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VK1ET ; Decode DF-17 ground position reports

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Malcolm Robb 2013-05-09 00:40:57 +01:00
parent 6b53c9e73a
commit 5f009a3264
1 changed files with 34 additions and 4 deletions
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dump1090.c
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@ -1278,6 +1278,25 @@ int decodeAC12Field(int AC12Field, int *unit) {
return (100 * n); return (100 * n);
} }
} }
//
// Decode the 7 bit ground movement field PWL exponential style scale
//
int decodeMovementField(int movement) {
int gspeed;
// Note : movement codes 0,125,126,127 are all invalid, but they are
// trapped for before this function is called.
if (movement > 123) gspeed = 199; // > 175kt
else if (movement > 108) gspeed = ((movement - 108) * 5) + 100;
else if (movement > 93) gspeed = ((movement - 93) * 2) + 70;
else if (movement > 38) gspeed = ((movement - 38) ) + 15;
else if (movement > 12) gspeed = ((movement - 11) >> 1) + 2;
else if (movement > 8) gspeed = ((movement - 6) >> 2) + 1;
else gspeed = 0;
return (gspeed);
}
/* Capability table. */ /* Capability table. */
char *ca_str[8] = { char *ca_str[8] = {
@ -1445,14 +1464,25 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
mm->flight[8] = '\0'; mm->flight[8] = '\0';
} else if (mm->metype >= 9 && mm->metype <= 18) { // Position Message } else if (mm->metype >= 5 && mm->metype <= 18) { // Position Message
int AC12Field = ((msg[5] << 4) | (msg[6] >> 4)) & 0x0FFF;
mm->fflag = msg[6] & (1<<2); mm->fflag = msg[6] & (1<<2);
mm->tflag = msg[6] & (1<<3); mm->tflag = msg[6] & (1<<3);
mm->raw_latitude = ((msg[6] & 3) << 15) | (msg[7] << 7) | (msg[8] >> 1); mm->raw_latitude = ((msg[6] & 3) << 15) | (msg[7] << 7) | (msg[8] >> 1);
mm->raw_longitude = ((msg[8] & 1) << 16) | (msg[9] << 8) | (msg[10]); mm->raw_longitude = ((msg[8] & 1) << 16) | (msg[9] << 8) | (msg[10]);
if (mm->metype >= 9) { // Airborne
int AC12Field = ((msg[5] << 4) | (msg[6] >> 4)) & 0x0FFF;
if (AC12Field) {// Only attempt to decode if a valid (non zero) altitude is present if (AC12Field) {// Only attempt to decode if a valid (non zero) altitude is present
mm->altitude = decodeAC12Field(AC12Field, &mm->unit); {mm->altitude = decodeAC12Field(AC12Field, &mm->unit);}
}
} else { // Ground
int movement = ((msg[4] << 4) | (msg[5] >> 4)) & 0x007F;
if ((movement) && (movement < 125))
{mm->velocity = decodeMovementField(movement);}
mm->heading_is_valid = (msg[5] & 0x08);
if (mm->heading_is_valid) {
mm->heading = ((((msg[5] << 4) | (msg[6] >> 4)) & 0x007F) * 45) >> 4;
}
} }
} else if (mm->metype == 19) { // Airborne Velocity Message } else if (mm->metype == 19) { // Airborne Velocity Message