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// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// track.c: aircraft state tracking
//
// Copyright (c) 2014,2015 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"
/* #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;
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;
// avoid NaN
if (fabs(lat0 - lat1) < 0.0001 && fabs(lon0 - lon1) < 0.0001)
return 0.0;
return 6371e3 * acos(sin(lat0) * sin(lat1) + cos(lat0) * cos(lat1) * cos(fabs(lon0 - lon1)));
}
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, struct modesMessage *mm, double lat, double lon, uint64_t now, int surface)
{
uint64_t elapsed;
double distance;
double range;
int speed;
int inrange;
if (!(a->bFlags & MODES_ACFLAGS_LATLON_VALID))
return 1; // no reference, assume OK
elapsed = now - a->seenLatLon;
if ((mm->bFlags & MODES_ACFLAGS_SPEED_VALID) && (a->bFlags & MODES_ACFLAGS_SPEED_VALID))
speed = (mm->velocity + a->speed) / 2;
else if (mm->bFlags & MODES_ACFLAGS_SPEED_VALID)
speed = mm->velocity;
else if ((a->bFlags & MODES_ACFLAGS_SPEED_VALID) && (now - a->seenSpeed) < 30000)
speed = a->speed;
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->bFlags & MODES_ACFLAGS_LLODD_VALID) != 0;
int surface = (mm->bFlags & MODES_ACFLAGS_AOG) != 0;
*nuc = (a->even_cprnuc < a->odd_cprnuc ? a->even_cprnuc : a->odd_cprnuc); // worst of the two positions
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;
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->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) {
#ifdef DEBUG_CPR_CHECKS
if (mm->bFlags & MODES_ACFLAGS_FROM_MLAT) {
fprintf(stderr, "CPR: decode failure from MLAT (%06X) (%d).\n", a->addr, result);
fprintf(stderr, " even: %d %d odd: %d %d fflag: %s\n",
a->even_cprlat, a->even_cprlon,
a->odd_cprlat, a->odd_cprlon,
fflag ? "odd" : "even");
}
#endif
return result;
}
// for mlat results, accept it unquestioningly
if (mm->bFlags & MODES_ACFLAGS_FROM_MLAT)
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
}
}
// check speed limit
if ((a->bFlags & MODES_ACFLAGS_LATLON_VALID) && a->pos_nuc >= *nuc && !speed_check(a, mm, *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->bFlags & MODES_ACFLAGS_LLODD_VALID) != 0;
int surface = (mm->bFlags & MODES_ACFLAGS_AOG) != 0;
*nuc = mm->nuc_p;
if (a->bFlags & MODES_ACFLAGS_LATLON_REL_OK) {
reflat = a->lat;
reflon = a->lon;
if (a->pos_nuc < *nuc)
*nuc = a->pos_nuc;
} 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 = 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->raw_latitude,
mm->raw_longitude,
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 ((a->bFlags & MODES_ACFLAGS_LATLON_VALID) && a->pos_nuc >= *nuc && !speed_check(a, mm, *lat, *lon, now, surface)) {
Modes.stats_current.cpr_local_speed_checks++;
return -1;
}
return 0;
}
static void updatePosition(struct aircraft *a, struct modesMessage *mm, uint64_t now)
{
int location_result = -1;
int max_elapsed;
double new_lat = 0, new_lon = 0;
unsigned new_nuc = 0;
if (mm->bFlags & MODES_ACFLAGS_AOG)
++Modes.stats_current.cpr_surface;
else
++Modes.stats_current.cpr_airborne;
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_cprnuc = mm->nuc_p;
a->odd_cprlat = mm->raw_latitude;
a->odd_cprlon = mm->raw_longitude;
a->odd_cprtime = now;
} else {
a->even_cprnuc = mm->nuc_p;
a->even_cprlat = mm->raw_latitude;
a->even_cprlon = mm->raw_longitude;
a->even_cprtime = now;
}
// 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, now, &new_lat, &new_lon, &new_nuc);
if (location_result == -2) {
#ifdef DEBUG_CPR_CHECKS
if (mm->bFlags & MODES_ACFLAGS_FROM_MLAT) {
fprintf(stderr, "CPR failure from MLAT (%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->bFlags &= ~(MODES_ACFLAGS_LATLON_REL_OK | MODES_ACFLAGS_LLODD_VALID | MODES_ACFLAGS_LLEVEN_VALID);
// Also discard the current message's data as it is suspect - we don't want
// to update any of the aircraft state from this.
