CPR position decoding. Track calculation from velocity components.
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antirez
parent
ec1f34f572
commit
b6907f400a
190
dump1090.c
190
dump1090.c
@ -85,8 +85,17 @@ struct aircraft {
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char flight[9]; /* Flight number */
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int altitude; /* Altitude */
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int speed; /* Velocity computed from EW and NS components. */
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int track; /* Angle of flight. */
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time_t seen; /* Time at which the last packet was received. */
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long messages; /* Number of Mode S messages received. */
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/* Encoded latitude and longitude as extracted by odd and even
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* CPR encoded messages. */
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int odd_cprlat;
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int odd_cprlon;
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int even_cprlat;
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int even_cprlon;
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double lat, lon; /* Coordinated obtained from CPR encoded data. */
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time_t odd_cprtime, even_cprtime;
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struct aircraft *next; /* Next aircraft in our linked list. */
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};
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@ -157,14 +166,14 @@ struct modesMessage {
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int heading_is_valid;
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int heading;
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int aircraft_type;
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int fflag; /* Odd or Even CPR message? */
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int fflag; /* 1 = Odd, 0 = Even CPR message. */
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int tflag; /* UTC synchronized? */
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int raw_latitude; /* Non decoded latitude */
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int raw_longitude; /* Non decoded longitude */
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char flight[9]; /* 8 chars flight number. */
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int ew_dir; /* E/W direction. */
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int ew_dir; /* 0 = East, 1 = West. */
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int ew_velocity; /* E/W velocity. */
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int ns_dir; /* N/S direction. */
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int ns_dir; /* 0 = North, 1 = South. */
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int ns_velocity; /* N/S velocity. */
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int vert_rate_source; /* Vertical rate source. */
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int vert_rate_sign; /* Vertical rate sign. */
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@ -867,8 +876,24 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
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mm->vert_rate_source = (msg[8]&0x10) >> 4;
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mm->vert_rate_sign = (msg[8]&0x8) >> 5;
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mm->vert_rate = ((msg[8]&7) << 6) | ((msg[9]&0xfc) >> 2);
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/* Compute velocity and angle from the two speed
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* components. */
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mm->velocity = sqrt(mm->ns_velocity*mm->ns_velocity+
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mm->ew_velocity*mm->ew_velocity);
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if (mm->velocity) {
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int ewv = mm->ew_velocity;
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int nsv = mm->ns_velocity;
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double heading;
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if (mm->ew_dir) ewv *= -1;
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if (mm->ns_dir) nsv *= -1;
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heading = atan2(ewv,nsv);
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/* Convert to degrees. */
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mm->heading = heading * 360 / (M_PI*2);
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/* We don't want negative values but a 0-360 scale. */
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if (mm->heading < 0) mm->heading += 360;
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}
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} else if (mm->mesub == 3 || mm->mesub == 4) {
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mm->heading_is_valid = msg[5] & (1<<2);
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mm->heading = (360.0/128) * (((msg[5] & 3) << 5) |
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@ -1207,6 +1232,15 @@ struct aircraft *interactiveCreateAircraft(uint32_t addr) {
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a->flight[0] = '\0';
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a->altitude = 0;
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a->speed = 0;
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a->track = 0;
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a->odd_cprlat = 0;
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a->odd_cprlon = 0;
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a->odd_cprtime = 0;
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a->even_cprlat = 0;
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a->even_cprlon = 0;
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a->even_cprtime = 0;
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a->lat = 0;
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a->lon = 0;
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a->seen = time(NULL);
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a->messages = 0;
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a->next = NULL;
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@ -1225,6 +1259,130 @@ struct aircraft *interactiveFindAircraft(uint32_t addr) {
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return NULL;
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}
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/* Always positive MOD operation, used for CPR decoding. */
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int cprModFunction(int a, int b) {
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int res = a % b;
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if (res < 0) res += b;
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return res;
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}
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/* The NL function uses the precomputed table from 1090-WP-9-14 */
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int cprNLFunction(double lat) {
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if (lat < 10.47047130) return 59;
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if (lat < 14.82817437) return 58;
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if (lat < 18.18626357) return 57;
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if (lat < 21.02939493) return 56;
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if (lat < 23.54504487) return 55;
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if (lat < 25.82924707) return 54;
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if (lat < 27.93898710) return 53;
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if (lat < 29.91135686) return 52;
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if (lat < 31.77209708) return 51;
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if (lat < 33.53993436) return 50;
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if (lat < 35.22899598) return 49;
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if (lat < 36.85025108) return 48;
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if (lat < 38.41241892) return 47;
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if (lat < 39.92256684) return 46;
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if (lat < 41.38651832) return 45;
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if (lat < 42.80914012) return 44;
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if (lat < 44.19454951) return 43;
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if (lat < 45.54626723) return 42;
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if (lat < 46.86733252) return 41;
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if (lat < 48.16039128) return 40;
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if (lat < 49.42776439) return 39;
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if (lat < 50.67150166) return 38;
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if (lat < 51.89342469) return 37;
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if (lat < 53.09516153) return 36;
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if (lat < 54.27817472) return 35;
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if (lat < 55.44378444) return 34;
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if (lat < 56.59318756) return 33;
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if (lat < 57.72747354) return 32;
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if (lat < 58.84763776) return 31;
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if (lat < 59.95459277) return 30;
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if (lat < 61.04917774) return 29;
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if (lat < 62.13216659) return 28;
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if (lat < 63.20427479) return 27;
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if (lat < 64.26616523) return 26;
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if (lat < 65.31845310) return 25;
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if (lat < 66.36171008) return 24;
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if (lat < 67.39646774) return 23;
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if (lat < 68.42322022) return 22;
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if (lat < 69.44242631) return 21;
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if (lat < 70.45451075) return 20;
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if (lat < 71.45986473) return 19;
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if (lat < 72.45884545) return 18;
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if (lat < 73.45177442) return 17;
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if (lat < 74.43893416) return 16;
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if (lat < 75.42056257) return 15;
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if (lat < 76.39684391) return 14;
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if (lat < 77.36789461) return 13;
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if (lat < 78.33374083) return 12;
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if (lat < 79.29428225) return 11;
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if (lat < 80.24923213) return 10;
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if (lat < 81.19801349) return 9;
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if (lat < 82.13956981) return 8;
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if (lat < 83.07199445) return 7;
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if (lat < 83.99173563) return 6;
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if (lat < 84.89166191) return 5;
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if (lat < 85.75541621) return 4;
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if (lat < 86.53536998) return 3;
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if (lat < 87.00000000) return 2;
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else return 1;
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}
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int cprNFunction(int i, int isodd) {
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int nl = cprNLFunction(i) - isodd;
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if (nl < 1) nl = 1;
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return nl;
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}
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double cprDlonFunction(int i, int isodd) {
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return 360.0 / cprNFunction(i, isodd);
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}
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/* This algorithm comes from:
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* http://www.lll.lu/~edward/edward/adsb/DecodingADSBposition.html.
