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track.c
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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 */
uint32_t modeAC_count[4096];
uint32_t modeAC_lastcount[4096];
uint32_t modeAC_match[4096];
uint32_t modeAC_age[4096];
//
// 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;
// defaults until we see a message otherwise
a->adsb_version = -1;
a->adsb_hrd = HEADING_MAGNETIC;
a->adsb_tah = HEADING_GROUND_TRACK;
// prime FATSV defaults we only emit on change
// start off with the "last emitted" ACAS RA being blank (just the BDS 3,0
// or ES type code)
a->fatsv_emitted_bds_30[0] = 0x30;
a->fatsv_emitted_es_acas_ra[0] = 0xE2;
a->fatsv_emitted_adsb_version = -1;
a->fatsv_emitted_addrtype = ADDR_UNKNOWN;
// don't immediately emit, let some data build up
a->fatsv_last_emitted = a->fatsv_last_force_emit = messageNow();
// Copy the first message so we can emit it later when a second message arrives.
a->first_message = *mm;
// initialize data validity ages
#define F(f,s,e) do { a->f##_valid.stale_interval = (s) * 1000; a->f##_valid.expire_interval = (e) * 1000; } while (0)
F(callsign, 60, 70); // ADS-B or Comm-B
F(altitude_baro, 15, 70); // ADS-B or Mode S
F(altitude_geom, 60, 70); // ADS-B only
F(geom_delta, 60, 70); // ADS-B only
F(gs, 60, 70); // ADS-B or Comm-B
F(ias, 60, 70); // ADS-B (rare) or Comm-B
F(tas, 60, 70); // ADS-B (rare) or Comm-B
F(mach, 60, 70); // Comm-B only
F(track, 60, 70); // ADS-B or Comm-B
F(track_rate, 60, 70); // Comm-B only
F(roll, 60, 70); // Comm-B only
F(mag_heading, 60, 70); // ADS-B (rare) or Comm-B
F(true_heading, 60, 70); // ADS-B only (rare)
F(baro_rate, 60, 70); // ADS-B or Comm-B
F(geom_rate, 60, 70); // ADS-B or Comm-B
F(squawk, 15, 70); // ADS-B or Mode S
F(airground, 15, 70); // ADS-B or Mode S
F(nav_qnh, 60, 70); // Comm-B only
F(nav_altitude_mcp, 60, 70); // ADS-B or Comm-B
F(nav_altitude_fms, 60, 70); // ADS-B or Comm-B
F(nav_altitude_src, 60, 70); // ADS-B or Comm-B
F(nav_heading, 60, 70); // ADS-B or Comm-B
F(nav_modes, 60, 70); // ADS-B or Comm-B
F(cpr_odd, 60, 70); // ADS-B only
F(cpr_even, 60, 70); // ADS-B only
F(position, 60, 70); // ADS-B only
F(nic_a, 60, 70); // ADS-B only
F(nic_c, 60, 70); // ADS-B only
F(nic_baro, 60, 70); // ADS-B only
F(nac_p, 60, 70); // ADS-B only
F(nac_v, 60, 70); // ADS-B only
F(sil, 60, 70); // ADS-B only
F(gva, 60, 70); // ADS-B only
F(sda, 60, 70); // ADS-B only
#undef F
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)
{
if (messageNow() < d->updated)
return 0;
if (source < d->source && messageNow() < d->stale)
return 0;
d->source = source;
d->updated = messageNow();
d->stale = messageNow() + (d->stale_interval ? d->stale_interval : 60000);
d->expires = messageNow() + (d->expire_interval ? d->expire_interval : 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) {
if (messageNow() < lhs->stale && lhs->source > rhs->source)
return 1;
else if (messageNow() < 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, 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);
if (trackDataValid(&a->gs_valid))
speed = a->gs;
else if (trackDataValid(&a->tas_valid))
speed = a->tas * 4 / 3;
else if (trackDataValid(&a->ias_valid))
speed = a->ias * 2;
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;
}
// return 1 if left_rc is worse (less accurate) than right_rc
