mirror of
https://github.com/smittix/intercept.git
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Add lat/lon position decode, remove dead parser code
This commit is contained in:
Jim Arndt
+235
-160
@@ -374,6 +374,26 @@ class DSCDecoder:
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109: "PIRACY_ARMED_ROBBERY",
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110: "MAN_OVERBOARD",
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}
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# Telecommand values (Table 11/12), confirmed directly against
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# spec text. This is not the full table - only values we've
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# actually cited are included; anything else reports as
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# UNKNOWN-<code> rather than a guess. 126 ("no information") is
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# by far the most common value for the second telecommand slot,
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# since most calls don't use it for anything.
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TELECOMMAND_TEXT = {
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100: "F3E/G3E ALL MODES TP",
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101: "F3E/G3E DUPLEX TP",
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118: "TEST",
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121: "POSITION_OR_LOCATION_UPDATING",
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126: "NO_INFORMATION",
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}
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# EOS (end of sequence) meaning, per ITU-R M.493 Sec 9, confirmed
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# directly against spec text.
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EOS_TEXT = {
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117: "ACKNOWLEDGEMENT_REQUESTED",
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122: "ACKNOWLEDGEMENT_REPLY",
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127: "NO_ACKNOWLEDGEMENT_REQUIRED",
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}
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VALID_EOS = {117, 122, 127}
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# Field layouts per format specifier: (field_name, symbol_count),
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# in transmission order after the format specifier. Per Table 5
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@@ -513,11 +533,49 @@ class DSCDecoder:
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digits = "".join(f"{s:02d}" for s in syms)
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return digits[:9]
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def decode_position(syms):
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"""
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Decode 5 coordinate symbols into a position dict, per ITU-R
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M.493 Annex 1 Sec 8.1.2/8.2.3 (Table A1-2), confirmed
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consistent across M.493-8 through -15. 10 digits total:
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digit 1 = quadrant (0=NE, 1=NW, 2=SE, 3=SW), digits 2-5 =
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latitude (2 degrees + 2 minutes), digits 6-10 = longitude
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(3 degrees + 2 minutes). All-9s (9999999999) is the spec-
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defined "position not available" sentinel.
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Returns a dict with "lat"/"lon" as signed decimal degrees
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(matching the pre-existing message["position"] shape this
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decoder's downstream consumers - parser.py/routes/dsc.py -
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expect) plus human-readable degree/minute text fields.
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Returns None if the position is unavailable or malformed.
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"""
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if len(syms) != 5 or any(s < 0 or s > 99 for s in syms):
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return None
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digits = "".join(f"{s:02d}" for s in syms)
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if digits == "9999999999":
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return None
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quadrant = int(digits[0])
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lat_deg = int(digits[1:3])
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lat_min = int(digits[3:5])
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lon_deg = int(digits[5:8])
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lon_min = int(digits[8:10])
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lat_sign = 1 if quadrant in (0, 1) else -1 # NE, NW -> North
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lon_sign = 1 if quadrant in (0, 2) else -1 # NE, SE -> East
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lat = lat_sign * (lat_deg + lat_min / 60.0)
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lon = lon_sign * (lon_deg + lon_min / 60.0)
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return {
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"lat": round(lat, 6),
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"lon": round(lon, 6),
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"lat_text": f"{lat_deg:02d}°{lat_min:02d}'{'N' if lat_sign > 0 else 'S'}",
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"lon_text": f"{lon_deg:03d}°{lon_min:02d}'{'E' if lon_sign > 0 else 'W'}",
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}
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message = {
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"type": "dsc",
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"format": format_code,
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"format_text": FORMAT_TEXT.get(format_code, f"UNKNOWN-{format_code}"),
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"eos": eos,
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"eos_text": EOS_TEXT.get(eos, f"UNKNOWN-{eos}"),
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"timestamp": datetime.utcnow().isoformat() + "Z",
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}
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if is_distress_ack:
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@@ -545,10 +603,49 @@ class DSCDecoder:
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message["nature_text"] = NATURE_TEXT.get(nature_val, f"UNKNOWN-{nature_val}")
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if "coordinates" in fields:
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message["coordinates_raw"] = fields["coordinates"]
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message["position"] = decode_position(fields["coordinates"])
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if "time" in fields:
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message["time_raw"] = fields["time"]
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if "telecommand" in fields:
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message["telecommand"] = fields["telecommand"]
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message["telecommand_text"] = [
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TELECOMMAND_TEXT.get(t, f"UNKNOWN-{t}") for t in fields["telecommand"]
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]
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# Plain-English summary, built from the fields actually present -
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# different message types (individual/group/area, all ships,
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# distress alert, distress ack/self-cancel) have different fields,
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# so this is assembled per-type rather than one fixed template.
