maglink-console/rtcm_208_capture.py

#!/usr/bin/env python3
"""
Capture raw RTCM message 208 to binary file for manual analysis.
"""
import base64
import socket
import time
from datetime import datetime


# NTRIP configuration
CASTER_HOST = "truertk.pointonenav.com"
CASTER_PORT = 2101
MOUNTPOINT = "AUTO"
USERNAME = "9t7fwfbm57"
PASSWORD = "96m7bec9g8"

LAT = 36.1140884
LON = -97.0880663
ALT = 390.0


def build_gga(lat: float, lon: float, alt: float) -> bytes:
    """Build NMEA GGA sentence."""
    now_utc = datetime.utcnow().strftime("%H%M%S")
    lat_hemi = "N" if lat >= 0 else "S"
    lat_abs = abs(lat)
    lat_deg = int(lat_abs)
    lat_min = (lat_abs - lat_deg) * 60.0
    lat_str = f"{lat_deg:02d}{lat_min:07.4f}"

    lon_hemi = "E" if lon >= 0 else "W"
    lon_abs = abs(lon)
    lon_deg = int(lon_abs)
    lon_min = (lon_abs - lon_deg) * 60.0
    lon_str = f"{lon_deg:03d}{lon_min:07.4f}"

    fields = ["GPGGA", now_utc, lat_str, lat_hemi, lon_str, lon_hemi, "1", "12", "1.0", f"{alt:.1f}", "M", "", "M", "", ""]
    core = ",".join(fields)
    checksum = 0
    for char in core:
        checksum ^= ord(char)
    return f"${core}*{checksum:02X}\r\n".encode("ascii")


def make_ntrip_request(host: str, port: int, mount: str, user: str, password: str) -> bytes:
    """Create NTRIP v2 HTTP request."""
    auth = base64.b64encode(f"{user}:{password}".encode("utf-8")).decode("ascii")
    req = (
        f"GET /{mount} HTTP/1.1\r\n"
        f"Host: {host}:{port}\r\n"
        f"Ntrip-Version: Ntrip/2.0\r\n"
        f"User-Agent: RTCM-Capture/1.0\r\n"
        f"Connection: close\r\n"
        f"Authorization: Basic {auth}\r\n\r\n"
    )
    return req.encode("ascii")


def main():
    timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
    output_file = f"rtcm_208_raw_{timestamp}.bin"
    index_file = f"rtcm_208_index_{timestamp}.txt"

    print(f"RTCM Message 208 Raw Capture")
    print(f"=" * 80)
    print(f"Caster: {CASTER_HOST}:{CASTER_PORT}/{MOUNTPOINT}")
    print(f"Output: {output_file}")
    print(f"Index:  {index_file}")
    print(f"Capturing for 60 seconds or 20 messages, whichever comes first...")
    print(f"=" * 80)
    print()

    last_gga_time = 0
    start_time = time.monotonic()
    msg_208_count = 0
    total_messages = 0

    try:
        # Connect
        print("Connecting...")
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.settimeout(30)
        sock.connect((CASTER_HOST, CASTER_PORT))
        sock.sendall(make_ntrip_request(CASTER_HOST, CASTER_PORT, MOUNTPOINT, USERNAME, PASSWORD))

        # Read headers
        header = b""
        while b"\r\n\r\n" not in header:
            chunk = sock.recv(1)
            if not chunk:
                print("ERROR: Connection closed")
                return
            header += chunk

        if "200 OK" not in header.decode("iso-8859-1", errors="replace"):
            print("ERROR: Connection failed")
            return

        print("Connected!\n")

        # Open output files
        with open(output_file, 'wb') as binfile, open(index_file, 'w') as idxfile:
            idxfile.write(f"# RTCM 208 Message Index\n")
            idxfile.write(f"# Captured: {datetime.now().isoformat()}\n")
            idxfile.write(f"# Format: message_number, offset, length, timestamp\n")
            idxfile.write(f"#\n")

            file_offset = 0

            # Receive loop
            while time.monotonic() - start_time < 60 and msg_208_count < 20:
                now = time.monotonic()

                # Send GGA every 10 seconds
                if now - last_gga_time >= 10:
                    sock.sendall(build_gga(LAT, LON, ALT))
                    elapsed = int(now - start_time)
                    print(f"[{elapsed:3d}s] Total: {total_messages}, Msg 208: {msg_208_count}/20")
                    last_gga_time = now

                # Receive data
                data = sock.recv(4096)
                if not data:
                    print("Connection closed")
                    break

                # Parse messages
                i = 0
                while i < len(data):
                    if data[i] == 0xD3 and i + 2 < len(data):
                        length = ((data[i+1] & 0x03) << 8) | data[i+2]
                        msg_total_len = 3 + length + 3

                        if i + msg_total_len <= len(data) and length >= 3:
                            msg_type = (data[i+3] << 4) | (data[i+4] >> 4)
                            total_messages += 1

                            if msg_type == 208:
                                msg_208_count += 1
                                msg_data = data[i+3:i+3+length]  # Just the payload

                                # Write to binary file
                                binfile.write(msg_data)
                                binfile.flush()

                                # Write to index
                                ts = datetime.now().isoformat()
                                idxfile.write(f"{msg_208_count},{file_offset},{length},{ts}\n")
                                idxfile.flush()

                                print(f"  ✓ Captured message 208 #{msg_208_count} - {length} bytes at offset {file_offset}")

                                file_offset += length

                            i += msg_total_len
                            continue
                    i += 1

    except KeyboardInterrupt:
        print("\n\nInterrupted by user")
    except Exception as e:
        print(f"\nERROR: {e}")
        import traceback
        traceback.print_exc()
    finally:
        if 'sock' in locals():
            try:
                sock.close()
            except:
                pass

    print(f"\n{'=' * 80}")
    print(f"CAPTURE COMPLETE")
    print(f"{'=' * 80}")
    print(f"Messages captured: {msg_208_count}")
    print(f"Output file: {output_file} ({file_offset} bytes)")
    print(f"Index file:  {index_file}")
    print()
    print("To view the binary file:")
    print(f"  hexdump -C {output_file}")
    print(f"  xxd {output_file}")
    print()
    print("To extract a specific message (e.g., message #1):")
    print("  1. Look up offset and length in index file")
    print("  2. Use: dd if={output_file} bs=1 skip=<offset> count=<length> | hexdump -C")


if __name__ == "__main__":
    main()