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// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// track.c: aircraft state tracking
//
// Copyright (c) 2014-2016 Oliver Jowett <oliver@mutability.co.uk>
//
// 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 <http://www.gnu.org/licenses/>.
// This file incorporates work covered by the following copyright and
// permission notice:
//
// Copyright (C) 2012 by Salvatore Sanfilippo <antirez@gmail.com>
//
// 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"
#include <inttypes.h>
/* #define DEBUG_CPR_CHECKS */
//
// 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;
a->addrtype = mm->addrtype;
for (i = 0; i < 8; ++i)
a->signalLevel[i] = 1e-5;
a->signalNext = 0;
// start off with the "last emitted" ACAS RA being blank (just the BDS 3,0 code)
a->fatsv_emitted_bds_30[0] = 0x30;
// 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) {
a->modeACflags = MODEAC_MSG_FLAG;
if (!mm->altitude_valid) {
a->modeACflags |= MODEAC_MSG_MODEA_ONLY;
}
}
// 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);
}
// Should we accept some new data from the given source?
// If so, update the validity and return 1
static int accept_data(data_validity *d, datasource_t source, uint64_t now)
{
if (source < d->source && now < d->stale)
return 0;
d->source = source;
d->updated = now;
d->stale = now + 60000;
d->expires = now + 70000;
return 1;
}
// Given two datasources, produce a third datasource for data combined from them.
static void combine_validity(data_validity *to, const data_validity *from1, const data_validity *from2) {
if (from1->source == SOURCE_INVALID) {
*to = *from2;
return;
}
if (from2->source == SOURCE_INVALID) {
*to = *from1;
return;
}
to->source = (from1->source < from2->source) ? from1->source : from2->source; // the worse of the two input sources
to->updated = (from1->updated > from2->updated) ? from1->updated : from2->updated; // the *later* of the two update times
to->stale = (from1->stale < from2->stale) ? from1->stale : from2->stale; // the earlier of the two stale times
to->expires = (from1->expires < from2->expires) ? from1->expires : from2->expires; // the earlier of the two expiry times
}
static int compare_validity(const data_validity *lhs, const data_validity *rhs, uint64_t now) {
if (now < lhs->stale && lhs->source > rhs->source)
return 1;
else if (now < rhs->stale && lhs->source < rhs->source)
return -1;
else if (lhs->updated > rhs->updated)
return 1;
else if (lhs->updated < rhs->updated)
return -1;
else
return 0;
}
//
// 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)
{
double dlat, dlon;
lat0 = lat0 * M_PI / 180.0;
lon0 = lon0 * M_PI / 180.0;
lat1 = lat1 * M_PI / 180.0;
lon1 = lon1 * M_PI / 180.0;
dlat = fabs(lat1 - lat0);
dlon = fabs(lon1 - lon0);
// use haversine for small distances for better numerical stability
if (dlat < 0.001 && dlon < 0.001) {
double a = sin(dlat/2) * sin(dlat/2) + cos(lat0) * cos(lat1) * sin(dlon/2) * sin(dlon/2);
return 6371e3 * 2 * atan2(sqrt(a), sqrt(1.0 - a));
}
// spherical law of cosines
return 6371e3 * acos(sin(lat0) * sin(lat1) + cos(lat0) * cos(lat1) * cos(dlon));
}
static void update_range_histogram(double lat, double lon)
{
if (Modes.stats_range_histo && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) {
double range = greatcircle(Modes.fUserLat, Modes.fUserLon, lat, lon);
int bucket = round(range / Modes.maxRange * RANGE_BUCKET_COUNT);
if (bucket < 0)
bucket = 0;
else if (bucket >= RANGE_BUCKET_COUNT)
bucket = RANGE_BUCKET_COUNT-1;
++Modes.stats_current.range_histogram[bucket];
}
}
// return true if it's OK for the aircraft to have travelled from its last known position
// to a new position at (lat,lon,surface) at a time of now.
static int speed_check(struct aircraft *a, double lat, double lon, uint64_t now, int surface)
{
uint64_t elapsed;
double distance;
double range;
int speed;
int inrange;
if (!trackDataValid(&a->position_valid))
return 1; // no reference, assume OK
elapsed = trackDataAge(&a->position_valid, now);
if (trackDataValid(&a->speed_valid))
speed = a->speed;
else if (trackDataValid(&a->speed_ias_valid))
speed = a->speed_ias * 4 / 3;
else if (trackDataValid(&a->speed_tas_valid))
speed = a->speed_tas * 4 / 3;
else
speed = surface ? 100 : 600; // guess
// Work out a reasonable speed to use:
// current speed + 1/3
// surface speed min 20kt, max 150kt
// airborne speed min 200kt, no max
speed = speed * 4 / 3;
if (surface) {
if (speed < 20)
speed = 20;
if (speed > 150)
speed = 150;
} else {
if (speed < 200)
speed = 200;
}
// 100m (surface) or 500m (airborne) base distance to allow for minor errors,
// plus distance covered at the given speed for the elapsed time + 1 second.