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eos_phrase = {
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117: "requesting acknowledgement",
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122: "acknowledging a previous call",
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127: "no acknowledgement required",
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}.get(eos, "unknown EOS")
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tc_phrase = message.get("telecommand_text", [None])[0]
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tc_phrase = f", purpose: {tc_phrase}" if tc_phrase and tc_phrase != "NO_INFORMATION" else ""
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if is_distress_ack:
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message["summary"] = (
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f"Distress self-cancel/acknowledgement from {message.get('source_mmsi')} "
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f"for vessel {message.get('ship_in_distress_mmsi')} "
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f"(original distress nature: {message.get('nature_text', 'unknown')})"
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)
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elif format_code == 112:
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message["summary"] = (
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f"DISTRESS ALERT from {message.get('source_mmsi')} - "
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f"nature: {message.get('nature_text', 'unknown')}"
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)
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elif "dest_mmsi" in message:
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message["summary"] = (
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f"{message.get('category', 'UNKNOWN')} individual/group call from "
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f"{message.get('source_mmsi')} to {message.get('dest_mmsi')}, "
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f"{eos_phrase}{tc_phrase}"
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)
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else:
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message["summary"] = (
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f"{message.get('category', 'UNKNOWN')} broadcast from "
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f"{message.get('source_mmsi')} to all ships, {eos_phrase}{tc_phrase}"
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)
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return message
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@@ -621,6 +718,144 @@ class DSCDecoder:
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return (f"format={format_code}, all fields complete, but no valid EOS "
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f"found in remaining {len(dedup) - idx} symbols")
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def _diagnose_decode_failure(self) -> str:
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"""
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Explain exactly why the current message_bits buffer failed to
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decode, for logging at timeout. Mirrors _try_decode_message's
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logic but reports where it stopped instead of returning None
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silently - normal accumulation still returns None quietly (this
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is only called once, at the moment of timeout, not on every
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partial-accumulation call).
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"""
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FORMAT_SPECIFIERS = {102, 112, 114, 116, 120, 123}
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FIELD_LAYOUTS = {
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120: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3), ("frequency_2", 3)],
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123: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3)],
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116: [("category", 1), ("self_id", 5), ("telecommand", 2),
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("frequency_1", 3)],
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114: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3), ("frequency_2", 3)],
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102: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3), ("frequency_2", 3)],
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112: [("self_id", 5), ("nature", 1), ("coordinates", 5),
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("time", 2), ("telecommand_msg4", 1)],
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}
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VALID_EOS = {117, 122, 127}
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num_symbols = len(self.message_bits) // 10
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symbols = [self._bits_to_symbol(self.message_bits[i * 10:i * 10 + 10]) for i in range(num_symbols)]
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invalid_count = sum(1 for s in symbols if s == -1)
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anchor = None
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for i in range(len(symbols) - 2):
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if symbols[i] in FORMAT_SPECIFIERS and symbols[i] == symbols[i + 2]:
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anchor = i
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break
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if anchor is None:
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return (f"no anchor found ({num_symbols} symbols, {invalid_count} invalid, "
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f"first 15 symbols={symbols[:15]})")
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dedup = symbols[anchor::2]
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dedup_b = symbols[anchor + 1::2]
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def value_at(k):
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primary = dedup[k] if k < len(dedup) else -1
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if primary != -1:
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return primary
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fb = k + 2
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return dedup_b[fb] if 0 <= fb < len(dedup_b) else -1
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format_code = value_at(0)
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layout = FIELD_LAYOUTS.get(format_code)
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if layout is None:
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return f"anchor found at {anchor}, but format specifier {format_code} not recognized"
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idx = 2
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for name, count in layout:
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if idx + count > len(dedup):
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have = len(dedup) - idx
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return (f"format={format_code}, stalled waiting for field "
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f"'{name}' (need {count} symbols, have {max(have, 0)})")
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idx += count
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for k in range(idx, len(dedup)):
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if value_at(k) in VALID_EOS:
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return "all fields complete, EOS found - should have decoded (unexpected)"
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return (f"format={format_code}, all fields complete, but no valid EOS "
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f"found in remaining {len(dedup) - idx} symbols")
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def _diagnose_decode_failure(self) -> str:
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"""
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Explain exactly why the current message_bits buffer failed to
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decode, for logging at timeout. Mirrors _try_decode_message's
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logic but reports where it stopped instead of returning None
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silently - normal accumulation still returns None quietly (this
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is only called once, at the moment of timeout, not on every
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partial-accumulation call).
