[hamradio-commits] [dump1090] 106/389: VK1ET : Implement Relative CPR decoding
Matthew Ernisse
mernisse-guest at moszumanska.debian.org
Wed Nov 5 00:19:45 UTC 2014
This is an automated email from the git hooks/post-receive script.
mernisse-guest pushed a commit to branch master
in repository dump1090.
commit a04e399d7e45a146afe3279d5f02ca6c5e64f387
Author: Malcolm Robb <Support at ATTAvionics.com>
Date: Wed Apr 24 20:24:46 2013 +0100
VK1ET : Implement Relative CPR decoding
Modifications entirely base on code supplied by John VK1ET.
Implements relative CPR Lat/Long decoding for --interactive display
---
dump1090.c | 119 ++++++++++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 94 insertions(+), 25 deletions(-)
diff --git a/dump1090.c b/dump1090.c
index e236563..f25d1e2 100644
--- a/dump1090.c
+++ b/dump1090.c
@@ -56,7 +56,7 @@
// MinorVer changes when additional features are added, but not for bug fixes (range 00-99)
// DayDate & Year changes for all changes, including for bug fixes. It represent the release date of the update
//
-#define MODES_DUMP1090_VERSION "1.02.2304.13"
+#define MODES_DUMP1090_VERSION "1.02.2404.13"
#define MODES_DEFAULT_RATE 2000000
#define MODES_DEFAULT_FREQ 1090000000
@@ -2321,59 +2321,125 @@ int cprNFunction(double lat, int isodd) {
return nl;
}
-double cprDlonFunction(double lat, int isodd) {
- return 360.0 / cprNFunction(lat, isodd);
+double cprDlonFunction(double lat, int isodd, int surface) {
+ return (surface ? 90.0 : 360.0) / cprNFunction(lat, isodd);
}
/* This algorithm comes from:
* http://www.lll.lu/~edward/edward/adsb/DecodingADSBposition.html.
*
- *
* A few remarks:
* 1) 131072 is 2^17 since CPR latitude and longitude are encoded in 17 bits.
* 2) We assume that we always received the odd packet as last packet for
* simplicity. This may provide a position that is less fresh of a few
* seconds.
*/
-void decodeCPR(struct aircraft *a) {
- const double AirDlat0 = 360.0 / 60;
- const double AirDlat1 = 360.0 / 59;
+void decodeCPR(struct aircraft *a, int fflag, int surface) {
+ double AirDlat0 = (surface ? 90.0 : 360.0) / 60.0;
+ double AirDlat1 = (surface ? 90.0 : 360.0) / 59.0;
double lat0 = a->even_cprlat;
double lat1 = a->odd_cprlat;
double lon0 = a->even_cprlon;
double lon1 = a->odd_cprlon;
- /* Compute the Latitude Index "j" */
- int j = (int) floor(((59*lat0 - 60*lat1) / 131072) + 0.5);
+ // Compute the Latitude Index "j"
+ int j = (int) floor(((59*lat0 - 60*lat1) / 131072) + 0.5);
double rlat0 = AirDlat0 * (cprModFunction(j,60) + lat0 / 131072);
double rlat1 = AirDlat1 * (cprModFunction(j,59) + lat1 / 131072);
if (rlat0 >= 270) rlat0 -= 360;
if (rlat1 >= 270) rlat1 -= 360;
- /* Check that both are in the same latitude zone, or abort. */
+ // Check that both are in the same latitude zone, or abort.
if (cprNLFunction(rlat0) != cprNLFunction(rlat1)) return;
- /* Compute ni and the longitude index m */
- if (a->even_cprtime > a->odd_cprtime) {
- /* Use even packet. */
- int ni = cprNFunction(rlat0,0);
- int m = (int) floor((((lon0 * (cprNLFunction(rlat0)-1)) -
- (lon1 * cprNLFunction(rlat0))) / 131072) + 0.5);
- a->lon = cprDlonFunction(rlat0,0) * (cprModFunction(m,ni)+lon0/131072);
- a->lat = rlat0;
- } else {
- /* Use odd packet. */
+ // Compute ni and the Longitude Index "m"
+ if (fflag) { // Use odd packet.
int ni = cprNFunction(rlat1,1);
int m = (int) floor((((lon0 * (cprNLFunction(rlat1)-1)) -
(lon1 * cprNLFunction(rlat1))) / 131072.0) + 0.5);
- a->lon = cprDlonFunction(rlat1,1) * (cprModFunction(m,ni)+lon1/131072);
+ a->lon = cprDlonFunction(rlat1,1,surface) * (cprModFunction(m,ni)+lon1/131072);
a->lat = rlat1;
+ } else { // Use even packet.