mm->bFlags &= ~(MODES_ACFLAGS_LATLON_VALID | MODES_ACFLAGS_LLODD_VALID | MODES_ACFLAGS_LLEVEN_VALID |
MODES_ACFLAGS_ALTITUDE_VALID |
MODES_ACFLAGS_SPEED_VALID |
MODES_ACFLAGS_HEADING_VALID |
MODES_ACFLAGS_NSEWSPD_VALID |
MODES_ACFLAGS_VERTRATE_VALID |
MODES_ACFLAGS_AOG_VALID |
MODES_ACFLAGS_AOG);
return;
} else if (location_result == -1) {
#ifdef DEBUG_CPR_CHECKS
if (mm->bFlags & MODES_ACFLAGS_FROM_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++;
}
}
// Otherwise try relative CPR.
if (location_result == -1) {
location_result = doLocalCPR(a, mm, now, &new_lat, &new_lon, &new_nuc);
if (location_result == -1) {
Modes.stats_current.cpr_local_skipped++;
} else {
Modes.stats_current.cpr_local_ok++;
if (a->bFlags & MODES_ACFLAGS_LATLON_REL_OK)
Modes.stats_current.cpr_local_aircraft_relative++;
else
Modes.stats_current.cpr_local_receiver_relative++;
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 = new_lat;
mm->fLon = new_lon;
// Update aircraft state
a->bFlags |= (MODES_ACFLAGS_LATLON_VALID | MODES_ACFLAGS_LATLON_REL_OK);
a->lat = new_lat;
a->lon = new_lon;
a->pos_nuc = new_nuc;
a->seenLatLon = a->seen;
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;
}
a->signalLevel[a->messages & 7] = mm->signalLevel;// replace the 8th oldest signal strength
a->seen = now;
a->messages++;
// 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);
}
// 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;
}
// If we received an altitude in a (non-mlat) DF17/18 squitter recently, ignore
// DF0/4/16/20 altitudes as single-bit errors can attribute them to the wrong
// aircraft
if ((a->bFlags & ~a->mlatFlags & MODES_ACFLAGS_ALTITUDE_VALID) &&
(now - a->seenAltitude) < 15000 &&
(a->bFlags & ~a->mlatFlags & MODES_ACFLAGS_LATLON_VALID) &&
(now - a->seenLatLon) < 15000 &&
mm->msgtype != 17 &&
mm->msgtype != 18) {
Modes.stats_current.suppressed_altitude_messages++;
} else {
a->altitude = mm->altitude;
a->modeC = (mm->altitude + 49) / 100;
a->seenAltitude = now;
}
}
// 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;
a->seenTrack = now;
}
// If a (new) SPEED has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_SPEED_VALID) {
a->speed = mm->velocity;
a->seenSpeed = now;
}
// 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 a (new) category has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_CATEGORY_VALID) {
a->category = mm->category;
}
// Update the aircrafts a->bFlags to reflect the newly received mm->bFlags;
a->bFlags |= mm->bFlags;
// Update mlat flags. The mlat flags indicate which bits in bFlags
// were last set based on a mlat-derived message.
if (mm->bFlags & MODES_ACFLAGS_FROM_MLAT)
a->mlatFlags = (a->mlatFlags & a->bFlags) | mm->bFlags;
else
a->mlatFlags = (a->mlatFlags & 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(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 {
if ((a->bFlags & MODES_ACFLAGS_LATLON_VALID) && (now - a->seenLatLon) > TRACK_AIRCRAFT_POSITION_TTL) {
/* Position is too old and no longer valid */
a->bFlags &= ~(MODES_ACFLAGS_LATLON_VALID | MODES_ACFLAGS_LATLON_REL_OK);
}
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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