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brentperteet
288
rtcm_208_decoder.py
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288
rtcm_208_decoder.py
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#!/usr/bin/env python3
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"""
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Decoder for RTCM message 208 - appears to be ASCII/text based.
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Captures and displays message 208 content in multiple formats.
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"""
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import base64
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import socket
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import time
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import csv
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from datetime import datetime, timezone
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# NTRIP configuration
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CASTER_HOST = "truertk.pointonenav.com"
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CASTER_PORT = 2101
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MOUNTPOINT = "AUTO"
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USERNAME = "9t7fwfbm57"
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PASSWORD = "96m7bec9g8"
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LAT = 36.1140884
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LON = -97.0880663
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ALT = 390.0
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def build_gga(lat: float, lon: float, alt: float) -> bytes:
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"""Build NMEA GGA sentence."""
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now_utc = datetime.now(timezone.utc).strftime("%H%M%S")
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lat_hemi = "N" if lat >= 0 else "S"
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lat_abs = abs(lat)
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lat_deg = int(lat_abs)
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lat_min = (lat_abs - lat_deg) * 60.0
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lat_str = f"{lat_deg:02d}{lat_min:07.4f}"
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lon_hemi = "E" if lon >= 0 else "W"
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lon_abs = abs(lon)
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lon_deg = int(lon_abs)
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lon_min = (lon_abs - lon_deg) * 60.0
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lon_str = f"{lon_deg:03d}{lon_min:07.4f}"
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fields = ["GPGGA", now_utc, lat_str, lat_hemi, lon_str, lon_hemi, "1", "12", "1.0", f"{alt:.1f}", "M", "", "M", "", ""]
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core = ",".join(fields)
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checksum = 0
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for char in core:
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checksum ^= ord(char)
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return f"${core}*{checksum:02X}\r\n".encode("ascii")
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def make_ntrip_request(host: str, port: int, mount: str, user: str, password: str) -> bytes:
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"""Create NTRIP v2 HTTP request."""
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auth = base64.b64encode(f"{user}:{password}".encode("utf-8")).decode("ascii")
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req = (
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f"GET /{mount} HTTP/1.1\r\n"
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f"Host: {host}:{port}\r\n"
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f"Ntrip-Version: Ntrip/2.0\r\n"
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f"User-Agent: RTCM-208-Decoder/1.0\r\n"
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f"Connection: close\r\n"
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f"Authorization: Basic {auth}\r\n\r\n"
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)
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return req.encode("ascii")
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def decode_message_208(data: bytes, msg_num: int) -> dict:
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"""Decode message 208 and extract fields."""
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result = {
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"message_number": msg_num,
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"timestamp": datetime.now(timezone.utc).isoformat(),
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"length_bytes": len(data),
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"raw_hex": data.hex(),
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}
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# Try decoding as ASCII text
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try:
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text = data.decode('ascii')
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result["text_ascii"] = text
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result["text_repr"] = repr(text)
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except:
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result["text_ascii"] = None
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# Try decoding as UTF-8
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try:
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text_utf8 = data.decode('utf-8')
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result["text_utf8"] = text_utf8
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except:
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result["text_utf8"] = None
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# Check if it looks like comma-separated values
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if result.get("text_ascii"):
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text = result["text_ascii"].strip()
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if "," in text or ";" in text:
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result["appears_csv"] = True
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# Try splitting by common delimiters
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if "," in text:
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parts = text.split(",")
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result["csv_fields"] = parts
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result["csv_field_count"] = len(parts)
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elif ";" in text:
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parts = text.split(";")
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result["csv_fields"] = parts
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result["csv_field_count"] = len(parts)
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# Check if it starts with specific markers
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if len(data) >= 2:
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if data[0:2] == b'\r\n':
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result["starts_with_crlf"] = True
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# Look for printable characters percentage
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printable_count = sum(1 for b in data if 32 <= b < 127 or b in [9, 10, 13])
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result["printable_percent"] = (printable_count / len(data) * 100) if len(data) > 0 else 0
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return result
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def main():
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print(f"RTCM Message 208 Decoder")
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print(f"=" * 80)
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print(f"Caster: {CASTER_HOST}:{CASTER_PORT}/{MOUNTPOINT}")
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print(f"Capturing message 208 for 60 seconds...")
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print(f"=" * 80)
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print()
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messages_208 = []
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last_gga_time = 0
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start_time = time.monotonic()
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total_messages = 0
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msg_208_count = 0
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try:
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# Connect
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print("Connecting...")