static int rcIsWorse(int left_rc, int right_rc)
{
if (left_rc == 0 && right_rc == 0) // both unknown
return 0;
if (left_rc == 0)
return 1; // left unknown < right known
if (right_rc == 0)
return 0; // left known > right unknown
return (left_rc > right_rc);
}
static int doGlobalCPR(struct aircraft *a, struct modesMessage *mm, double *lat, double *lon, unsigned *nic, unsigned *rc)
{
int result;
int fflag = mm->cpr_odd;
int surface = (mm->cpr_type == CPR_SURFACE);
// derive NIC, Rc from the worse of the two position
// smaller NIC is worse
*nic = (a->cpr_even_nic < a->cpr_odd_nic ? a->cpr_even_nic : a->cpr_odd_nic);
*rc = (rcIsWorse(a->cpr_even_rc, a->cpr_odd_rc) ? a->cpr_even_rc : a->cpr_odd_rc);
if (surface) {
// surface global CPR
// find reference location
double reflat, reflon;
if (trackDataValid(&a->position_valid)) { // 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->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_nic >= *nic && !rcIsWorse(a->pos_rc, *rc) && !speed_check(a, *lat, *lon, surface)) {
Modes.stats_current.cpr_global_speed_checks++;
return -2;
}
return result;
}
static int doLocalCPR(struct aircraft *a, struct modesMessage *mm, double *lat, double *lon, unsigned *nic, unsigned *rc)
{
// relative CPR
// find reference location
double reflat, reflon;
double range_limit = 0;
int result;
int fflag = mm->cpr_odd;
int surface = (mm->cpr_type == CPR_SURFACE);
if (fflag) {
*nic = a->cpr_odd_nic;
*rc = a->cpr_odd_rc;
} else {
*nic = a->cpr_even_nic;
*rc = a->cpr_even_rc;
}
if (trackDataValid(&a->position_valid)) {
reflat = a->lat;
reflon = a->lon;
if (a->pos_nic < *nic)
*nic = a->pos_nic;
if (rcIsWorse(a->pos_rc, *rc))
*rc = a->pos_rc;
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_nic >= *nic && !rcIsWorse(a->pos_rc, *rc) && !speed_check(a, *lat, *lon, 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)
{
int location_result = -1;
uint64_t max_elapsed;
double new_lat = 0, new_lon = 0;
unsigned new_nic = 0;
unsigned new_rc = 0;
int surface;
surface = (mm->cpr_type == CPR_SURFACE);
if (surface) {
++Modes.stats_current.cpr_surface;
// Surface: 25 seconds if >25kt or speed unknown, 50 seconds otherwise
if (mm->gs_valid && mm->gs.selected <= 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_type == a->cpr_even_type &&
time_between(a->cpr_odd_valid.updated, a->cpr_even_valid.updated) <= max_elapsed) {
location_result = doGlobalCPR(a, mm, &new_lat, &new_lon, &new_nic, &new_rc);
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, &new_lat, &new_lon, &new_nic, &new_rc);
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;
mm->decoded_nic = new_nic;
mm->decoded_rc = new_rc;
// Update aircraft state
a->lat = new_lat;
a->lon = new_lon;
a->pos_nic = new_nic;
a->pos_rc = new_rc;
update_range_histogram(new_lat, new_lon);
}
}
static unsigned compute_nic(unsigned metype, unsigned version, unsigned nic_a, unsigned nic_b, unsigned nic_c)
{
switch (metype) {
case 5: // surface
case 9: // airborne
case 20: // airborne, GNSS altitude
return 11;
case 6: // surface
case 10: // airborne
case 21: // airborne, GNSS altitude
return 10;
case 7: // surface
if (version == 2) {
if (nic_a && !nic_c) {
return 9;
} else {
return 8;
}
} else if (version == 1) {
if (nic_a) {
return 9;
} else {
return 8;
}
} else {
return 8;
}
case 8: // surface
if (version == 2) {
if (nic_a && nic_c) {
return 7;