range = (surface ? 0.1e3 : 0.5e3) + ((elapsed + 1000.0) / 1000.0) * (speed * 1852.0 / 3600.0);
// find actual distance
distance = greatcircle(a->lat, a->lon, lat, lon);
inrange = (distance <= range);
#ifdef DEBUG_CPR_CHECKS
if (!inrange) {
fprintf(stderr, "Speed check failed: %06x: %.3f,%.3f -> %.3f,%.3f in %.1f seconds, max speed %d kt, range %.1fkm, actual %.1fkm\n",
a->addr, a->lat, a->lon, lat, lon, elapsed/1000.0, speed, range/1000.0, distance/1000.0);
}
#endif
return inrange;
}
static int doGlobalCPR(struct aircraft *a, struct modesMessage *mm, uint64_t now, double *lat, double *lon, unsigned *nuc)
{
int result;
int fflag = mm->cpr_odd;
int surface = (mm->airground == AG_GROUND);
*nuc = (a->cpr_even_nuc < a->cpr_odd_nuc ? a->cpr_even_nuc : a->cpr_odd_nuc); // worst of the two positions
if (surface) {
// surface global CPR
// find reference location
double reflat, reflon;
if (trackDataValidEx(&a->position_valid, now, 50000, SOURCE_INVALID)) { // Ok to try aircraft relative first
reflat = a->lat;
reflon = a->lon;
if (a->pos_nuc < *nuc)
*nuc = a->pos_nuc;
} 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->cpr_even_lat, a->cpr_even_lon,
a->cpr_odd_lat, a->cpr_odd_lon,
fflag,
lat, lon);
} else {
// airborne global CPR
result = decodeCPRairborne(a->cpr_even_lat, a->cpr_even_lon,
a->cpr_odd_lat, a->cpr_odd_lon,
fflag,
lat, lon);
}
if (result < 0) {
#ifdef DEBUG_CPR_CHECKS
fprintf(stderr, "CPR: decode failure for %06X (%d).\n", a->addr, result);
fprintf(stderr, " even: %d %d odd: %d %d fflag: %s\n",
a->cpr_even_lat, a->cpr_even_lon,
a->cpr_odd_lat, a->cpr_odd_lon,
fflag ? "odd" : "even");
#endif
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) {
#ifdef DEBUG_CPR_CHECKS
fprintf(stderr, "Global range check failed: %06x: %.3f,%.3f, max range %.1fkm, actual %.1fkm\n",
a->addr, *lat, *lon, Modes.maxRange/1000.0, range/1000.0);
#endif
Modes.stats_current.cpr_global_range_checks++;
return (-2); // we consider an out-of-range value to be bad data
}
}
// for mlat results, skip the speed check
if (mm->source == SOURCE_MLAT)
return result;
// check speed limit
if (trackDataValid(&a->position_valid) && a->pos_nuc >= *nuc && !speed_check(a, *lat, *lon, now, surface)) {
Modes.stats_current.cpr_global_speed_checks++;
return -2;
}
return result;
}
static int doLocalCPR(struct aircraft *a, struct modesMessage *mm, uint64_t now, double *lat, double *lon, unsigned *nuc)
{
// relative CPR
// find reference location
double reflat, reflon;
double range_limit = 0;
int result;
int fflag = mm->cpr_odd;
int surface = (mm->airground == AG_GROUND);
*nuc = mm->cpr_nucp;
if (trackDataValidEx(&a->position_valid, now, 50000, SOURCE_INVALID)) {
reflat = a->lat;
reflon = a->lon;
if (a->pos_nuc < *nuc)
*nuc = a->pos_nuc;
range_limit = 50e3;
} 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 == 0) {
return (-1); // Can't do receiver-centered checks at all
} else if (Modes.maxRange <= 1852*180) {
range_limit = Modes.maxRange;
} else if (Modes.maxRange < 1852*360) {
range_limit = (1852*360) - Modes.maxRange;
} else {
return (-1); // Can't do receiver-centered checks at all
}
} else {
// No local reference, give up
return (-1);
}
result = decodeCPRrelative(reflat, reflon,
mm->cpr_lat,
mm->cpr_lon,
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) {
Modes.stats_current.cpr_local_range_checks++;
return (-1);
}
}
// check speed limit
if (trackDataValid(&a->position_valid) && a->pos_nuc >= *nuc && !speed_check(a, *lat, *lon, now, surface)) {
#ifdef DEBUG_CPR_CHECKS
fprintf(stderr, "Speed check for %06X with local decoding failed\n", a->addr);
#endif
Modes.stats_current.cpr_local_speed_checks++;
return -1;
}
return 0;
}
static uint64_t time_between(uint64_t t1, uint64_t t2)
{
if (t1 >= t2)
return t1 - t2;
