CODEWITHSUNDEEP
c#gps
Fabricio Rodriguez
Fabricio Rodriguez

Reputation: 4239

Decoding 4 byte latitude/4 byet longitude of Concox TR06 GPS tracker

We have a Concox TG06 GPS tracker. I am receiving data from it via TCP, but I am struggling to decode the latitude and longitude coordinates (in C#). According to the protocol manual, the message from the tracker (terminal) to the server looks like this:

Concox TR06 position protocol

As you can see, the latitude and longitude coordinates are 4 bytes each. Further down, the manual explains how these coordinates are formatted:

5.2.1.6 Latitude Four bytes are consumes, defining the latitude value of location data. The range of the value is 0 - 162000000, indicating a range of 0°-90°. The conversion method thereof is as follow: Converting the value of latitude and longitude output by GPS module into a decimal based on minute; multiplying the converted decimal by 30000; and converting the multiplied result into hexadecimal. Example: 22º32.7658’=(22X60+32.7658)X30000=40582974, then converted into a hexadecimal number 40582974(Decimal)= 26B3F3E(Hexadecimal) at last the value is 0x02 0x6B 0x3F 0x3E

I am REALLY struggling to work this out backwards - i.e. getting from the four bytes (0x02 0x6B 0x3F 0x3E) to the latitude coordinate (not necessarily in degrees and minutes, as I use decimal degrees in my code). Basically I am trying to create a function whose shell looks like this:

private double DecodeLat(byte[] latBytes)
{
    double latitude;
    // implementation
    return latitude;
{

(And obviously same for longitude). I would greatly appreciate any help at all!

Thank you

Upvotes: 2

Views: 3148

Answers (4)

William Mutua Peter
William Mutua Peter

Reputation: 419

Take for instance converting the Hex Latitude 0x027AC7EB to degrees.

You can do conversion in 4 steps:

  1. Convert the Hex Lat value to Decimal: 0x027AC7EB => 41601003

  2. Divide the value you get by 30000: 41601003 / 30000 => 1,386.7001

  3. Divide by 60 to convert the value to degrees: 1,386.7001 / 60 => 23.11166833333333 degrees

  4. Prefix the minus or plus depending on the hemisphere.

    How it works?

    For Latitude: - North prefix + - South prefix -

    For Longitude: - East prefix + - West prefix -

    You can extract these positioning values from the Course and Status Bytes

eg. if decoding the course and status byte evaluates to a South Latitude, the final Latitude value would be -23.11166833333333 degrees

Same process applies for decoding the Longitude.

Upvotes: 0

shal
shal

Reputation: 171

For concox protocol the conversion of binary data is pretty straightforward - you just scan 4 binary bytes into number (little endian - e.g. just simple conversion to 32-bit unsigned integer) and then divide this number by 1800000.0. The result is in decimal degrees. Southern and Western hemispheres are defined by the sign, and sign is located in special bit of byte followed by the coordinates.

If you will have troubles with further data parsing from the device take a look at specialized cloud services that provide full protocol parsing and output completed parsed JSON message, like this.

Disclaimer: I'm related to flespi parsing backend and my opinion can be influenced by this product.

Upvotes: 0

Pepernoot
Pepernoot

Reputation: 3609

The longitude is 4 bytes because I can not see implementation I assume you try to read the double with 

BitConverter.ToDouble(Buffer, index);

a double = 8 bytes

if this is not the case Let me know in the comment, please

Upvotes: 1

Phylogenesis
Phylogenesis

Reputation: 7880

You can decode it as follows:

public static decimal DecodeLatitude(byte[] bytes)
{
    decimal minutes = (bytes[0] << 24) + (bytes[1] << 16) + (bytes[2] << 8) + bytes[3];
    minutes /= 30000;

    return minutes;
}

See an example here.

Upvotes: 2

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