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*
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*
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* A few remarks:
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* 1) 131072 is 2^17 since CPR latitude and longitude are encoded in 17 bits.
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* 2) We assume that we always received the odd packet as last packet for
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* simplicity. This may provide a position that is less fresh of a few
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* seconds.
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*/
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void decodeCPR(struct aircraft *a) {
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const double AirDlat0 = 6;
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const double AirDlat1 = 360.0 / 59;
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double lat0 = a->even_cprlat;
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double lat1 = a->odd_cprlat;
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double lon0 = a->even_cprlon;
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double lon1 = a->odd_cprlon;
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/* Compute the Latitude Index "j" */
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int j = ((59*lat0 - 60*lat1) / 131072) + 0.5;
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double rlat0 = AirDlat0 * (cprModFunction(j,60) + lat0 / 131072);
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double rlat1 = AirDlat1 * (cprModFunction(j,59) + lat1 / 131072);
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/* Check that both are in the same latitude zone, or abort. */
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if (cprNLFunction(rlat0) != cprNLFunction(rlat1)) return;
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/* Compute ni and the longitude index m */
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if (a->even_cprtime > a->odd_cprtime) {
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/* Use even packet. */
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int ni = cprNFunction(rlat0,0);
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int m = (((lon0 * (cprNLFunction(rlat0)-1)) -
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(lon1 * cprNLFunction(rlat0))) / 131072) + 0.5;
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a->lon = cprDlonFunction(rlat0,0) * (cprModFunction(m,ni)+lon0/131072);
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a->lat = rlat0;
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} else {
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/* Use odd packet. */
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int ni = cprNFunction(rlat1,1);
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int m = (((lon0 * (cprNLFunction(rlat1)-1)) -
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(lon1 * cprNLFunction(rlat1))) / 131072) + 0.5;
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a->lon = cprDlonFunction(rlat1,1) * (cprModFunction(m,ni)+lon1/131072);
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a->lat = rlat1;
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}
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}
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/* Receive new messages and populate the interactive mode with more info. */
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void interactiveReceiveData(struct modesMessage *mm) {
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uint32_t addr;
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@ -1268,9 +1426,23 @@ void interactiveReceiveData(struct modesMessage *mm) {
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memcpy(a->flight, mm->flight, sizeof(a->flight));
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} else if (mm->metype >= 9 && mm->metype <= 18) {
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a->altitude = mm->altitude;
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if (mm->fflag) {
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a->odd_cprlat = mm->raw_latitude;
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a->odd_cprlon = mm->raw_longitude;
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a->odd_cprtime = a->seen; /* Current time. */
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} else {
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a->even_cprlat = mm->raw_latitude;
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a->even_cprlon = mm->raw_longitude;
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a->even_cprtime = a->seen; /* Current time. */
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}
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/* If the two data is less than 10 seconds apart, compute
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* the position. */
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if (abs(a->even_cprtime - a->odd_cprtime) <= 10)
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decodeCPR(a);
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} else if (mm->metype == 19) {
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if (mm->mesub == 1 || mm->mesub == 2) {
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a->speed = mm->velocity;
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a->track = mm->heading;
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}
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}
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}
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@ -1288,9 +1460,10 @@ void interactiveShowData(void) {
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progress[3] = '\0';
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printf("\x1b[H\x1b[2J"); /* Clear the screen */
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printf("Hex Flight Altitude Speed Messages Seen %s\n",
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progress);
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printf("-------------------------------------------------------\n");
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printf(
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"Hex Flight Altitude Speed Lat Lon Track Messages Seen %s\n"
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"--------------------------------------------------------------------------------\n",
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progress);
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while(a && count < Modes.interactive_rows) {
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int altitude = a->altitude, speed = a->speed;
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@ -1301,8 +1474,9 @@ void interactiveShowData(void) {
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speed *= 1.852;
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}
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printf("%-6s %-8s %-9d %-9d %-9ld %d sec ago\n",
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a->hexaddr, a->flight, altitude, speed, a->messages,
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printf("%-6s %-8s %-9d %-7d %-7.03f %-7.03f %-3d %-9ld %d sec\n",
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a->hexaddr, a->flight, altitude, speed,
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a->lat, a->lon, a->track, a->messages,
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(int)(now - a->seen));
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a = a->next;
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count++;
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