How to convert my binary (hex) data to latitude and longitude?

Question

I have some binary data stream which passes geo location coordinates - latitude and longitude. I need to find the method they are encoded.

4adac812 = 74°26.2         


        

Answer 1

Brainstorming here.

If we look at the lower 6 bits of the second byte (data[1]&0x3f) we get the "minutes" value for most of the examples.

0xda & 0x3f = 0x1a = 26; // ok
0x60 & 0x3f = 0; // ok
0xe8 & 0x3f = 0x28 = 40; // ok
0x3c & 0x3f = 0x3c = 60; // should be 56
0xfd & 0x3f = 0x3d = 61; // should be 59

Perhaps this is the right direction?

Answer 2

I have reordered your data so that we first have 3 longitures and then 3 latitudes:

74.438085, 74.438338, 74.669105, 43.004605, 42.938628, 42.993772

This is the best fit of the hexadecimals i can come up with is:

74.437368, 74.439881, 74.668392, 42.993224, 42.961388, 42.982391

The differences are: -0.000717, 0.001543, -0.000713, -0.011381, 0.022760, -0.011381

The program that generates these values from the complete Hex'es (4 not 3 bytes) is:

int main(int argc, char** argv) {
    int a[] = { 0x4adac812, 0x4adaee12, 0x4ae86d11, 0x2b6059f9, 0x2a3c8df9, 0x2afd0efb };
    int i = 0;
    while(i<3) {
        double b = (double)a[i] / (2<<(3*8)) * 8.668993 -250.0197;
        printf("%f\n",b);
        i++;
    }
    while(i<6) {
        double b = (double)a[i] / (2<<(3*8)) *  0.05586007 +41.78172;
        printf("%f\n",b);
    i++;
    }
    printf("press key");
    getch();
}

Answer 3

I have tried your new data packets:

74+40.1463/60 74+26.3003/60 74+26.2851/60 42+56.3177/60 43+0.2763/60 42+59.6263/60

74.66910, 74.43834, 74.43809, 42.93863, 43.00460, 42.99377

My program gives:

74.668392, 74.439881, 74.437368, 42.961388, 42.993224, 39.407346

The differences are:

-0.000708,  0.001541,  -0.000722,  0.022758, -0.011376, -3.586424

I re-used the 4 constants i derived from your first packet as those are probably stored in your client somewhere. The slight differences might be the result of some randomization the client does to prevent you from getting the exact value or reverse-engineering their protocol.