Ntrip client not receiving RTCM corrections

Question

I'm searching for help understanding how to develope a complete and functional NTRIP Client in order to receive RTCM corrections. I'm using Python 3.4, for now on Windows 7. Searching the net, I found some sample code and I used it to write a basic client. The problem is... it doesn't work.

I have access to a rtk correction service. The service is active and functioning.

This is a snippet of my code.

dummyNMEA = "$GPGGA,143741.356,7839.493,S,07627.626,W,0,00,,,M,,M,,*45"

username = my_username    #username for RTCM correction service
password = my_password    #password for RTCM correction service
port = 2101    #port for the service

'''Generate an encoding of the username:password for the service.
The string must be first encoded in ascii to be correctly parsed by the
base64.b64encode function.'''
pwd = base64.b64encode("{}:{}".format(username, password).encode('ascii'))

#The following decoding is necessary in order to remove the b' character that
#the ascii encoding add. Othrewise said character will be sent to the net and misinterpreted.
pwd = pwd.decode('ascii')

print("Header sending... \n")

header =\
"GET /mountpoint HTTP/1.1\r\n" +\
"Host my_host\r\n" +\
"Ntrip-Version: Ntrip/1.0\r\n" +\
"User-Agent: ntrip.py/0.1\r\n" +\
"Accept: */*" +\
"Connection: close\r\n" +\
"Authorization: Basic {}\r\n\r\n".format(pwd)

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((my_host,int(port)))
s.send(header.encode('ascii'))

print("Waiting answer...\n")
data = s.recv(2048).decode('ascii')
print(data)

s.send(dummyNMEA.encode('ascii'))
data = s.recv(2048).decode('ascii')
print(data)

s.close()

Now, the code is partially funcitoning. The request goes to the rtk server and I am correctly authenticated. I receive the correct answer as from ntrip protocol:

ICY 200 OK Server: "Server of the mountpoint" Date: "The date"

After this, I have to send a NMEA GGA sentence, in order to start receiving the RTCM corrections. I created various dummy NMEA sentences with a generator and tested sending them. I send the sentence and.... nothing happens. I receive no answer from the server.

Somebody has some idea? Perhaps I do something wrong when encoding the sentence?

I read that perhaps I should send the NMEA sentence continuosly, but I'm new in Python programming and I am not sure how to do that with sockets.

English is not my mother language, so please excuse my errors :)

Thnak you everyone.

Answer 1

You need to add '\r\n' to the end of the NMEA string.

dummyNMEA = "$GPGGA,143741.356,7839.493,S,07627.626,W,0,00,,,M,,M,,*45\r\n"

Answer 2

You have to create an Header for the NMEA as well.

dummyHeader = \
        "Ntrip-GGA: {}\r\n".format(dummyNMEA)

Then you should get an answer.

Answer 3

When you are sending the GGA is it a position that has coverage on your rtk correction service? I have done this before, sent dummy positions that are outside the network coverage and nothing was returned, not even an error message, just no corrections.

Cheers, Steve.