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"""
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FORMAT_SPECIFIERS = {102, 112, 114, 116, 120, 123}
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FIELD_LAYOUTS = {
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120: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3), ("frequency_2", 3)],
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123: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3)],
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116: [("category", 1), ("self_id", 5), ("telecommand", 2),
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("frequency_1", 3)],
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114: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3), ("frequency_2", 3)],
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102: [("address", 5), ("category", 1), ("self_id", 5),
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("telecommand", 2), ("frequency_1", 3), ("frequency_2", 3)],
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112: [("self_id", 5), ("nature", 1), ("coordinates", 5),
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("time", 2), ("telecommand_msg4", 1)],
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}
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VALID_EOS = {117, 122, 127}
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num_symbols = len(self.message_bits) // 10
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symbols = [self._bits_to_symbol(self.message_bits[i * 10:i * 10 + 10]) for i in range(num_symbols)]
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invalid_count = sum(1 for s in symbols if s == -1)
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anchor = None
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for i in range(len(symbols) - 2):
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if symbols[i] in FORMAT_SPECIFIERS and symbols[i] == symbols[i + 2]:
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anchor = i
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break
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if anchor is None:
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return (f"no anchor found ({num_symbols} symbols, {invalid_count} invalid, "
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f"first 15 symbols={symbols[:15]})")
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dedup = symbols[anchor::2]
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dedup_b = symbols[anchor + 1::2]
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def value_at(k):
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primary = dedup[k] if k < len(dedup) else -1
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if primary != -1:
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return primary
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fb = k + 2
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return dedup_b[fb] if 0 <= fb < len(dedup_b) else -1
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format_code = value_at(0)
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layout = FIELD_LAYOUTS.get(format_code)
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if layout is None:
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return f"anchor found at {anchor}, but format specifier {format_code} not recognized"
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idx = 2
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for name, count in layout:
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if idx + count > len(dedup):
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have = len(dedup) - idx
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return (f"format={format_code}, stalled waiting for field "
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f"'{name}' (need {count} symbols, have {max(have, 0)})")
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idx += count
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for k in range(idx, len(dedup)):
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if value_at(k) in VALID_EOS:
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return "all fields complete, EOS found - should have decoded (unexpected)"
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return (f"format={format_code}, all fields complete, but no valid EOS "
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f"found in remaining {len(dedup) - idx} symbols")
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def _bits_to_symbol(self, bits: list[int]) -> int:
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"""
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Convert 10 bits to symbol value.
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@@ -659,166 +894,6 @@ class DSCDecoder:
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return value
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def _decode_symbols(self, symbols: list[int]) -> dict | None:
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"""
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Decode DSC symbol sequence to message.
