After some tinkering I was able to cook up some Python code to get the GPS data. So, a Magellan Meridian Gold GPS is connected over the serial port to a PC running Windows XP and Python. The Python version I am using is 2.52 and if you want to play with the code you may want to install the pySerial library before starting.
First, here is the result—cut & paste—from Python Shell.
<?xml version="1.0" encoding="UTF-8"?> <event> <head> <id>91ce7524-3336-4619-a9a0-e8ee32d2f609</id> <type>GPS</type> <time_stamp>2008-12-30T20:19:31Z</time_stamp> <entity>DS_GPS_001</entity> </head> <body> <latitude>43 38.8317 N</latitude> <longitude>079 23.8942 W</longitude> <speed>00.0</speed> <course>000.0</course> <valid>True</valid> </body> </event>
<?xml version="1.0" encoding="UTF-8"?> <event> <head> <id>aed3e5b7-f98a-49d1-b950-4434331df8ae</id> <type>GPS</type> <time_stamp>2008-12-30T20:19:42Z</time_stamp> <entity>DS_GPS_001</entity> </head> <body> <latitude>43 38.8289 N</latitude> <longitude>079 23.8965 W</longitude> <speed>00.0</speed> <course>000.0</course> <valid>True</valid> </body> </event>
The program reads the serial port every 10-12 seconds, extracts the position and speed data from a $GPRMC message and packages the data into XML form of an event object.
The Python code has two modules (files), the first one— gps_event_template.py —contains only a template for XML and JSON strings; the main module— gps_event.py —has all the working code.
The template has placeholders—like $time_stamp_here$ —which are simply later replaced by GPS data.
""" gps_event_template.py XML & JSON templates for GPS event """ def xml_template(): """<?xml version="1.0" encoding="UTF-8"?> <event> <head> <id>$id_here$</id> <type>$type_here$</type> <time_stamp>$time_stamp_here$</time_stamp> <entity>$entity_here$</entity> </head> <body> <latitude>$latitude_here$</latitude> <longitude>$longitude_here$</longitude> <speed>$speed_here$</speed> <course>$course_here$</course> <valid>$valid_here$</valid> </body> </event> """ def json_template(): """{ "event":{ "head":{"id":"$id_here$", "type":"$type_here$", "time_stamp":"$time_stamp_here$", "entity":"$entity_here$" }, "body":{"latitude":"$latitude_here$", "longitude":"$longitude_here$", "speed":"$speed_here$", "course":"$course_here$", "valid":"$valid_here$" } } } """ def compress_template(s): """ Compress XML or JSON template """ rli = {'{ ':'{', ' }':'}', ', "':',"', '> <':'><'} st = ' '.join(s.split()) for (k, v) in rli.items(): st = st.replace(k, v) return st if __name__ == "__main__": print xml_template.__doc__ print json_template.__doc__ print compress_template(xml_template.__doc__) print compress_template(json_template.__doc__)
Here is the main module; if running from Python Shell, start this one. Python is an easy read, so you should not have trouble following. The sendToCep(xst) function simply prints the XML to the Shell; I need to tinker with the CEP server before implementing this one. Keep in mind that this is a blog-as-you-go project.
"""
gps_event.py
Reads position and speed data from Magellan Meridian Gold GPS
--connected on COM 1-- every 10-12 seconds.
Packages GPS data into XML and sends to a CEP server.
"""
from datetime import datetime
import time
import serial
import uuid
import gps_event_template
import gps_aws
ser = serial.Serial()
ser_mode = True
sample_delay = 10
msg_cnt = 1
obj = {'id':'','type':'GPS','time_stamp':'','entity':'DS_GPS_001',
'latitude':'', 'longitude':'','speed':'', 'course':'', 'valid':''}
def gps_main():
""" Read GPS every 10-12 seconds, send XML to CEP """
(ser.port, ser.baudrate, ser.timeout) = (0, 4800, 4)
ser.open()
try:
while 1:
st = readGps()
if st:
sendToCep(st)
else:
# break
pass
time.sleep(sample_delay)
finally:
ser.close()
return '*** ABORTING gps_event.py ***'
def readGps():
""" Read GPS, create XML if valid reading """
global ser_mode
ser.flushInput()
li = readCom(ser_mode)
if li[0] == '$GPRMC':
obj['id'] = str(uuid.uuid4())
parseGpsData(li)
st = makeOutputString(fmt = 'X', pretty = 0)
else:
st = None
return st
def makeOutputString(fmt = 'X', pretty = 0):
""" Make XML or JSON string """
if fmt == 'J':
st = gps_event_template.json_template.__doc__
else:
st = gps_event_template.xml_template.__doc__
if pretty == 0:
st = gps_event_template.compress_template(st)
for (k,v) in obj.items():
st = st.replace('$%s_here$'%(k,), v)
return st
def parseGpsData(li):
""" Parse GPS list to object """
obj['time_stamp'] = make_ts(li[1],li[9])
obj['latitude'] = make_ll(li[3],li[4])
obj['longitude'] = make_ll(li[5],li[6])
obj['course'] = li[8]
obj['speed'] = li[7]
obj['valid'] = 'True' if li[2] == 'A' else 'False'
def readCom(sm = False):
""" Read COM port, split GPS string to a list """
(i, st) = (0, ['?'])
while (i < 25):
i = i + 1
if sm:
ln = ser.readline()
else:
ln = "$GPRMC,172021.20,A,4338.8243,N,"
ln = ln + "07923.9149,W,00.0,000.0,291208,11,W*48"
if ln:
s1 = ln.split(",")
# print s1
if s1[0] == '$GPRMC':
st = s1
break
return st
def make_ts(tim, dte):
""" Make time-stamp """
return datetime(int('20' + dte[4:]), int(dte[2:4]), int(dte [0:2]),
int(tim[0:2]), int(tim[2:4]), int(tim[4:6])).isoformat() + 'Z'
def make_ll(c, s):
""" Make lattitude and longitude """
i = len(c) - 7
return ' '.join([c[:i], c[i:], s])
def sendToCep(xst):
""" Send XML string to EP/CEP/BUS """
print xst # just print for now
if __name__ == "__main__":
print gps_main()
So the next step is a CEP server—install, configure, communicate, do something with.
To be continued.