VK1ET : Implement Relative CPR decoding
Modifications entirely base on code supplied by John VK1ET. Implements relative CPR Lat/Long decoding for --interactive display
This commit is contained in:
Malcolm Robb
parent
b78b60677c
commit
a04e399d7e
115
dump1090.c
115
dump1090.c
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@ -56,7 +56,7 @@
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// MinorVer changes when additional features are added, but not for bug fixes (range 00-99)
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// DayDate & Year changes for all changes, including for bug fixes. It represent the release date of the update
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//
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#define MODES_DUMP1090_VERSION "1.02.2304.13"
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#define MODES_DUMP1090_VERSION "1.02.2404.13"
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#define MODES_DEFAULT_RATE 2000000
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#define MODES_DEFAULT_FREQ 1090000000
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@ -2321,29 +2321,28 @@ int cprNFunction(double lat, int isodd) {
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return nl;
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}
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double cprDlonFunction(double lat, int isodd) {
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return 360.0 / cprNFunction(lat, isodd);
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double cprDlonFunction(double lat, int isodd, int surface) {
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return (surface ? 90.0 : 360.0) / cprNFunction(lat, 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 = 360.0 / 60;
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const double AirDlat1 = 360.0 / 59;
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void decodeCPR(struct aircraft *a, int fflag, int surface) {
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double AirDlat0 = (surface ? 90.0 : 360.0) / 60.0;
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double AirDlat1 = (surface ? 90.0 : 360.0) / 59.0;
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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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// Compute the Latitude Index "j"
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int j = (int) floor(((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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@ -2351,29 +2350,96 @@ void decodeCPR(struct aircraft *a) {
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if (rlat0 >= 270) rlat0 -= 360;
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if (rlat1 >= 270) rlat1 -= 360;
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/* Check that both are in the same latitude zone, or abort. */
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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 = (int) floor((((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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// Compute ni and the Longitude Index "m"
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if (fflag) { // Use odd packet.
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int ni = cprNFunction(rlat1,1);
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int m = (int) floor((((lon0 * (cprNLFunction(rlat1)-1)) -
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(lon1 * cprNLFunction(rlat1))) / 131072.0) + 0.5);
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a->lon = cprDlonFunction(rlat1,1) * (cprModFunction(m,ni)+lon1/131072);
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a->lon = cprDlonFunction(rlat1,1,surface) * (cprModFunction(m,ni)+lon1/131072);
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a->lat = rlat1;
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} else { // Use even packet.
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int ni = cprNFunction(rlat0,0);
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int m = (int) floor((((lon0 * (cprNLFunction(rlat0)-1)) -
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(lon1 * cprNLFunction(rlat0))) / 131072) + 0.5);
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a->lon = cprDlonFunction(rlat0, 0, surface) * (cprModFunction(m, ni)+lon0/131072);
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a->lat = rlat0;
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}
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if (a->lon > 180) a->lon -= 360;
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a->sbsflags |= MODES_SBS_LAT_LONG_FRESH;
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}
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/* This algorithm comes from:
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* 1090-WP29-07-Draft_CPR101 (which also defines decodeCPR() )
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*
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* There is an error in this document related to CPR relative decode.
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* Should use trunc() rather than the floor() function in Eq 38 and related for deltaZI.
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* floor() returns integer less than argument
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* trunc() returns integer closer to zero than argument.
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* Note: text of document describes trunc() functionality for deltaZI calculation
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* but the formulae use floor().
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*/
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int decodeCPRrelative(struct aircraft *a, int fflag, int surface, double latr, double lonr) {
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double AirDlat;
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double AirDlon;
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double lat;
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double lon;
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double rlon, rlat;
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int j,m;
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// If not passed a lat/long, we must be using aircraft relative
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if ( (latr == 0) && (lonr == 0) ) {
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latr = a->lat;
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lonr = a->lon;
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}
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if ( (latr == 0) && (lonr == 0) )
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return (-1); // Exit with error - can't do relative if we don't have ref.
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if (fflag) { // odd
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AirDlat = (surface ? 90.0 : 360.0) / 59.0;
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lat = a->odd_cprlat;
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lon = a->odd_cprlon;
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} else { // even
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AirDlat = (surface ? 90.0 : 360.0) / 60.0;
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lat = a->even_cprlat;
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lon = a->even_cprlon;
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}
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// Compute the Latitude Index "j"
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j = (int) (floor(latr/AirDlat) +
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trunc(0.5 + cprModFunction((int)latr, (int)AirDlat)/AirDlat - lat/131072));
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rlat = AirDlat * (j + lat/131072);
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if (rlat >= 270) rlat -= 360;
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// Check to see that answer is reasonable - ie no more than 1/2 cell away
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if (fabs(rlat - a->lat) > (AirDlat/2)) {
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a->lat = a->lon = 0; // This will cause a quick exit next time if no global has been done
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return (-1); // Time to give up - Latitude error
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}
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// Compute the Longitude Index "m"
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AirDlon = cprDlonFunction(rlat, fflag, 0);
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m = (int) (floor(lonr/AirDlon) +
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trunc(0.5 + cprModFunction((int)lonr, (int)AirDlon)/AirDlon - lon/131072));
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rlon = AirDlon * (m + lon/131072);
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if (rlon > 180) rlon -= 360;
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// Check to see that answer is reasonable - ie no more than 1/2 cell away
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if (fabs(rlon - a->lon) > (AirDlon/2)) {
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a->lat = a->lon = 0; // This will cause a quick exit next time if no global has been done
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return (-1); // Time to give up - Longitude error
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}
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a->lat = rlat;
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a->lon = rlon;
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a->sbsflags |= MODES_SBS_LAT_LONG_FRESH;
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return (0);
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}
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/* Receive new messages and populate the interactive mode with more info. */
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struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
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uint32_t addr;
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@ -2443,10 +2509,13 @@ struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
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a->even_cprlon = mm->raw_longitude;
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a->even_cprtime = mstime();
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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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// Try relative CPR first
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if (decodeCPRrelative(a, mm->fflag, 0, 0, 0)) {
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// If it fails then try global if the two data are less than 10 seconds apart, compute
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// the position.
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if (abs((int)(a->even_cprtime - a->odd_cprtime)) <= 10000) {
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decodeCPR(a);
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decodeCPR(a, mm->fflag, 0);
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}
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}
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} else if (mm->metype == 19) {
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if (mm->mesub == 1 || mm->mesub == 2) {
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