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Better decoding of DF-17 Airborne Velocity

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Based on a submission by VK1ET. Fully decode DF-17, metype 19. Take care
to only update fields that are valid in the data.

Also, initialise (to zero) the mm structures before use
This commit is contained in:
Malcolm Robb 2013-05-08 22:16:38 +01:00
parent 6af4bb7431
commit 8048cbec6b
1 changed files with 58 additions and 30 deletions
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88
dump1090.c
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@ -272,7 +272,7 @@ struct modesMessage {
int metype; // Extended squitter message type.
int mesub; // Extended squitter message subtype.
int heading_is_valid;
int heading;
int heading; // Reported by aircraft, or computed from from EW and NS velocity
int fflag; // 1 = Odd, 0 = Even CPR message.
int tflag; // UTC synchronized?
int raw_latitude; // Non decoded latitude.
@ -285,7 +285,8 @@ struct modesMessage {
int vert_rate_source; // Vertical rate source.
int vert_rate_sign; // Vertical rate sign.
int vert_rate; // Vertical rate.
int velocity; // Computed from EW and NS velocity.
int velocity; // Reported by aircraft, or computed from from EW and NS velocity
int tasflag; // TAS or IAS
// DF4, DF5, DF20, DF21
int fs; // Flight status for DF4,5,20,21
@ -1454,39 +1455,63 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
}
} else if (mm->metype == 19) { // Airborne Velocity Message
if (mm->mesub == 1 || mm->mesub == 2) {
mm->ew_dir = (msg[5]&4) >> 2;
mm->ew_velocity = ((msg[5]&3) << 8) | msg[6];
mm->ns_dir = (msg[7]&0x80) >> 7;
mm->ns_velocity = ((msg[7]&0x7f) << 3) | ((msg[8]&0xe0) >> 5);
mm->vert_rate_source = (msg[8]&0x10) >> 4;
mm->vert_rate_sign = (msg[8]&0x8) >> 3;
mm->vert_rate = ((msg[8]&7) << 6) | ((msg[9]&0xfc) >> 2);
// Compute velocity and angle from the two speed components
mm->velocity = (int) sqrt(mm->ns_velocity*mm->ns_velocity +
mm->ew_velocity*mm->ew_velocity);
if ( (mm->mesub >= 1) && (mm->mesub <= 4) ) {
int vert_rate = ((msg[8] & 0x07) << 6) | (msg[9] >> 2);
if (vert_rate) {
mm->vert_rate_source = (msg[8] & 0x10) >> 4;
mm->vert_rate_sign = (msg[8] & 0x08) >> 3;
mm->vert_rate = vert_rate - 1;
}
}
if (mm->velocity) {
int ewv = mm->ew_velocity;
int nsv = mm->ns_velocity;
double heading;
if ((mm->mesub == 1) || (mm->mesub == 2)) {
int ew_raw = ((msg[5] & 0x03) << 8) | msg[6];
int ew_vel = ew_raw - 1;
int ns_raw = ((msg[7] & 0x7F) << 3) | (msg[8] >> 5);
int ns_vel = ew_raw - 1;
if (mm->ew_dir) ewv *= -1;
if (mm->ns_dir) nsv *= -1;
heading = atan2(ewv,nsv);
if (mm->mesub == 2) { // If (supersonic) unit is 4 kts
ns_vel = ns_vel << 2;
ew_vel = ew_vel << 2;
}
// Convert to degrees
mm->heading = (int) (heading * 360 / (M_PI*2));
// We don't want negative values but a 0-360 scale
if (mm->heading < 0) mm->heading += 360;
} else {
mm->heading = 0;
if (ew_raw) { // Do East/West
mm->ew_velocity = ew_vel;
if (mm->ew_dir = ((msg[5] & 0x04) >> 2))
{ew_vel = 0 - ew_vel;}
}
if (ns_raw) { // Do North/South
mm->ns_velocity = ns_vel;
if (mm->ns_dir = ((msg[7] & 0x80) >> 7))
{ns_vel = 0 - ns_vel;}
}
if (ew_raw && ns_raw) {
// Compute velocity and angle from the two speed components
mm->velocity = (int) sqrt((ns_vel * ns_vel) + (ew_vel * ew_vel));
if (mm->velocity) {
mm->heading = (int) (atan2(ew_vel, ns_vel) * 180.0 / M_PI);
// We don't want negative values but a 0-360 scale
if (mm->heading < 0) mm->heading += 360;
}
}
} else if (mm->mesub == 3 || mm->mesub == 4) {
mm->heading_is_valid = msg[5] & (1<<2);
mm->heading = (int) (360.0/128) * (((msg[5] & 3) << 5) | (msg[6] >> 3));
int airspeed = ((msg[7] & 0x7f) << 3) | (msg[8] >> 5);
if (airspeed) {
--airspeed;
if (mm->mesub == 4) // If (supersonic) unit is 4 kts
{airspeed = airspeed << 2;}
mm->velocity = airspeed;
mm->tasflag = (msg[7] & 0x80);
}
if (mm->heading_is_valid = (msg[5] & 0x04)) {
mm->heading = ((((msg[5] & 0x03) << 8) | msg[6]) * 45) >> 7;
}
}
}
}
@ -1799,10 +1824,11 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
if (Modes.mode_ac)
{
int ModeA;
struct modesMessage mm;
int ModeA = detectModeA(pPreamble, &mm);
memset(&mm, 0, sizeof(mm));
if (ModeA) // We have found a valid ModeA/C in the data
if (ModeA = detectModeA(pPreamble, &mm)) // We have found a valid ModeA/C in the data
{
mm.timestampMsg = Modes.timestampBlk + ((j+1) * 6);
@ -1998,6 +2024,7 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
&& (sigStrength > MODES_MSG_SQUELCH_LEVEL)
&& (errors <= MODES_MSG_ENCODER_ERRS) ) {
struct modesMessage mm;
memset(&mm, 0, sizeof(mm));
// Set initial mm structure details
mm.timestampMsg = Modes.timestampBlk + (j*6);
@ -2998,6 +3025,7 @@ int decodeHexMessage(struct client *c) {
int l = strlen(hex), j;
unsigned char msg[MODES_LONG_MSG_BYTES];
struct modesMessage mm;
memset(&mm, 0, sizeof(mm));
// Always mark the timestamp as invalid for packets received over the internet
// Mixing of data from two or more different receivers and publishing