+ int ni = cprNFunction(rlat0,0);
+ int m = (int) floor((((lon0 * (cprNLFunction(rlat0)-1)) -
+ (lon1 * cprNLFunction(rlat0))) / 131072) + 0.5);
+ a->lon = cprDlonFunction(rlat0, 0, surface) * (cprModFunction(m, ni)+lon0/131072);
+ a->lat = rlat0;
}
if (a->lon > 180) a->lon -= 360;
+
a->sbsflags |= MODES_SBS_LAT_LONG_FRESH;
}
+/* This algorithm comes from:
+ * 1090-WP29-07-Draft_CPR101 (which also defines decodeCPR() )
+ *
+ * There is an error in this document related to CPR relative decode.
+ * Should use trunc() rather than the floor() function in Eq 38 and related for deltaZI.
+ * floor() returns integer less than argument
+ * trunc() returns integer closer to zero than argument.
+ * Note: text of document describes trunc() functionality for deltaZI calculation
+ * but the formulae use floor().
+ */
+int decodeCPRrelative(struct aircraft *a, int fflag, int surface, double latr, double lonr) {
+ double AirDlat;
+ double AirDlon;
+ double lat;
+ double lon;
+ double rlon, rlat;
+ int j,m;
+
+ // If not passed a lat/long, we must be using aircraft relative
+ if ( (latr == 0) && (lonr == 0) ) {
+ latr = a->lat;
+ lonr = a->lon;
+ }
+ if ( (latr == 0) && (lonr == 0) )
+ return (-1); // Exit with error - can't do relative if we don't have ref.
+
+ if (fflag) { // odd
+ AirDlat = (surface ? 90.0 : 360.0) / 59.0;
+ lat = a->odd_cprlat;
+ lon = a->odd_cprlon;
+ } else { // even
+ AirDlat = (surface ? 90.0 : 360.0) / 60.0;
+ lat = a->even_cprlat;
+ lon = a->even_cprlon;
+ }
+
+ // Compute the Latitude Index "j"
+ j = (int) (floor(latr/AirDlat) +
+ trunc(0.5 + cprModFunction((int)latr, (int)AirDlat)/AirDlat - lat/131072));
+ rlat = AirDlat * (j + lat/131072);
+ if (rlat >= 270) rlat -= 360;
+
+ // Check to see that answer is reasonable - ie no more than 1/2 cell away
+ if (fabs(rlat - a->lat) > (AirDlat/2)) {
+ a->lat = a->lon = 0; // This will cause a quick exit next time if no global has been done
+ return (-1); // Time to give up - Latitude error
+ }
+
+ // Compute the Longitude Index "m"
+ AirDlon = cprDlonFunction(rlat, fflag, 0);
+ m = (int) (floor(lonr/AirDlon) +
+ trunc(0.5 + cprModFunction((int)lonr, (int)AirDlon)/AirDlon - lon/131072));
+ rlon = AirDlon * (m + lon/131072);
+ if (rlon > 180) rlon -= 360;
+
+ // Check to see that answer is reasonable - ie no more than 1/2 cell away
+ if (fabs(rlon - a->lon) > (AirDlon/2)) {
+ a->lat = a->lon = 0; // This will cause a quick exit next time if no global has been done
+ return (-1); // Time to give up - Longitude error
+ }
+
+ a->lat = rlat;
+ a->lon = rlon;
+ a->sbsflags |= MODES_SBS_LAT_LONG_FRESH;
+
+ return (0);
+}
+
/* Receive new messages and populate the interactive mode with more info. */
struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
uint32_t addr;
@@ -2443,10 +2509,13 @@ struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
a->even_cprlon = mm->raw_longitude;
a->even_cprtime = mstime();
}
- /* If the two data is less than 10 seconds apart, compute
- * the position. */
- if (abs((int)(a->even_cprtime - a->odd_cprtime)) <= 10000) {
- decodeCPR(a);
+ // Try relative CPR first
+ if (decodeCPRrelative(a, mm->fflag, 0, 0, 0)) {
+ // If it fails then try global if the two data are less than 10 seconds apart, compute
+ // the position.
+ if (abs((int)(a->even_cprtime - a->odd_cprtime)) <= 10000) {
+ decodeCPR(a, mm->fflag, 0);
+ }
}
} else if (mm->metype == 19) {
if (mm->mesub == 1 || mm->mesub == 2) {
--
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