Run a GNSS NMEA TCP/IP server for mocking your location on an Android device (with RTK support)

grey-panda-nmea-server.py

#!/usr/bin/env python

# plug in grey panda
# open Lefebure NTRIP Client android app
# configure it:
# - Receiver Settings -> External via TCP/IP (enter the IP of the machine running this script and port 3001)
# - Receiver Settings -> GPS Mock Locations (check checkbox)
# - NTRIP Settings -> Caster IP/Port/Username Password for your local RTK network
# - NTRIP Settings -> Data Stream needs to be an RTCM3 source
# go into android developer settings and select the Lefebure NTRIP Client app to use for mock locations
# go into android location settings and switch the mode to Device only
# fire up this script (should say waiting for connection)
# connect in the Lefebure NTRIP Client app (should start with GPS fix type, then switch to DGPS then RTK)

import os
import time
import sys
import struct
import traceback 
import socket

from panda import Panda, PandaSerial

TCP_ADDR = "0.0.0.0"
TCP_PORT = 3001

CLASS_CFG = 0x06
MSG_CFG_DGNSS = 0x70

def ubx_checksum(data):
  #cs = 0
  ck_a = 0
  ck_b = 0
  for i in data:
    ck_a = (ck_a + ord(i)) & 0xFF
    ck_b = (ck_b + ck_a) & 0xFF
  return (ck_a, ck_b)
  
def add_ubx_checksum(msg):
  (ck_a, ck_b) = ubx_checksum(msg[2:])
  return msg + struct.pack('<BB', ck_a, ck_b)

def add_nmea_checksum(msg):
  d = msg[1:]
  cs = 0
  for i in d:
    cs ^= ord(i)
  return msg + "*%02X" % cs

if __name__ == "__main__":
  panda = Panda()
  ser = PandaSerial(panda, 1, 9600)

  # power cycle by toggling reset
  print "resetting"
  panda.set_esp_power(0)
  time.sleep(0.5)
  panda.set_esp_power(1)
  time.sleep(0.5)
  print "done"
  ser.read(1024)

  # upping baud rate
  baudrate = 460800

  print "upping baud rate"
  msg = add_nmea_checksum("$PUBX,41,1,0039,0003,%d,0" % baudrate)+"\r\n"
  print msg
  ser.write(msg)
  time.sleep(0.1)   # needs a wait for it to actually send

  # new panda serial
  ser = PandaSerial(panda, 1, baudrate)

  print "configure RTK"
  payload = struct.pack('<BBBB', 3, 0, 0, 0)
  header = struct.pack('<BBBBH', 0xb5, 0x62, CLASS_CFG, MSG_CFG_DGNSS, len(payload))
  msg = add_ubx_checksum(header + payload)
  ser.write(msg)

  while 1:
    try:
      # start tcp server and wait for connection
      print 'waiting for connection...'
      s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
      s.bind((TCP_ADDR, TCP_PORT))
      s.listen(1)
      conn, addr = s.accept()
      print 'connection address:', addr

      while True:
        nmea = ser.read(1024)
        if len(nmea) > 0:
          conn.send(nmea)
          sys.stdout.write(nmea)
          sys.stdout.flush()
          #print str(ret).encode("hex")

        try:
          conn.settimeout(0.1)
          rtcm = conn.recv(16)
          while len(rtcm) > 0:
              ser.write(rtcm)
              #print str(rtcm).encode('hex')
              rtcm = conn.recv(16)
          conn.settimeout(None)
        except socket.timeout:
          pass
    except KeyboardInterrupt:
      print 'shutting down ...'
      panda.close()
      conn.shutdown(socket.SHUT_RDWR)
      conn.close()
      sys.exit()
    except:
      print traceback.format_exc()
      time.sleep(2)