Best practices when sending GPS location data [HowTo]

Application Development
13

Just for future reference, here is the c code for packing the GPS data into 48 bits.

uint8_t coords[6]; // 6*8 bits = 48
int32_t lat = float_latitude * 10000;
int32_t lon = float_longitude * 10000;

// Pad 2 int32_t to 6 8uint_t, skipping the last byte (x >> 24)
coords[0] = lat;
coords[1] = lat >> 8;
coords[2] = lat >> 16;

coords[3] = lon;
coords[4] = lon >> 8;
coords[5] = lon >> 16;

LMIC_setTxData2(1, coords, sizeof(coords), 0);

And here is some example PHP-code to decode it back into floats:

// Unpack into 6 bytes      
$data = unpack('C*', $payload);

// Combine each 3 bytes into a 24bit int      
$lat = ($data[1] + ($data[2] << 8) + ($data[3] << 16)) / 10000;      
$lon = ($data[4] + ($data[5] << 8) + ($data[6] << 16)) / 10000;      
var_dump( $lat, $lon );
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