Appendix N: GNSS Satellite Monitoring Code (ZED-F9P)
# Displays position, heading, and satellites used in solution

from serial import Serial
from serial.tools import list_ports
from datetime import datetime, timezone
from pyubx2 import UBXReader, UBXMessage

def auto_deg(v):
return (v * 1e-7) if v else None

def auto_alt(v):
return (v / 1000.0) if v else None

def auto_heading(rh, ah):
if rh is None:
return None, None
heading = (rh * 1e-5 - 90.0) % 360
acc = ah * 1e-5 if ah else None
return heading, acc

def parse_nmea(raw):
if raw and raw[:1] == b”$”:
try:
return raw.decode(“ascii”, errors=”ignore”).strip()
except:
return None
return None

def parse_gsa(line):
parts = line.split(“,”)
return {p.split(“*”)[0] for p in parts[3:15] if p}

def parse_gsv(line):
parts = line.split(“,”)
sats = []
i = 4
while i + 3 < len(parts):
prn = parts[i]
elev = parts[i+1]
azim = parts[i+2]
snr = parts[i+3].split(“*”)[0]
if prn:
sats.append((prn, elev, azim, snr))
i += 4
return sats

def stream_status(port=”COM6”, baud=38400):

with Serial(port, baud, timeout=1.0) as s:  
    ubr \= UBXReader(s, protfilter=7)

    used \= set()  
    sats \= {}  
    heading \= None  
    acc \= None

    while True:

        raw, msg \= ubr.read()

        \# Ignore RTCM  
        if raw and raw\[:1\] \== b"\\xD3":  
            continue

        \# \---------- NMEA \----------  
        line \= parse\_nmea(raw)

        if line:  
            if "GSA" in line:  
                used \= parse\_gsa(line)

            elif "GSV" in line:  
                for prn, elev, azim, snr in parse\_gsv(line):  
                    sats\[prn\] \= (elev, azim, snr)

            print("\\n\[SATELLITES\]")  
            for prn in sorted(sats):  
                elev, azim, snr \= sats\[prn\]  
                flag \= "USED" if prn in used else "----"  
                print(f"PRN {prn:\>3}  {flag}  SNR={snr}  elev={elev}  az={azim}")

        \# \---------- UBX \----------  
        if isinstance(msg, UBXMessage):

            if msg.identity \== "NAV-RELPOSNED" and msg.relPosValid:  
                heading, acc \= auto\_heading(msg.relPosHeading, msg.accHeading)

            if msg.identity \== "NAV-PVT":

                t \= datetime(  
                    msg.year, msg.month, msg.day,  
                    msg.hour, msg.min, msg.second,  
                    tzinfo=timezone.utc  
                )

                lat \= auto\_deg(msg.lat)  
                lon \= auto\_deg(msg.lon)  
                alt \= auto\_alt(msg.height)

                print("\\n--- GPS FIX \---")  
                print("UTC Time :", t)  
                print("Latitude :", lat)  
                print("Longitude:", lon)  
                print("Altitude :", alt)

                if heading is not None:  
                    print(f"Heading  : {heading:.2f}° ±{acc:.2f}°")

if __name__ == “__main__”:

print("Available ports:")  
for p in list\_ports.comports():  
    print(f" \- {p.device}")

stream\_status("COM6", 38400\)