else
return t2 - t1;
}
static void updatePosition(struct aircraft *a, struct modesMessage *mm, uint64_t now)
{
int location_result = -1;
uint64_t max_elapsed;
double new_lat = 0, new_lon = 0;
unsigned new_nuc = 0;
int surface;
surface = (mm->airground == AG_GROUND);
if (surface) {
++Modes.stats_current.cpr_surface;
// Surface: 25 seconds if >25kt or speed unknown, 50 seconds otherwise
if (mm->speed_valid && mm->speed <= 25)
max_elapsed = 50000;
else
max_elapsed = 25000;
} else {
++Modes.stats_current.cpr_airborne;
// Airborne: 10 seconds
max_elapsed = 10000;
}
// If we have enough recent data, try global CPR
if (trackDataValid(&a->cpr_odd_valid) && trackDataValid(&a->cpr_even_valid) &&
a->cpr_odd_valid.source == a->cpr_even_valid.source &&
a->cpr_odd_airground == a->cpr_even_airground &&
time_between(a->cpr_odd_valid.updated, a->cpr_even_valid.updated) <= max_elapsed) {
location_result = doGlobalCPR(a, mm, now, &new_lat, &new_lon, &new_nuc);
if (location_result == -2) {
#ifdef DEBUG_CPR_CHECKS
fprintf(stderr, "global CPR failure (invalid) for (%06X).\n", a->addr);
#endif
// Global CPR failed because the 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++;
a->cpr_odd_valid.source = a->cpr_even_valid.source = a->position_valid.source = SOURCE_INVALID;
return;
} else if (location_result == -1) {
#ifdef DEBUG_CPR_CHECKS
if (mm->source == SOURCE_MLAT) {
fprintf(stderr, "CPR skipped from MLAT (%06X).\n", a->addr);
}
#endif
// 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++;
combine_validity(&a->position_valid, &a->cpr_even_valid, &a->cpr_odd_valid);
}
}
// Otherwise try relative CPR.
if (location_result == -1) {
location_result = doLocalCPR(a, mm, now, &new_lat, &new_lon, &new_nuc);
if (location_result < 0) {
Modes.stats_current.cpr_local_skipped++;
} else {
Modes.stats_current.cpr_local_ok++;
mm->cpr_relative = 1;
if (mm->cpr_odd) {
a->position_valid = a->cpr_odd_valid;
} else {
a->position_valid = a->cpr_even_valid;
}
}
}
if (location_result == 0) {
// If we sucessfully decoded, back copy the results to mm so that we can print them in list output
mm->cpr_decoded = 1;
mm->decoded_lat = new_lat;
mm->decoded_lon = new_lon;
// Update aircraft state
a->lat = new_lat;
a->lon = new_lon;
a->pos_nuc = new_nuc;
update_range_histogram(new_lat, new_lon);
}
}
//
//=========================================================================
//
// Receive new messages and update tracked aircraft state
//
struct aircraft *trackUpdateFromMessage(struct modesMessage *mm)
{
struct aircraft *a;
uint64_t now = mstime();
// 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;
}
if (mm->signalLevel > 0) {
a->signalLevel[a->signalNext] = mm->signalLevel;
a->signalNext = (a->signalNext + 1) & 7;
}
a->seen = now;
a->messages++;
// update addrtype, we only ever go towards "more direct" types
if (mm->addrtype < a->addrtype)
a->addrtype = mm->addrtype;
if (mm->altitude_valid && mm->altitude_source == ALTITUDE_BARO && accept_data(&a->altitude_valid, mm->source, now)) {
unsigned modeC = (a->altitude + 49) / 100;
if (modeC != a->altitude_modeC) {
a->modeCcount = 0; //....zero the hit count
a->modeACflags &= ~MODEAC_MSG_MODEC_HIT;
}
a->altitude = mm->altitude;
a->altitude_modeC = modeC;
}
if (mm->squawk_valid && accept_data(&a->squawk_valid, mm->source, now)) {
if (mm->squawk != a->squawk) {
a->modeAcount = 0; //....zero the hit count
a->modeACflags &= ~MODEAC_MSG_MODEA_HIT;
}
a->squawk = mm->squawk;
}
if (mm->altitude_valid && mm->altitude_source == ALTITUDE_GNSS && accept_data(&a->altitude_gnss_valid, mm->source, now)) {
a->altitude_gnss = mm->altitude;
}
if (mm->gnss_delta_valid && accept_data(&a->gnss_delta_valid, mm->source, now)) {
a->gnss_delta = mm->gnss_delta;
}
