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ADSB position decoding

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Date and time string format function
Binary update
This commit is contained in:
furrtek 2017-08-17 12:56:47 +01:00
parent 9d902bc224
commit 2628f9c03d
15 changed files with 255 additions and 108 deletions
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105
firmware/common/adsb.cpp
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@ -138,11 +138,11 @@ void encode_frame_squawk(ADSBFrame& frame, const uint32_t squawk) {
}
float cpr_mod(float a, float b) {
return a - (b * floor(a / b));
return a - (b * floor(a / b));
}
int cpr_NL(float lat) {
if (lat < 0)
if (lat < 0)
lat = -lat; // Symmetry
for (size_t c = 0; c < 58; c++) {
@ -150,7 +150,7 @@ int cpr_NL(float lat) {
return 59 - c;
}
return 1;
return 1;
}
int cpr_N(float lat, int is_odd) {
@ -162,6 +162,10 @@ int cpr_N(float lat, int is_odd) {
return nl;
}
float cpr_Dlon(float lat, int is_odd) {
return 360.0 / cpr_N(lat, is_odd);
}
void encode_frame_pos(ADSBFrame& frame, const uint32_t ICAO_address, const int32_t altitude,
const float latitude, const float longitude, const uint32_t time_parity) {
@ -203,35 +207,76 @@ void encode_frame_pos(ADSBFrame& frame, const uint32_t ICAO_address, const int32
frame.make_CRC();
}
// Decoding method (from dump1090):
// index int j = floor(((59 * latcprE - 60 * latcprO) / 131072) + 0.50)
// latE = DlatE * (cpr_mod(j, 60) + (latcprE / 131072))
// latO = DlatO * (cpr_mod(j, 59) + (latcprO / 131072))
// if latE >= 270 -> latE -= 360
// if latO >= 270 -> latO -= 360
// if (cpr_NL(latE) != cpr_NL(latO)) return;
// int ni = cpr_N(latE ,0);
// int m = floor((((loncprE * (cpr_NL(latE) - 1)) - (loncprO * cpr_NL(latE))) / 131072) + 0.5)
// lon = cpr_Dlon(latE, 0) * (cpr_mod(m, ni) + loncprE / 131072);
// lat = latE;
// ... or ...
// int ni = cpr_N(latO ,0);
// int m = floor((((loncprE * (cpr_NL(latO) - 1)) - (loncprO * cpr_NL(latO))) / 131072) + 0.5)
// lon = cpr_Dlon(latO, 0) * (cpr_mod(m, ni) + loncprO / 131072);
// lat = latO;
// ... and ...
// if (lon > 180) lon -= 360;
// Only altitude is decoded for now
uint32_t decode_frame_pos(ADSBFrame& frame) {
uint8_t * raw_data = frame.get_raw_data();
// Decoding method from dump1090
adsb_pos decode_frame_pos(ADSBFrame& frame_even, ADSBFrame& frame_odd) {
uint8_t * raw_data;
uint32_t latcprE, latcprO, loncprE, loncprO;
float latE, latO, m, Dlon;
int ni;
adsb_pos position { false, 0, 0, 0 };
// Q-bit is present
if (raw_data[5] & 1)
return ((((raw_data[5] >> 1) << 4) | ((raw_data[6] & 0xF0) >> 4)) * 25) - 1000;
uint32_t time_even = frame_even.get_rx_timestamp();
uint32_t time_odd = frame_odd.get_rx_timestamp();
uint8_t * frame_data_even = frame_even.get_raw_data();
uint8_t * frame_data_odd = frame_odd.get_raw_data();
return 0;
// Return most recent altitude
if (time_even > time_odd)
raw_data = frame_data_even;
else
raw_data = frame_data_odd;
// Q-bit must be present
if (raw_data[5] & 1)
position.altitude = ((((raw_data[5] & 0xFE) << 3) | ((raw_data[6] & 0xF0) >> 4)) * 25) - 1000;
// Position
latcprE = ((frame_data_even[6] & 3) << 15) | (frame_data_even[7] << 7) | (frame_data_even[8] >> 1);
loncprE = ((frame_data_even[8] & 1) << 16) | (frame_data_even[9] << 8) | frame_data_even[10];
latcprO = ((frame_data_odd[6] & 3) << 15) | (frame_data_odd[7] << 7) | (frame_data_odd[8] >> 1);
loncprO = ((frame_data_odd[8] & 1) << 16) | (frame_data_odd[9] << 8) | frame_data_odd[10];
// Compute latitude index
float j = floor((((59.0 * latcprE) - (60.0 * latcprO)) / 131072.0) + 0.5);
latE = (360.0 / 60.0) * (cpr_mod(j, 60) + (latcprE / 131072.0));
latO = (360.0 / 59.0) * (cpr_mod(j, 59) + (latcprO / 131072.0));
if (latE >= 270) latE -= 360;
if (latO >= 270) latO -= 360;
// Both frames must be in the same latitude zone
if (cpr_NL(latE) != cpr_NL(latO))
return position;
// Compute longitude
if (time_even > time_odd) {
// Use even frame
ni = cpr_N(latE, 0);
Dlon = 360.0 / ni;
m = floor((((loncprE * (cpr_NL(latE) - 1)) - (loncprO * cpr_NL(latE))) / 131072.0) + 0.5);
position.longitude = Dlon * (cpr_mod(m, ni) + loncprE / 131072.0);
position.latitude = latE;
} else {
// Use odd frame
ni = cpr_N(latO, 1);
Dlon = 360.0 / ni;
m = floor((((loncprE * (cpr_NL(latO) - 1)) - (loncprO * cpr_NL(latO))) / 131072.0) + 0.5);
position.longitude = Dlon * (cpr_mod(m, ni) + loncprO / 131072.0);
position.latitude = latO;
}
if (position.longitude > 180) position.longitude -= 360;
position.valid = true;
return position;
}
// speed is in knots