// Part of dump1090, a Mode S message decoder for RTLSDR devices. // // track.c: aircraft state tracking // // Copyright (c) 2014,2015 Oliver Jowett // // This file is free software: you may copy, redistribute and/or modify it // under the terms of the GNU General Public License as published by the // Free Software Foundation, either version 2 of the License, or (at your // option) any later version. // // This file is distributed in the hope that it will be useful, but // WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU // General Public License for more details. // // You should have received a copy of the GNU General Public License // along with this program. If not, see . // This file incorporates work covered by the following copyright and // permission notice: // // Copyright (C) 2012 by Salvatore Sanfilippo // // All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // // * Redistributions in binary form must reproduce the above copyright // notice, this list of conditions and the following disclaimer in the // documentation and/or other materials provided with the distribution. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. #include "dump1090.h" // // Return a new aircraft structure for the linked list of tracked // aircraft // struct aircraft *trackCreateAircraft(struct modesMessage *mm) { static struct aircraft zeroAircraft; struct aircraft *a = (struct aircraft *) malloc(sizeof(*a)); int i; // Default everything to zero/NULL *a = zeroAircraft; // Now initialise things that should not be 0/NULL to their defaults a->addr = mm->addr; for (i = 0; i < 8; ++i) a->signalLevel[i] = mm->signalLevel; // First time, initialise everything // to the first signal strength // mm->msgtype 32 is used to represent Mode A/C. These values can never change, so // set them once here during initialisation, and don't bother to set them every // time this ModeA/C is received again in the future if (mm->msgtype == 32) { int modeC = ModeAToModeC(mm->modeA | mm->fs); a->modeACflags = MODEAC_MSG_FLAG; if (modeC < -12) { a->modeACflags |= MODEAC_MSG_MODEA_ONLY; } else { mm->altitude = modeC * 100; mm->bFlags |= MODES_ACFLAGS_ALTITUDE_VALID; } } // Copy the first message so we can emit it later when a second message arrives. a->first_message = *mm; Modes.stats_current.unique_aircraft++; return (a); } // //========================================================================= // // Return the aircraft with the specified address, or NULL if no aircraft // exists with this address. // struct aircraft *trackFindAircraft(uint32_t addr) { struct aircraft *a = Modes.aircrafts; while(a) { if (a->addr == addr) return (a); a = a->next; } return (NULL); } // // CPR position updating // // Distance between points on a spherical earth. // This has up to 0.5% error because the earth isn't actually spherical // (but we don't use it in situations where that matters) static double greatcircle(double lat0, double lon0, double lat1, double lon1) { lat0 = lat0 * M_PI / 180.0; lon0 = lon0 * M_PI / 180.0; lat1 = lat1 * M_PI / 180.0; lon1 = lon1 * M_PI / 180.0; return 6371e3 * acos(sin(lat0) * sin(lat1) + cos(lat0) * cos(lat1) * cos(fabs(lon0 - lon1))); } static int doGlobalCPR(struct aircraft *a, int fflag, int surface) { int result; double lat=0, lon=0; if (surface) { // surface global CPR // find reference location double reflat, reflon; if (a->bFlags & MODES_ACFLAGS_LATLON_REL_OK) { // Ok to try aircraft relative first reflat = a->lat; reflon = a->lon; } else if (Modes.bUserFlags & MODES_USER_LATLON_VALID) { reflat = Modes.fUserLat; reflon = Modes.fUserLon; } else { // No local reference, give up return (-1); } result = decodeCPRsurface(reflat, reflon, a->even_cprlat, a->even_cprlon, a->odd_cprlat, a->odd_cprlon, fflag, &lat, &lon); } else { // airborne global CPR result = decodeCPRairborne(a->even_cprlat, a->even_cprlon, a->odd_cprlat, a->odd_cprlon, fflag, &lat, &lon); } if (result < 0) return result; // check max range if (Modes.maxRange > 0 && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) { double