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brentperteet
254
rtcm_208_analyzer.py
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254
rtcm_208_analyzer.py
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#!/usr/bin/env python3
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"""
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Analyzer for RTCM message 208 (proprietary).
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Captures message 208 and displays hex dump with field analysis.
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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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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 = "POLARIS_LOCAL"
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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-Analyzer/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 hex_dump(data: bytes, offset: int = 0, width: int = 16) -> str:
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"""Create a hex dump with ASCII representation."""
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lines = []
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for i in range(0, len(data), width):
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chunk = data[i:i+width]
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hex_part = " ".join(f"{b:02X}" for b in chunk)
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ascii_part = "".join(chr(b) if 32 <= b < 127 else "." for b in chunk)
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lines.append(f"{offset + i:04X} {hex_part:<{width*3}} {ascii_part}")
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return "\n".join(lines)
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def analyze_message_208(data: bytes, msg_num: int):
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"""Analyze and display structure of message 208."""
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print(f"\n{'=' * 80}")
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print(f"MESSAGE 208 #{msg_num} - Length: {len(data)} bytes")
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print(f"{'=' * 80}")
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# Show hex dump
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print("\nHex Dump:")
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print(hex_dump(data))
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# Try to extract some common fields
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print(f"\n{'─' * 80}")
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print("Field Analysis:")
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print(f"{'─' * 80}")
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if len(data) >= 3:
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# Message type (12 bits)
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msg_type = (data[0] << 4) | (data[1] >> 4)
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print(f"Message Type: {msg_type}")
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# Station/Reference ID (typically next 12 bits)
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if len(data) >= 3:
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ref_id = ((data[1] & 0x0F) << 8) | data[2]
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print(f"Reference/Station ID: {ref_id}")
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# Show first 20 bytes as decimal
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print(f"\nFirst bytes (decimal): {[data[i] for i in range(min(20, len(data)))]}")
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# Try to find patterns
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print(f"\n{'─' * 80}")
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print("Attempting pattern recognition:")
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print(f"{'─' * 80}")
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# Look for typical RTCM structures
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if len(data) >= 10:
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# Check for possible timestamp (GPS TOW in ms)
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possible_time_1 = (data[3] << 22) | (data[4] << 14) | (data[5] << 6) | (data[6] >> 2)
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print(f"Possible GPS TOW (ms) at byte 3: {possible_time_1} ({possible_time_1/1000:.1f} sec)")
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# Check for possible coordinates or large numbers
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for i in range(3, min(len(data) - 4, 10)):
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val32 = (data[i] << 24) | (data[i+1] << 16) | (data[i+2] << 8) | data[i+3]
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if val32 != 0:
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val32_signed = val32 if val32 < 0x80000000 else val32 - 0x100000000
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print(f"32-bit value at byte {i}: {val32} (signed: {val32_signed})")
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def main():
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print(f"RTCM Message 208 Analyzer")
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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"Will capture first 10 instances of message 208")
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print(f"=" * 80)
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print()
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msg_208_samples = []
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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! Searching for message 208...\n")
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# Receive loop
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while msg_208_count < 10:
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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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print(f"[{int(now - start_time):3d}s] Sent GGA | Total msgs: {total_messages}, Msg 208 found: {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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msg_208_samples.append(msg_data)
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print(f"✓ Found message 208 #{msg_208_count} (length: {length} bytes)")
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if msg_208_count <= 3: # Show first 3 immediately
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analyze_message_208(msg_data, msg_208_count)
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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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# Final summary
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print(f"\n{'=' * 80}")
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print(f"SUMMARY")
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print(f"{'=' * 80}")
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print(f"Total messages received: {total_messages}")
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print(f"Message 208 instances: {msg_208_count}")
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if msg_208_samples:
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# Show statistics
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lengths = [len(m) for m in msg_208_samples]
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print(f"\nMessage 208 length statistics:")
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print(f" Min: {min(lengths)} bytes")
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print(f" Max: {max(lengths)} bytes")
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print(f" Most common: {max(set(lengths), key=lengths.count)} bytes ({lengths.count(max(set(lengths), key=lengths.count))} instances)")
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# Compare first few messages to find common/changing fields
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if len(msg_208_samples) >= 2:
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print(f"\n{'─' * 80}")
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print("Comparing first 2 messages to identify static vs. dynamic fields:")
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print(f"{'─' * 80}")
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msg1 = msg_208_samples[0]
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msg2 = msg_208_samples[1]
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min_len = min(len(msg1), len(msg2))
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static_bytes = []
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dynamic_bytes = []
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for i in range(min_len):
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if msg1[i] == msg2[i]:
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static_bytes.append(i)
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else:
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dynamic_bytes.append(i)
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print(f"Static byte positions: {static_bytes[:20]}{'...' if len(static_bytes) > 20 else ''}")
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print(f"Dynamic byte positions: {dynamic_bytes[:20]}{'...' if len(dynamic_bytes) > 20 else ''}")
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print(f"\nByte-by-byte comparison (first 30 bytes):")
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print("Byte# Msg1 Msg2 Same")
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print("─" * 30)
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for i in range(min(30, min_len)):
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same = "✓" if msg1[i] == msg2[i] else "✗"
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print(f"{i:4d} {msg1[i]:02X} {msg2[i]:02X} {same}")
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if __name__ == "__main__":
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main()
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