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brentperteet
190
rtcm_208_capture.py
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190
rtcm_208_capture.py
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#!/usr/bin/env python3
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"""
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Capture raw RTCM message 208 to binary file for manual 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
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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.utcnow().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-Capture/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 main():
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timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
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output_file = f"rtcm_208_raw_{timestamp}.bin"
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index_file = f"rtcm_208_index_{timestamp}.txt"
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print(f"RTCM Message 208 Raw Capture")
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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"Output: {output_file}")
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print(f"Index: {index_file}")
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print(f"Capturing for 60 seconds or 20 messages, whichever comes first...")
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print(f"=" * 80)
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print()
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last_gga_time = 0
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start_time = time.monotonic()
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msg_208_count = 0
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total_messages = 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!\n")
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# Open output files
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with open(output_file, 'wb') as binfile, open(index_file, 'w') as idxfile:
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idxfile.write(f"# RTCM 208 Message Index\n")
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idxfile.write(f"# Captured: {datetime.now().isoformat()}\n")
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idxfile.write(f"# Format: message_number, offset, length, timestamp\n")
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idxfile.write(f"#\n")
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file_offset = 0
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# Receive loop
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while time.monotonic() - start_time < 60 and msg_208_count < 20:
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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] Total: {total_messages}, Msg 208: {msg_208_count}/20")
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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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total_messages += 1
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if msg_type == 208:
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msg_208_count += 1
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msg_data = data[i+3:i+3+length] # Just the payload
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# Write to binary file
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binfile.write(msg_data)
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binfile.flush()
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# Write to index
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ts = datetime.now().isoformat()
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idxfile.write(f"{msg_208_count},{file_offset},{length},{ts}\n")
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idxfile.flush()
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print(f" ✓ Captured message 208 #{msg_208_count} - {length} bytes at offset {file_offset}")
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file_offset += length
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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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print(f"\n{'=' * 80}")
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print(f"CAPTURE COMPLETE")
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print(f"{'=' * 80}")
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print(f"Messages captured: {msg_208_count}")
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print(f"Output file: {output_file} ({file_offset} bytes)")
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print(f"Index file: {index_file}")
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print()
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print("To view the binary file:")
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print(f" hexdump -C {output_file}")
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print(f" xxd {output_file}")
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print()
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print("To extract a specific message (e.g., message #1):")
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print(" 1. Look up offset and length in index file")
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print(" 2. Use: dd if={output_file} bs=1 skip=<offset> count=<length> | hexdump -C")
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if __name__ == "__main__":
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main()
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