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VK1ET : Only Decode valid AC12 and AC13 altitudes

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Decode DF17 altitudes only if valid (i.e. must be a non-zero field)
This commit is contained in:
Malcolm Robb 2013-05-08 20:13:11 +01:00
parent 8efe64982a
commit 6af4bb7431
1 changed files with 8 additions and 3 deletions
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11
dump1090.c
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@ -1230,7 +1230,6 @@ int decodeID13Field(int ID13Field) {
int decodeAC13Field(int AC13Field, int *unit) {
int m_bit = AC13Field & 0x0040; // set = meters, clear = feet
int q_bit = AC13Field & 0x0010; // set = 25 ft encoding, clear = Gillham Mode C encoding
AC13Field &= 0x1FFF; // limit the field to 13 bits
if (!m_bit) {
*unit = MODES_UNIT_FEET;
@ -1414,7 +1413,10 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
// Fields for DF0, DF4, DF16, DF20 13 bit altitude
if (mm->msgtype == 0 || mm->msgtype == 4 ||
mm->msgtype == 16 || mm->msgtype == 20) {
mm->altitude = decodeAC13Field(((msg[2] << 8) | msg[3]), &mm->unit);
int AC13Field = ((msg[2] << 8) | msg[3]) & 0x1FFF;
if (AC13Field) { // Only attempt to decode if a valid (non zero) altitude is present
mm->altitude = decodeAC13Field(AC13Field, &mm->unit);
}
}
// Fields for DF17 squitter
@ -1442,11 +1444,14 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
mm->flight[8] = '\0';
} else if (mm->metype >= 9 && mm->metype <= 18) { // Position Message
int AC12Field = ((msg[5] << 4) | (msg[6] >> 4)) & 0x0FFF;
mm->fflag = msg[6] & (1<<2);
mm->tflag = msg[6] & (1<<3);
mm->altitude = decodeAC12Field(((msg[5] << 4) | (msg[6] >> 4)), &mm->unit);
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]);
if (AC12Field) {// Only attempt to decode if a valid (non zero) altitude is present
mm->altitude = decodeAC12Field(AC12Field, &mm->unit);
}
} else if (mm->metype == 19) { // Airborne Velocity Message
if (mm->mesub == 1 || mm->mesub == 2) {