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Changes to prevent stale output in SBS-1 format

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The original code calculates Lat/Long only if it receives two DF-17
(subtype 9 or 18) within one second of each other. I have no idea why.
It then caches the results in the aircrafts data structure for use in
the --interactive display.

When SBS-1 style ASCII output is selected (port 30003) the code does not
attempt to calculate Lat/Long from the data just received - instead it
picks it up from the cached information in the aircraft's data
structure.

However, if the data isn't being updated this results in stale Lat/Long
being sent out. This is most likely to occur when the aircraft is at the
extreme edge of the receivers range when it may be getting some DF-17s
containing Lat/Long, but not 2 per second. The program will continue
sending the stale data until the aircraft finally times out (default 60
seconds)

I have modified the code to include a sbsflags variable in the aircraft
data structure. When a new Lat/Long is decoded and put into the
structure, a bit is set to indicate SBS_LAT_LONG_FRESH. Then, once the
Lat/Long is output the first time, the bit is cleared. Thereafter the
code will not populate the Lat/Long fields in the output message until
SBS_LAT_LONG_FRESH is set again.
This commit is contained in:
Malcolm Robb 2013-04-17 23:09:01 +01:00
parent bbcf68cf11
commit 3d25f4bf1a
1 changed files with 10 additions and 3 deletions
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13
dump1090.c
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@ -91,6 +91,8 @@
#define MODES_UNIT_FEET 0
#define MODES_UNIT_METERS 1
#define MODES_SBS_LAT_LONG_FRESH (1<<0)
#define MODES_DEBUG_DEMOD (1<<0)
#define MODES_DEBUG_DEMODERR (1<<1)
#define MODES_DEBUG_BADCRC (1<<2)
@ -142,6 +144,7 @@ struct aircraft {
int even_cprlat;
int even_cprlon;
double lat, lon; /* Coordinated obtained from CPR encoded data. */
int sbsflags;
uint64_t odd_cprtime, even_cprtime;
int squawk;
struct aircraft *next; /* Next aircraft in our linked list. */
@ -1749,6 +1752,7 @@ struct aircraft *interactiveCreateAircraft(uint32_t addr) {
a->even_cprtime = 0;
a->lat = 0;
a->lon = 0;
a->sbsflags = 0;
a->seen = time(NULL);
a->messages = 0;
a->squawk = 0;
@ -1895,6 +1899,7 @@ void decodeCPR(struct aircraft *a) {
a->lat = rlat1;
}
if (a->lon > 180) a->lon -= 360;
a->sbsflags |= MODES_SBS_LAT_LONG_FRESH;
}
/* Receive new messages and populate the interactive mode with more info. */
@ -2331,15 +2336,17 @@ void modesSendSBSOutput(struct modesMessage *mm, struct aircraft *a) {
p += sprintf(p, "MSG,1,%s,%s,,,,,,,,0,0,0,0", strCommon, mm->flight);
} else if (mm->msgtype == 17 && mm->metype >= 9 && mm->metype <= 18) {
if (a->lat == 0 && a->lon == 0)
if ( ((a->lat == 0) && (a->lon == 0)) || ((a->sbsflags & MODES_SBS_LAT_LONG_FRESH) == 0) ){
p += sprintf(p, "MSG,3,%s,,%d,,,,,,,0,0,0,0", strCommon, mm->altitude);
else
} else {
p += sprintf(p, "MSG,3,%s,,%d,,,%1.5f,%1.5f,,,0,0,0,0", strCommon, mm->altitude, a->lat, a->lon);
a->sbsflags &= ~MODES_SBS_LAT_LONG_FRESH;
}
} else if (mm->msgtype == 17 && mm->metype == 19 && mm->mesub == 1) {
int vr = (mm->vert_rate_sign==0?1:-1) * (mm->vert_rate-1) * 64;
p += sprintf(p, "MSG,4,%s,,,%d,%d,,,%i,,0,0,0,0", strCommon, a->speed, a->track, vr);
p += sprintf(p, "MSG,4,%s,,,%d,%d,,,%i,,0,0,0,0", strCommon, mm->velocity, mm->heading, vr);
} else if (mm->msgtype == 21) {
p += sprintf(p, "MSG,6,%s,,,,,,,,%d,%d,%d,%d,%d", strCommon, mm->identity, alert, emergency, spi, ground);