range = greatcircle(Modes.fUserLat, Modes.fUserLon, lat, lon); if (range > Modes.maxRange) return (-2); // we consider an out-of-range value to be bad data } a->lat = lat; a->lon = lon; return 0; } static int doLocalCPR(struct aircraft *a, int fflag, int surface, time_t now) { // relative CPR // find reference location double reflat, reflon, lat=0, lon=0; double range_limit = 0; int result; if (a->bFlags & MODES_ACFLAGS_LATLON_REL_OK) { int elapsed = (int)(now - a->seenLatLon); if (elapsed < 0) elapsed = 0; reflat = a->lat; reflon = a->lon; // impose a range limit based on 2000km/h speed range_limit = 5e3 + (2000e3 * elapsed / 3600); // 5km + 2000km/h } else if (!surface && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) { reflat = Modes.fUserLat; reflon = Modes.fUserLon; // The cell size is at least 360NM, giving a nominal // max range of 180NM (half a cell). // // If the receiver range is more than half a cell // then we must limit this range further to avoid // ambiguity. (e.g. if we receive a position report // at 200NM distance, this may resolve to a position // at (200-360) = 160NM in the wrong direction) if (Modes.maxRange > 1852*180) range_limit = (1852*360) - Modes.maxRange; } else { // No local reference, give up return (-1); } result = decodeCPRrelative(reflat, reflon, fflag ? a->odd_cprlat : a->even_cprlat, fflag ? a->odd_cprlon : a->even_cprlon, fflag, surface, &lat, &lon); if (result < 0) return result; // check range limit if (range_limit > 0) { double range = greatcircle(reflat, reflon, lat, lon); if (range > range_limit) return (-1); } // check max range if (Modes.maxRange > 0 && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) { double range = greatcircle(Modes.fUserLat, Modes.fUserLon, lat, lon); if (range > Modes.maxRange) return (-2); // we consider an out-of-range value to be bad data } a->lat = lat; a->lon = lon; return 0; } static void updatePosition(struct aircraft *a, struct modesMessage *mm, time_t now) { int location_result = -1; int max_elapsed; if (mm->bFlags & MODES_ACFLAGS_AOG) { // Surface: 25 seconds if >25kt or speed unknown, 50 seconds otherwise if ((mm->bFlags & MODES_ACFLAGS_SPEED_VALID) && mm->velocity <= 25) max_elapsed = 50000; else max_elapsed = 25000; } else { // Airborne: 10 seconds max_elapsed = 10000; } if (mm->bFlags & MODES_ACFLAGS_LLODD_VALID) { a->odd_cprlat = mm->raw_latitude; a->odd_cprlon = mm->raw_longitude; a->odd_cprtime = mstime(); } else { a->even_cprlat = mm->raw_latitude; a->even_cprlon = mm->raw_longitude; a->even_cprtime = mstime(); } // If we have enough recent data, try global CPR if (((mm->bFlags | a->bFlags) & MODES_ACFLAGS_LLEITHER_VALID) == MODES_ACFLAGS_LLBOTH_VALID && abs((int)(a->even_cprtime - a->odd_cprtime)) <= max_elapsed) { location_result = doGlobalCPR(a, (mm->bFlags & MODES_ACFLAGS_LLODD_VALID), (mm->bFlags & MODES_ACFLAGS_AOG)); if (location_result == -2) { // Global CPR failed because an airborne position produced implausible results. // This is bad data. Discard both odd and even messages and wait for a fresh pair. // Also disable aircraft-relative positions until we have a new good position (but don't discard the // recorded position itself) Modes.stats_current.cpr_global_bad++; mm->bFlags &= ~(MODES_ACFLAGS_LATLON_VALID | MODES_ACFLAGS_LLODD_VALID | MODES_ACFLAGS_LLEVEN_VALID); a->bFlags &= ~(MODES_ACFLAGS_LATLON_REL_OK | MODES_ACFLAGS_LLODD_VALID | MODES_ACFLAGS_LLEVEN_VALID); return; } else if (location_result == -1) { // No local reference for surface position available, or the two messages crossed a zone. // Nonfatal, try again later. Modes.stats_current.cpr_global_skipped++; } else { Modes.stats_current.cpr_global_ok++; } } // Otherwise try relative CPR. if (location_result == -1) { location_result = doLocalCPR(a, (mm->bFlags & MODES_ACFLAGS_LLODD_VALID), (mm->bFlags & MODES_ACFLAGS_AOG), now); if (location_result == -1) { Modes.stats_current.cpr_local_skipped++; } else { Modes.stats_current.cpr_local_ok++; mm->bFlags |= MODES_ACFLAGS_REL_CPR_USED; } } if (location_result == 0) { // If we sucessfully