} else if (nic_a && !nic_c) {
return 6;
} else if (!nic_a && nic_c) {
return 6;
} else {
return 0;
}
} else {
return 0;
}
case 11: // airborne
if (version == 2) {
if (nic_a && nic_b) {
return 9;
} else {
return 8;
}
} else if (version == 1) {
if (nic_a) {
return 9;
} else {
return 8;
}
} else {
return 8;
}
case 12: // airborne
return 7;
case 13: // airborne
return 6;
case 14: // airborne
return 5;
case 15: // airborne
return 4;
case 16: // airborne
if (nic_a && nic_b) {
return 3;
} else {
return 2;
}
case 17: // airborne
return 1;
default:
return 0;
}
}
static unsigned compute_rc(unsigned metype, unsigned version, unsigned nic_a, unsigned nic_b, unsigned nic_c)
{
// ED-102 Table 2-14, Table N-4, Table N-11
switch (metype) {
case 5: // surface
case 9: // airborne
case 20: // airborne, GNSS altitude
return 8; // 7.5m
case 6: // surface
case 10: // airborne
case 21: // airborne, GNSS altitude
return 25;
case 7: // surface
if (version == 2) {
if (nic_a && !nic_c) {
return 75;
} else {
return 186; // 185.2m, 0.1NM
}
} else if (version == 1) {
if (nic_a) {
return 75;
} else {
return 186; // 185.2m, 0.1NM
}
} else {
return 186; // 185.2m, 0.1NM
}
case 8: // surface
if (version == 2) {
if (nic_a && nic_c) {
return 371; // 370.4m, 0.2NM
} else if (nic_a && !nic_c) {
return 556; // 555.6m, 0.3NM
} else if (!nic_a && nic_c) {
return 1111; // 1111m, 0.6NM
} else {
return RC_UNKNOWN;
}
} else {
return RC_UNKNOWN;
}
case 11: // airborne
if (version == 2) {
if (nic_a && nic_b) {
return 75;
} else {
return 186; // 185.2m, 0.1NM
}
} else if (version == 1) {
if (nic_a) {
return 75;
} else {
return 186; // 185.2m, 0.1NM
}
} else {
return 186; // 185.2m, 0.1NM
}
case 12: // airborne
return 371; // 370.4m, 0.2NM
case 13: // airborne
if (version == 2) {
if (!nic_a && nic_b) {
return 556; // 555.6m, 0.3NM
} else if (!nic_a && !nic_b) {
return 926; // 926m, 0.5NM
} else if (nic_a && nic_b) {
return 1112; // 1111.2m, 0.6NM
} else {
return RC_UNKNOWN; // bad combination
}
} else if (version == 1) {
if (nic_a) {
return 1112; // 1111.2m, 0.6NM
} else {
return 926; // 926m, 0.5NM
}
} else {
return 926; // 926m, 0.5NM
}
case 14: // airborne
return 1852; // 1.0NM
case 15: // airborne
return 3704; // 2NM
case 16: // airborne
if (version == 2) {
if (nic_a && nic_b) {
return 7408; // 4NM
} else {
return 14816; // 8NM
}
} else if (version == 1) {
if (nic_a) {
return 7408; // 4NM
} else {
return 14816; // 8NM
}
} else {
return 18520; // 10NM
}
case 17: // airborne
return 37040; // 20NM
default:
return RC_UNKNOWN;
}
}
// Map ADS-B v0 position message type to NACp value
// returned computed NACp, or -1 if not a suitable message type
static int compute_v0_nacp(struct modesMessage *mm)
{
if (mm->msgtype != 17 && mm->msgtype != 18) {
return -1;
}
// ED-102A Table N-7
switch (mm->metype) {
case 0: return 0;
case 5: return 11;
case 6: return 10;
case 7: return 8;
case 8: return 0;
case 9: return 11;
case 10: return 10;
case 11: return 8;
case 12: return 7;
case 13: return 6;
case 14: return 5;
case 15: return 4;
case 16: return 1;
case 17: return 1;
case 18: return 0;
case 20: return 11;
case 21: return 10;
case 22: return 0;
default: return -1;
}
}
// Map ADS-B v0 position message type to SIL value
// returned computed SIL, or -1 if not a suitable message type
static int compute_v0_sil(struct modesMessage *mm)
{
if (mm->msgtype != 17 && mm->msgtype != 18) {