if (mm->heading_valid && mm->heading_source == HEADING_TRUE && accept_data(&a->heading_valid, mm->source, now)) {
a->heading = mm->heading;
}
if (mm->heading_valid && mm->heading_source == HEADING_MAGNETIC && accept_data(&a->heading_magnetic_valid, mm->source, now)) {
a->heading_magnetic = mm->heading;
}
if (mm->speed_valid && mm->speed_source == SPEED_GROUNDSPEED && accept_data(&a->speed_valid, mm->source, now)) {
a->speed = mm->speed;
}
if (mm->speed_valid && mm->speed_source == SPEED_IAS && accept_data(&a->speed_ias_valid, mm->source, now)) {
a->speed_ias = mm->speed;
}
if (mm->speed_valid && mm->speed_source == SPEED_TAS && accept_data(&a->speed_tas_valid, mm->source, now)) {
a->speed_tas = mm->speed;
}
if (mm->vert_rate_valid && accept_data(&a->vert_rate_valid, mm->source, now)) {
a->vert_rate = mm->vert_rate;
a->vert_rate_source = mm->vert_rate_source;
}
if (mm->category_valid && accept_data(&a->category_valid, mm->source, now)) {
a->category = mm->category;
}
if (mm->airground != AG_INVALID && accept_data(&a->airground_valid, mm->source, now)) {
a->airground = mm->airground;
}
if (mm->callsign_valid && accept_data(&a->callsign_valid, mm->source, now)) {
memcpy(a->callsign, mm->callsign, sizeof(a->callsign));
}
// CPR, even
if (mm->cpr_valid && !mm->cpr_odd && accept_data(&a->cpr_even_valid, mm->source, now)) {
a->cpr_even_airground = mm->airground;
a->cpr_even_lat = mm->cpr_lat;
a->cpr_even_lon = mm->cpr_lon;
a->cpr_even_nuc = mm->cpr_nucp;
}
// CPR, odd
if (mm->cpr_valid && mm->cpr_odd && accept_data(&a->cpr_odd_valid, mm->source, now)) {
a->cpr_odd_airground = mm->airground;
a->cpr_odd_lat = mm->cpr_lat;
a->cpr_odd_lon = mm->cpr_lon;
a->cpr_odd_nuc = mm->cpr_nucp;
}
// Now handle derived data
// derive GNSS if we have baro + delta
if (compare_validity(&a->altitude_valid, &a->altitude_gnss_valid, now) > 0 &&
compare_validity(&a->gnss_delta_valid, &a->altitude_gnss_valid, now) > 0) {
// Baro and delta are both more recent than GNSS, derive GNSS from baro + delta
a->altitude_gnss = a->altitude + a->gnss_delta;
combine_validity(&a->altitude_gnss_valid, &a->altitude_valid, &a->gnss_delta_valid);
}
// If we've got a new cprlat or cprlon
if (mm->cpr_valid) {
updatePosition(a, mm, now);
}
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 (trackDataValid(&a->squawk_valid) && trackDataValid(&b->squawk_valid)) {
// ...check for Mode-A == Mode-S Squawk matches
if (a->squawk == b->squawk) { // 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 (trackDataValid(&a->altitude_valid) && trackDataValid(&b->altitude_valid)) {
// ... check for Mode-C == Mode-S Altitude matches
if ( (a->altitude_modeC == b->altitude_modeC ) // If a 'real' Mode-S ICAO exists at this Mode-C Altitude
|| (a->altitude_modeC == b->altitude_modeC + 1) // or this Mode-C - 100 ft
|| (a->altitude_modeC + 1 == b->altitude_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(uint64_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 {
#define EXPIRE(_f) do { if (a->_f##_valid.source != SOURCE_INVALID && now >= a->_f##_valid.expires) { a->_f##_valid.source = SOURCE_INVALID; } } while (0)
EXPIRE(callsign);
EXPIRE(altitude);
EXPIRE(altitude_gnss);
EXPIRE(gnss_delta);
EXPIRE(speed);
EXPIRE(speed_ias);
EXPIRE(speed_tas);
EXPIRE(heading);
EXPIRE(heading_magnetic);
EXPIRE(vert_rate);
EXPIRE(squawk);
EXPIRE(category);
EXPIRE(airground);
EXPIRE(cpr_odd);
EXPIRE(cpr_even);
EXPIRE(position);
prev = a; a = a->next;
}
}
}
//
// Entry point for periodic updates
//
void trackPeriodicUpdate()
{
static uint64_t next_update;
uint64_t now = mstime();
// Only do updates once per second
if (now >= next_update) {
next_update = now + 1000;
trackRemoveStaleAircraft(now);
trackUpdateAircraftModeS();
}
}
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