decoded, back copy the results to mm so that we can print them in list output mm->bFlags |= MODES_ACFLAGS_LATLON_VALID; mm->fLat = a->lat; mm->fLon = a->lon; // Update aircraft state a->bFlags |= (MODES_ACFLAGS_LATLON_VALID | MODES_ACFLAGS_LATLON_REL_OK); a->seenLatLon = a->seen; } } // //========================================================================= // // Receive new messages and update tracked aircraft state // struct aircraft *trackUpdateFromMessage(struct modesMessage *mm) { struct aircraft *a; time_t now = time(NULL); // Lookup our aircraft or create a new one a = trackFindAircraft(mm->addr); if (!a) { // If it's a currently unknown aircraft.... a = trackCreateAircraft(mm); // ., create a new record for it, a->next = Modes.aircrafts; // .. and put it at the head of the list Modes.aircrafts = a; } a->signalLevel[a->messages & 7] = mm->signalLevel;// replace the 8th oldest signal strength a->seen = now; a->messages++; // If a (new) CALLSIGN has been received, copy it to the aircraft structure if (mm->bFlags & MODES_ACFLAGS_CALLSIGN_VALID) { memcpy(a->flight, mm->flight, sizeof(a->flight)); } // If a (new) ALTITUDE has been received, copy it to the aircraft structure if (mm->bFlags & MODES_ACFLAGS_ALTITUDE_VALID) { if ( (a->modeCcount) // if we've a modeCcount already && (a->altitude != mm->altitude ) ) // and Altitude has changed // && (a->modeC != mm->modeC + 1) // and Altitude not changed by +100 feet // && (a->modeC + 1 != mm->modeC ) ) // and Altitude not changes by -100 feet { a->modeCcount = 0; //....zero the hit count a->modeACflags &= ~MODEAC_MSG_MODEC_HIT; } a->altitude = mm->altitude; a->modeC = (mm->altitude + 49) / 100; } // If a (new) SQUAWK has been received, copy it to the aircraft structure if (mm->bFlags & MODES_ACFLAGS_SQUAWK_VALID) { if (a->modeA != mm->modeA) { a->modeAcount = 0; // Squawk has changed, so zero the hit count a->modeACflags &= ~MODEAC_MSG_MODEA_HIT; } a->modeA = mm->modeA; } // If a (new) HEADING has been received, copy it to the aircraft structure if (mm->bFlags & MODES_ACFLAGS_HEADING_VALID) { a->track = mm->heading; } // If a (new) SPEED has been received, copy it to the aircraft structure if (mm->bFlags & MODES_ACFLAGS_SPEED_VALID) { a->speed = mm->velocity; } // If a (new) Vertical Descent rate has been received, copy it to the aircraft structure if (mm->bFlags & MODES_ACFLAGS_VERTRATE_VALID) { a->vert_rate = mm->vert_rate; } // if the Aircraft has landed or taken off since the last message, clear the even/odd CPR flags if ((mm->bFlags & MODES_ACFLAGS_AOG_VALID) && ((a->bFlags ^ mm->bFlags) & MODES_ACFLAGS_AOG)) { a->bFlags &= ~(MODES_ACFLAGS_LLBOTH_VALID | MODES_ACFLAGS_AOG); } // If we've got a new cprlat or cprlon if (mm->bFlags & MODES_ACFLAGS_LLEITHER_VALID) { updatePosition(a, mm, now); } // Update the aircrafts a->bFlags to reflect the newly received mm->bFlags; a->bFlags |= mm->bFlags; if (mm->msgtype == 32) { int flags = a->modeACflags; if ((flags & (MODEAC_MSG_MODEC_HIT | MODEAC_MSG_MODEC_OLD)) == MODEAC_MSG_MODEC_OLD) { // // This Mode-C doesn't currently hit any known Mode-S, but it used to because MODEAC_MSG_MODEC_OLD is // set So the aircraft it used to match has either changed altitude, or gone out of our receiver range // // We've now received this Mode-A/C again, so it must be a new aircraft. It could be another aircraft // at the same Mode-C altitude, or it could be a new airctraft with a new Mods-A squawk. // // To avoid masking this aircraft from the interactive display, clear the MODEAC_MSG_MODES_OLD flag // and set messages to 1; // a->modeACflags = flags & ~MODEAC_MSG_MODEC_OLD; a->messages = 1; } } return (a); } // // Periodic updates of tracking state // // //========================================================================= // // Periodically search through the list of known Mode-S aircraft and tag them if this // Mode A/C matches their known Mode S Squawks or Altitudes(+/- 50feet). // // A Mode S equipped aircraft may also respond to Mode A and Mode C SSR interrogations. // We can't tell if this is a