Linking GNSSNTRIPClient and RTCMReader using in-memory stream with BytesIO

[dgashby]

Hi,
I'm trying to create an in-memory stream to pass messages on to an RTCMReader using the following:

ntrip_rtcm_stream = io.BytesIO(b"")

rtr = RTCMReader(ntrip_rtcm_stream)

gnc = GNSSNTRIPClient()
gnc.run(
    server=NTRIP_SERVER,
    port=NTRIP_PORT,
    https=0,
    mountpoint=NTRIP_MOUNTPOINT,
    datatype="RTCM",
    ntripuser=NTRIP_USER,
    ntrippassword=NTRIP_PASSWORD,
    ggainterval=-1,
    output=ntrip_rtcm_stream,
    verbosity=2,
)
    while True:
        try:                                                                                                                       
            raw, msg = rtr.read()
	    if msg is not None:
                log.info("RTCM:" + msg)

I'm seeing the verbose logging from within the GNSSNTRIPClient to indicate various message types are being received from the NTRIP server, however rtr.read() doesn't seem to be reading anything. When I strip out the RTCMReader and just try to read the ntrip_rtcm_stream it doesn't return any bytes either. If I replace the BytesIO stream with an actual file, it does have RTCM data written to it.

Any ideas why the in-memory stream isn't working for me?

Thanks,

Dean

[semuadmin]

Hi @dgashby,

Couple of issues with the code...

1. Not sure BytesIO can be used in quite this way e.g. consider the following:

from io import BytesIO

b = BytesIO(b"1234")
print(b.getvalue())  # outputs b'1234'
print(b.read(2))  # outputs b'12'
print(b.read(2))  # outputs b'34'
print(b.read())  # outputs b''

b.write(b"5678")
print(b.getvalue())  # outputs b'12345678'
print(b.read())  # still outputs b''

2. As per the API documentation, the GNSSNTRIPClient output argument supports the following specific writeable output media classes (intended to cover the most common use cases):

- BufferedWriter e.g. binary file, for raw data bytes
- TextIOWrapper e.g. text file, for parsed data as a string
- Serial e.g. a GNSS receiver's UART or USB port
- Socket e.g. to broadcast to a local TCP/IP network
- Queue e.g. for asynchronous processing in a separate thread

For a more flexible approach, I recommend you take a look at the ntrip_client_generic.py example in the \examples folder. You can substitute the simple print() statement in the datathread with whatever you want to do with the raw or parsed RTCM data you receive.

Hope this helps.

[dgashby]

Thank you for the quick response. I had not noticed ntrip_client_generic.py, it looks like using a Queue combined with a separate thread to clear the queue will solve my problem. Very much appreciate your help.