',0.0), LATITUDE_DEC_PLACES),
                    'longitude': obdUtils.formatDecimalPlaces(getattr(report,'lon',0.0), LONGITUDE_DEC_PLACES),
                    'time': getattr(report,'time',''), #Time/date stamp in ISO8601 format, UTC. May have a fractional part of up to .001sec precision. May be absent if the mode is not 2D or 3D.
                    'altitude': getattr(report,'alt','nan'),#Altitude, height above ellipsoid, in meters. Probably WGS84.
                    'speed': obdUtils.formatDecimalPlaces((getattr(report,'speed',0.0) * MPH_MULTIPLIER), SPEED_DEC_PLACES), #mph converted from meters per second
                    'climb': getattr(report,'climb','nan'), #Climb (positive) or sink (negative) rate, meters per second.
                    'latitudeErr': getattr(report,'epy','nan'), #Latitude error estimate in meters. Certainty unknown.
                    'longitudeErr': getattr(report,'epx','nan'), #Longitude error estimate in meters. Certainty unknown.
                    'timeErr': getattr(report,'ept','nan'), #Estimated time stamp error in seconds. Certainty unknown.
                    'altitudeErr': getattr(report,'epv','nan'), #Estimated vertical error in meters. Certainty unknown.
                    'speedErr': obdUtils.formatDecimalPlaces((getattr(report,'eps',0.0) * MPH_MULTIPLIER), SPEED_DEC_PLACES),#Estimated speed error in meters per second. Certainty unknown.
                    'climbErr': getattr(report,'epc', 'nan') #Estimated climb error in meters per second. Certainty unknown.
                }
                #print(data)
                sio.emit('gpsData', json.dumps(data))
                
        except Exception as ex: #logs any errors encountered during reading of gps. Also allows program to pick back up if node server connection is lost
            errorLog = obdUtils.createLogMessage(ERROR, SENSOR_TYPE, type(ex).__name__, ex.args)
            print(errorLog)
            sio.emit('log', json.dumps(errorLog)) #will only work if exception is unrelated to node server connection
            continue



while True: #loop until a connection is made with the server instead of immediately exiting
    try:
        sio = socketio.Client()
        sio.connect('http://localhost:3000')
        emitGpsData() #temp workaround. Originally not needed. Seems to be issue with nodejs socketio version not sending connect packet to trigger connect() event
        break
        
    except Exception as ex:
        numTries += 1
        print("GPS app unable to connect to node server, retrying attempt {0}".format(numTries))
        time.sleep(RETRY_INTERVAL)
            
        continue


@sio.event
def connect():
    
    connectedLog = obdUtils.createLogMessage(INFO, SENSOR_TYPE, 'Connection', 'Established')
    print(connectedLog)
    sio.emit('log', json.dumps(connectedLog))
    
    emitGpsData()