Mode A or C, so scan through the entire aircraft list // looking for matches on Mode A (squawk) and Mode C (altitude). Flag in the Mode S // records that we have had a potential Mode A or Mode C response from this aircraft. // // If an aircraft responds to Mode A then it's highly likely to be responding to mode C // too, and vice verca. Therefore, once the mode S record is tagged with both a Mode A // and a Mode C flag, we can be fairly confident that this Mode A/C frame relates to that // Mode S aircraft. // // Mode C's are more likely to clash than Mode A's; There could be several aircraft // cruising at FL370, but it's less likely (though not impossible) that there are two // aircraft on the same squawk. Therefore, give precidence to Mode A record matches // // Note : It's theoretically possible for an aircraft to have the same value for Mode A // and Mode C. Therefore we have to check BOTH A AND C for EVERY S. // static void trackUpdateAircraftModeA(struct aircraft *a) { struct aircraft *b = Modes.aircrafts; while(b) { if ((b->modeACflags & MODEAC_MSG_FLAG) == 0) { // skip any fudged ICAO records // If both (a) and (b) have valid squawks... if ((a->bFlags & b->bFlags) & MODES_ACFLAGS_SQUAWK_VALID) { // ...check for Mode-A == Mode-S Squawk matches if (a->modeA == b->modeA) { // If a 'real' Mode-S ICAO exists using this Mode-A Squawk b->modeAcount = a->messages; b->modeACflags |= MODEAC_MSG_MODEA_HIT; a->modeACflags |= MODEAC_MSG_MODEA_HIT; if ( (b->modeAcount > 0) && ( (b->modeCcount > 1) || (a->modeACflags & MODEAC_MSG_MODEA_ONLY)) ) // Allow Mode-A only matches if this Mode-A is invalid Mode-C {a->modeACflags |= MODEAC_MSG_MODES_HIT;} // flag this ModeA/C probably belongs to a known Mode S } } // If both (a) and (b) have valid altitudes... if ((a->bFlags & b->bFlags) & MODES_ACFLAGS_ALTITUDE_VALID) { // ... check for Mode-C == Mode-S Altitude matches if ( (a->modeC == b->modeC ) // If a 'real' Mode-S ICAO exists at this Mode-C Altitude || (a->modeC == b->modeC + 1) // or this Mode-C - 100 ft || (a->modeC + 1 == b->modeC ) ) { // or this Mode-C + 100 ft b->modeCcount = a->messages; b->modeACflags |= MODEAC_MSG_MODEC_HIT; a->modeACflags |= MODEAC_MSG_MODEC_HIT; if ( (b->modeAcount > 0) && (b->modeCcount > 1) ) {a->modeACflags |= (MODEAC_MSG_MODES_HIT | MODEAC_MSG_MODEC_OLD);} // flag this ModeA/C probably belongs to a known Mode S } } } b = b->next; } } // //========================================================================= // static void trackUpdateAircraftModeS() { struct aircraft *a = Modes.aircrafts; while(a) { int flags = a->modeACflags; if (flags & MODEAC_MSG_FLAG) { // find any fudged ICAO records // clear the current A,C and S hit bits ready for this attempt a->modeACflags = flags & ~(MODEAC_MSG_MODEA_HIT | MODEAC_MSG_MODEC_HIT | MODEAC_MSG_MODES_HIT); trackUpdateAircraftModeA(a); // and attempt to match them with Mode-S } a = a->next; } } // //========================================================================= // // If we don't receive new nessages within TRACK_AIRCRAFT_TTL // we remove the aircraft from the list. // static void trackRemoveStaleAircraft(time_t now) { struct aircraft *a = Modes.aircrafts; struct aircraft *prev = NULL; while(a) { if ((now - a->seen) > TRACK_AIRCRAFT_TTL || (a->messages == 1 && (now - a->seen) > TRACK_AIRCRAFT_ONEHIT_TTL)) { // Count aircraft where we saw only one message before reaping them. // These are likely to be due to messages with bad addresses. if (a->messages == 1) Modes.stats_current.single_message_aircraft++; // Remove the element from the linked list, with care // if we are removing the first element if (!prev) { Modes.aircrafts = a->next; free(a); a = Modes.aircrafts; } else { prev->next = a->next; free(a); a = prev->next; } } else { prev = a; a = a->next; } } } // // Entry point for periodic updates // void trackPeriodicUpdate() { static time_t next_update; time_t now = time(NULL); // Only do updates once per second if (now >= next_update) { next_update = now; trackRemoveStaleAircraft(now); trackUpdateAircraftModeS(); } }