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Message structure (symbols):
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0: Format specifier
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1-5: Address/MMSI (encoded)
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6-10: Self-ID/MMSI (encoded)
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11+: Variable fields depending on format
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Last: EOS (127)
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Args:
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symbols: List of decoded symbol values
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Returns:
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Decoded message dict or None if invalid
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"""
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if len(symbols) < 12:
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return None
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try:
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# Format specifier (first non-phasing symbol)
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format_code = symbols[0]
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format_text = FORMAT_CODES.get(format_code, f"UNKNOWN-{format_code}")
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# Derive category from format specifier per ITU-R M.493
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if format_code == 120:
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category = "DISTRESS"
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elif format_code == 123:
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category = "ALL_SHIPS_URGENCY_SAFETY"
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elif format_code == 102:
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category = "ALL_SHIPS"
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elif format_code == 116:
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category = "GROUP"
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elif format_code == 112:
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category = "INDIVIDUAL"
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elif format_code == 114:
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category = "INDIVIDUAL_ACK"
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else:
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category = FORMAT_CODES.get(format_code, "UNKNOWN")
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# Decode MMSI from symbols 1-5 (destination/address)
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dest_mmsi = self._decode_mmsi(symbols[1:6])
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if dest_mmsi is None:
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return None
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# Decode self-ID from symbols 6-10 (source)
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source_mmsi = self._decode_mmsi(symbols[6:11])
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if source_mmsi is None:
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return None
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message = {
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"type": "dsc",
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"format": format_code,
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"format_text": format_text,
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"category": category,
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"source_mmsi": source_mmsi,
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"dest_mmsi": dest_mmsi,
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"timestamp": datetime.utcnow().isoformat() + "Z",
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}
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# Parse additional fields based on format
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remaining = symbols[11:-1] # Exclude EOS
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if category in ("DISTRESS", "DISTRESS_RELAY"):
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# Distress messages have nature and position
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if len(remaining) >= 1:
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message["nature"] = remaining[0]
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message["nature_text"] = DISTRESS_NATURE_CODES.get(remaining[0], f"UNKNOWN-{remaining[0]}")
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# Try to decode position
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if len(remaining) >= 11:
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position = self._decode_position(remaining[1:11])
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if position:
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message["position"] = position
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# Telecommand fields (last two before EOS) — only for formats
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# that carry telecommand fields per ITU-R M.493
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if format_code in TELECOMMAND_FORMATS and len(remaining) >= 2:
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message["telecommand1"] = remaining[-2]
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message["telecommand2"] = remaining[-1]
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# Add raw data for debugging
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message["raw"] = "".join(f"{s:03d}" for s in symbols)
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logger.info(f"Decoded DSC: {category} from {source_mmsi}")
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return message
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except Exception as e:
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logger.warning(f"DSC decode error: {e}")
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return None
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def _decode_mmsi(self, symbols: list[int]) -> str | None:
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"""
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Decode MMSI from 5 DSC symbols.
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Each symbol represents 2 BCD digits (00-99).
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5 symbols = 10 digits, but MMSI is 9 digits (first symbol has leading 0).
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Returns None if any symbol is out of valid BCD range.
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"""
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if len(symbols) < 5:
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return None
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digits = []
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for sym in symbols:
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if sym < 0 or sym > 99:
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return None
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# Each symbol is 2 BCD digits
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digits.append(f"{sym:02d}")
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mmsi = "".join(digits)
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# MMSI is 9 digits - trim the leading digit from the 10-digit
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# BCD result since the first symbol's high digit is always 0
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if len(mmsi) > 9:
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mmsi = mmsi[1:]
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return mmsi.zfill(9)
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def _decode_position(self, symbols: list[int]) -> dict | None:
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"""
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Decode position from 10 DSC symbols.
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Position encoding (ITU-R M.493):
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- Quadrant (10=NE, 11=NW, 00=SE, 01=SW)
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- Latitude degrees (2 digits)
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- Latitude minutes (2 digits)
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- Longitude degrees (3 digits)
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- Longitude minutes (2 digits)
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"""
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if len(symbols) < 10:
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return None
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try:
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# Quadrant indicator
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quadrant = symbols[0]
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lat_sign = 1 if quadrant in (10, 11) else -1
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lon_sign = 1 if quadrant in (10, 0) else -1
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# Latitude degrees and minutes
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lat_deg = symbols[1] if symbols[1] <= 90 else 0
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lat_min = symbols[2] if symbols[2] < 60 else 0
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# Longitude degrees (3 digits from 2 symbols)
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lon_deg_high = symbols[3] if symbols[3] < 10 else 0
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lon_deg_low = symbols[4] if symbols[4] < 100 else 0
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lon_deg = lon_deg_high * 100 + lon_deg_low
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if lon_deg > 180:
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lon_deg = 0
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||||
lon_min = symbols[5] if symbols[5] < 60 else 0
|
||||
|
||||
lat = lat_sign * (lat_deg + lat_min / 60.0)
|
||||
lon = lon_sign * (lon_deg + lon_min / 60.0)
|
||||
|
||||
return {"lat": round(lat, 6), "lon": round(lon, 6)}
|
||||
|
||||
except Exception:
|
||||
return None
|
||||
|
||||
|
||||
def read_audio_stdin() -> Generator[bytes, None, None]:
|
||||
"""
|
||||
Read audio from stdin in chunks.
|
||||
|
||||
Reference in New Issue
Block a user