get data from gnssstreamer_cli via socket

[duemchen]

I like to run gnssstreamer_cli as a service later.
On the same machine runs my service (on a rover) in python.
Now i need the positions data online on the simplest way from gnssstreamer_cli.
I have tested socket:

If I want data via Socket, i must use
gnssstreamer_cli with options --clioutput 3 --format 2 --output 127.0.0.1:2000
data receive in my clientsocket in raw:
[127.0.0.1] $GNGGA,141338.00,5306.38795,N,01253.68096,E,4,12,0.96,58.9,M,42.0,M,2.0,4095*55

only format 2 runs. Other formats not able?
I need lat lon fix age
How can i convert to formats like this or json?

lat: 53.1064656667, lon: 12.8946828333, alt: 58.9, fix: RTK FIXED, corr age: 37.0

It runs in lambda example:
--clioutput 4
--output "lambda msg: print(f'lat: {msg.lat}, lon: {msg.lon}, alt: {msg.alt}, fix: {['NO FIX','2D','3D','N/A','RTK FIXED','RTK FLOAT'][msg.quality]},

I need the positions data online on the simplest way from gnssstreamer_cli in a "good" format.
Must not be socket!

[semuadmin]

Hi @duemchen

So if you want to run gnssstreamer as a socket server, you can choose any output format you want (including json), e.g. this will run fine:

gnssstreamer -P /dev/tty.usbmodem101 --cliout 3 --output localhost:50011 --verbosity 2 --format 32

However, if you also want to run gnsstreamer as a socket client, the output format must be binary (--format 2) because that's all the underlying GNSS parsers are designed to handle. If you want to use a different format, you will need to write your own socket client to handle that format, which is non-trivial.

You need to clarify what exactly you mean by "online in the simplest way", but I don't think gnssstreamer is what you're after. I suspect you're probably looking at some kind of HTTP server solution which can be consumed by a web browser or REST API.

There is, as it happens, an example Python script of just such a thing here:

https://github.com/semuconsulting/pynmeagps/tree/master/examples/webserver

It's only a simple illustration - I certainly wouldn't use it for any mission-critical application! - but in essence you execute the script as follows:

python3 nmeaserver.py ipaddress=localhost ipport=8080 serport="/dev/tty.usbmodem101" baudrate=38400 timeout=0.1

If you then enter an address of http://localhost:8080 in your web browser, you will see a web page that looks something like this (this assumes your receiver is outputting standard NMEA RMC, GGA and GSA sentences):

The data will refresh automatically every 5 seconds. Does this look like the sort of thing that might meet your needs?

[duemchen]

Hello Steven,
thanks for the big answer. I think, my Problem is so simple, that you can't believe it.
"online" i only mean "just in time" with low delay.

I only need your fine RTK-FIXed Position Data receive in my Program. On the simplest way (Socket or other). Some Days before you have helped me and the data are fine in lambda print:

gnssstreamer --port /dev/ttyACM0 --baudrate 115200 --msgfilter "GNGGA" --cliinput 1 --input www.sapos-bb-ntrip.de:2101/VRS_3_2G_BB --rtkuser duemcxxxx --rtkpassword Hoxxxxx --rtkggaint 10 --clioutput 4 --output "lambda msg: print(f'lat: {msg.lat}, lon: {msg.lon}, alt: {msg.alt}, fix: {['NO FIX','2D','3D','N/A','RTK FIXED','RTK FLOAT'][msg.quality]}, corr age: {msg.diffAge}')" --verbosity 3 --logtofile /home/pi/log.txt

lat: 53.1064658333, lon: 12.8946826667, alt: 58.9, fix: RTK FIXED, corr age: 2.0

With my Socket client also this runs,

gnssstreamer --port /dev/ttyACM0 --baudrate 115200 --msgfilter "GNGGA" --cliinput 1 --input www.sapos-bb-ntrip.de:2101/VRS_3_2G_BB --rtkuser duemcxxxx --rtkpassword Horxxxx --rtkggaint 10 --clioutput 3 --format 2 --output 127.0.0.1:2000 --verbosity 2

but only with format 2 i receive data:
[127.0.0.1] $GNGGA,141338.00,5306.38795,N,01253.68096,E,4,12,0.96,58.9,M,42.0,M,2.0,4095*55

My socket connects with gnsstreamer in all formats.
But format 32 and all other sends no data to my socket.

The client socket code is simple. Can you see my mistake?

import socket
ip = '127.0.0.1'
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((ip, 2000))
try:
while True:
antwort = s.recv(1024)
print("[{}] {}".format(ip, antwort.decode()))
finally:
s.close()

[semuadmin]

Hi @duemchen

If only Python socket programming was as simple as that!

Your simple socket client assumes that the incoming GNSS data can be parsed ("decoded") using the decode() method, but that will only work in very limited circumstances:

1. decode only works for binary-encoded ascii text i.e. NMEA data sent in binary format (it wouldn't work for UBX or RTCM data, for example). As I mentioned earlier, if you use any other format, you need to substitute decode for a method which can parse that format, and that is non-trivial.
2. your client assumes that individual messages will always be less than 1024 bytes and that the message will always start at byte 0 - that may not necessarily be the case.

You could improve upon the visual representation of the NMEA data using e.g. more complex f-string or regex formatting, but there may be better approaches. Why not simply use binary format (--format 2) and let gnssstreamer act as your socket client and parser? You can then reformat the parsed data attributes (lat, lon, etc.) however you like.

If you're determined to write your own socket client, I recommend you take another look at the Python documentation and code illustrations.

[duemchen]

ok. thanks

[semuadmin]

Ok Plan B 😀. Try the following modified code for your socket client. GNSSReader uses a utility class called SocketWrapper, which basically allows it to treat a socket connection like any other serial or file stream:

import socket
from pygnssutils import GNSSReader

ip = '127.0.0.1'
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((ip, 2000))
gnr = GNSSReader(s)
for raw, parsed in gnr:
    if raw is not None:
        if parsed.identity == "GNGGA":
            print(f"IP = {ip}, Lat = {parsed.lat}, Lon = {parsed.lon}, Hmsl = {parsed.alt}")

You can easily adapt this to use other NMEA (or UBX, etc.) sentences and attributes.

TIP: If you're using this on a local LAN, I would recommend using a port number higher than 50000, as lower numbers may conflict with other network protocols.

[semuadmin]

If you want more information on these methods, refer to the API documentation:

https://www.semuconsulting.com/pynmeagps/pynmeagps.html#module-pynmeagps.socketwrapper
https://www.semuconsulting.com/pygnssutils/pygnssutils.html#module-pygnssutils.gnssreader

[duemchen]

Wow! That help is, what I need !!! it runs. Now I can complete my program.
Thank you very much.