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sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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sock.settimeout(30)
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sock.connect((CASTER_HOST, CASTER_PORT))
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sock.sendall(make_ntrip_request(CASTER_HOST, CASTER_PORT, MOUNTPOINT, USERNAME, PASSWORD))
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# Read headers
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header = b""
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while b"\r\n\r\n" not in header:
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chunk = sock.recv(1)
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if not chunk:
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print("ERROR: Connection closed")
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return
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header += chunk
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if "200 OK" not in header.decode("iso-8859-1", errors="replace"):
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print("ERROR: Connection failed")
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return
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print("Connected! Capturing messages...\n")
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# Receive loop
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while time.monotonic() - start_time < 60:
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now = time.monotonic()
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# Send GGA every 10 seconds
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if now - last_gga_time >= 10:
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sock.sendall(build_gga(LAT, LON, ALT))
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elapsed = int(now - start_time)
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print(f"[{elapsed:3d}s] Sent GGA | Total: {total_messages}, Msg 208: {msg_208_count}")
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last_gga_time = now
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# Receive data
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data = sock.recv(4096)
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if not data:
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print("Connection closed")
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break
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# Parse messages
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i = 0
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while i < len(data):
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if data[i] == 0xD3 and i + 2 < len(data):
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length = ((data[i+1] & 0x03) << 8) | data[i+2]
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msg_total_len = 3 + length + 3
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if i + msg_total_len <= len(data) and length >= 3:
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msg_type = (data[i+3] << 4) | (data[i+4] >> 4)
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msg_data = data[i+3:i+3+length]
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total_messages += 1
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if msg_type == 208:
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msg_208_count += 1
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decoded = decode_message_208(msg_data, msg_208_count)
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messages_208.append(decoded)
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# Show first few messages
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if msg_208_count <= 5:
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print(f"\n{'─' * 80}")
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print(f"Message 208 #{msg_208_count} - {length} bytes - {decoded['printable_percent']:.0f}% printable")
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print(f"{'─' * 80}")
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if decoded.get("text_ascii"):
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print(f"ASCII: {decoded['text_repr']}")
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if decoded.get("appears_csv"):
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print(f"CSV Fields ({decoded['csv_field_count']}): {decoded['csv_fields']}")
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else:
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print(f"Hex: {decoded['raw_hex'][:100]}...")
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i += msg_total_len
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continue
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i += 1
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except KeyboardInterrupt:
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print("\n\nInterrupted by user")
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except Exception as e:
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print(f"\nERROR: {e}")
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import traceback
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traceback.print_exc()
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finally:
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if 'sock' in locals():
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try:
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sock.close()
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except:
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pass
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# Analysis
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print(f"\n{'=' * 80}")
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print(f"ANALYSIS")
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print(f"{'=' * 80}")
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print(f"Total messages: {total_messages}")
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print(f"Message 208 captured: {msg_208_count}")
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if messages_208:
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# Check if they're all ASCII
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all_ascii = all(m.get("text_ascii") is not None for m in messages_208)
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print(f"\nAll message 208 are ASCII text: {all_ascii}")
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# Check for CSV pattern
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csv_count = sum(1 for m in messages_208 if m.get("appears_csv"))
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print(f"Messages that appear to be CSV: {csv_count}/{msg_208_count}")
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# Show field count distribution
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if csv_count > 0:
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field_counts = [m.get("csv_field_count", 0) for m in messages_208 if m.get("appears_csv")]
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print(f"CSV field counts: min={min(field_counts)}, max={max(field_counts)}, mode={max(set(field_counts), key=field_counts.count)}")
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# Export to CSV
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csv_filename = "rtcm_208_messages.csv"
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print(f"\nExporting to CSV: {csv_filename}")
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with open(csv_filename, 'w', newline='', encoding='utf-8') as csvfile:
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fieldnames = ["message_number", "timestamp", "length_bytes", "printable_percent",
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"text_ascii", "text_repr", "csv_field_count", "raw_hex"]
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writer = csv.DictWriter(csvfile, fieldnames=fieldnames, extrasaction='ignore')
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writer.writeheader()
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for msg in messages_208:
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writer.writerow(msg)
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print(f"✓ Exported {len(messages_208)} messages to {csv_filename}")
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# If CSV-like, create a parsed CSV
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if csv_count > 0:
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csv_parsed_filename = "rtcm_208_parsed.csv"
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print(f"\nExporting parsed CSV fields: {csv_parsed_filename}")
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# Find max field count
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max_fields = max(m.get("csv_field_count", 0) for m in messages_208 if m.get("appears_csv"))
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with open(csv_parsed_filename, 'w', newline='', encoding='utf-8') as csvfile:
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fieldnames = ["message_number", "timestamp"] + [f"field_{i}" for i in range(max_fields)]
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writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
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writer.writeheader()
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for msg in messages_208:
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if msg.get("appears_csv") and msg.get("csv_fields"):
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row = {
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"message_number": msg["message_number"],
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"timestamp": msg["timestamp"]
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}
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for i, field in enumerate(msg["csv_fields"]):
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row[f"field_{i}"] = field.strip()
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writer.writerow(row)
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print(f"✓ Exported parsed fields to {csv_parsed_filename}")
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# Show sample text from a few messages
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print(f"\n{'=' * 80}")
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print("SAMPLE MESSAGE CONTENT:")
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print(f"{'=' * 80}")
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for i, msg in enumerate(messages_208[:3]):
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print(f"\nMessage #{msg['message_number']}:")
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if msg.get("text_ascii"):
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# Show with visible whitespace
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text = msg["text_ascii"].replace('\r', '\\r').replace('\n', '\\n').replace('\t', '\\t')
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print(f" {text}")
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else:
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print(f" (binary data)")
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if __name__ == "__main__":
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main()
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