Question

I have a GPS device which sends data to my server, I need to convert the decimal values that the device sends into latitude and longitude. I am bad at math so all my attempts failed, here are the specs:

Latitude

Occupy 4 bytes, representing the latitude value.

Number range is from 0 to 162000000, which represents the range form 0°to 90°.
Unit: 1/500 second Conversion method:

A) Convert the latitude (degrees, minutes) data from GPS module into a new form which represents the value only in minutes;

B Multiply the converted value by 30000, and then transform the result to hexadecimal number

For example22°32.7658′,（22×60＋32.7658）×30000=40582974, then convert it to hexadecimal number 0x02 0x6B 0x3F 0x3E

Longitude

Occupy 4 bytes, representing the longitude value of location data. Number ranges from 0 to 324000000, representing the range form 0°to 180°.Unit: 1/500 seconds, Conversion method is the same as latitude’s.

I came up with this function but it doesn’t seem to work:

procedure GetDegree(const numar : DWORD; out min,sec : Extended);
var
  eu : Extended;
begin
  eu :=  numar / 30000;
  min := Trunc(eu / 60);
  sec := eu - min * 60;
end;

Answer 1

numar is specified in 1/500th of a second. So, the following equations hold:

num/500 = seconds
num/500/60 = minutes
num/500/60/60 = degrees

I would calculate it all like this:

var
  degrees, minutes, seconds: Integer;
....
  degrees := num div (500*60*60);
  minutes := num div (500*60) - degrees*60;
  seconds := num div 500 - minutes*60 - degrees*60*60;

If you need to calculate the fractional part of seconds then do it like this. Note that there’s simply no need for Extended here.

var
  degrees, minutes: Integer;
  seconds: Double;
....
  degrees := num div (500*60*60);
  minutes := num div (500*60) - degrees*60;
  seconds := num/500 - minutes*60 - degrees*60*60;

Plug your value of 40582974 into these formula and the results are:

degrees: 22
minutes: 32
seconds: 45

Judging from comments what you actually want is degrees as an integer and minutes as a floating point. That you can do like this:

var
  degrees: Integer;
  minutes: Double;
....
  degrees := num div (500*60*60);
  minutes := num/(500*60) - degrees*60;

Plug your value of 40582974 into these formula and the results are:

degrees: 22
minutes: 32.7658