return -1;
}
// ED-102A Table N-8
switch (mm->metype) {
case 0:
return 0;
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
case 11:
case 12:
case 13:
case 14:
case 15:
case 16:
case 17:
return 2;
case 18:
return 0;
case 20:
case 21:
return 2;
case 22:
return 0;
default:
return -1;
}
}
static void compute_nic_rc_from_message(struct modesMessage *mm, struct aircraft *a, unsigned *nic, unsigned *rc)
{
int nic_a = (trackDataValid(&a->nic_a_valid) && a->nic_a);
int nic_b = (mm->accuracy.nic_b_valid && mm->accuracy.nic_b);
int nic_c = (trackDataValid(&a->nic_c_valid) && a->nic_c);
*nic = compute_nic(mm->metype, a->adsb_version, nic_a, nic_b, nic_c);
*rc = compute_rc(mm->metype, a->adsb_version, nic_a, nic_b, nic_c);
}
static int altitude_to_feet(int raw, altitude_unit_t unit)
{
switch (unit) {
case UNIT_METERS:
return raw / 0.3048;
case UNIT_FEET:
return raw;
default:
return 0;
}
}
//
//=========================================================================
//
// Receive new messages and update tracked aircraft state
//
struct aircraft *trackUpdateFromMessage(struct modesMessage *mm)
{
struct aircraft *a;
if (mm->msgtype == 32) {
// Mode A/C, just count it (we ignore SPI)
modeAC_count[modeAToIndex(mm->squawk)]++;
return NULL;
}
if (mm->addr == 0) {
// junk address, don't track it
return NULL;
}
_messageNow = mm->sysTimestampMsg;
// 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 = messageNow();
a->messages++;
// update addrtype, we only ever go towards "more direct" types
if (mm->addrtype < a->addrtype)
a->addrtype = mm->addrtype;
// if we saw some direct ADS-B for the first time, assume version 0
if (mm->source == SOURCE_ADSB && a->adsb_version < 0)
a->adsb_version = 0;
// category shouldn't change over time, don't bother with metadata
if (mm->category_valid) {
a->category = mm->category;
}
// operational status message
// done early to update version / HRD / TAH
if (mm->opstatus.valid) {
a->adsb_version = mm->opstatus.version;
if (mm->opstatus.hrd != HEADING_INVALID) {
a->adsb_hrd = mm->opstatus.hrd;
}
if (mm->opstatus.tah != HEADING_INVALID) {
a->adsb_tah = mm->opstatus.tah;
}
}
// fill in ADS-B v0 NACp, SIL from position message type
if (a->adsb_version == 0 && !mm->accuracy.nac_p_valid) {
int computed_nacp = compute_v0_nacp(mm);
if (computed_nacp != -1) {
mm->accuracy.nac_p_valid = 1;
mm->accuracy.nac_p = computed_nacp;
}
}
if (a->adsb_version == 0 && mm->accuracy.sil_type == SIL_INVALID) {
int computed_sil = compute_v0_sil(mm);
if (computed_sil != -1) {
mm->accuracy.sil_type = SIL_UNKNOWN;
mm->accuracy.sil = computed_sil;
}
}
if (mm->altitude_baro_valid && accept_data(&a->altitude_baro_valid, mm->source)) {
int alt = altitude_to_feet(mm->altitude_baro, mm->altitude_baro_unit);
if (a->modeC_hit) {
int new_modeC = (a->altitude_baro + 49) / 100;
int old_modeC = (alt + 49) / 100;
if (new_modeC != old_modeC) {
a->modeC_hit = 0;
}
}
a->altitude_baro = alt;
}
if (mm->squawk_valid && accept_data(&a->squawk_valid, mm->source)) {
if (mm->squawk != a->squawk) {
a->modeA_hit = 0;
}
a->squawk = mm->squawk;
#if 0 // Disabled for now as it obscures the origin of the data
// Handle 7x00 without a corresponding emergency status
if (!mm->emergency_valid) {
emergency_t squawk_emergency;
switch (mm->squawk) {
case 0x7500:
squawk_emergency = EMERGENCY_UNLAWFUL;
break;
case 0x7600:
squawk_emergency = EMERGENCY_NORDO;