Calculating distance and speed using gps coordinates using qt c++ - c++

Question

I am attempting to convert the first code snippet at:
Calculate distance between 2 GPS coordinates
// var R = 6371; // km
// var dLat = (lat2-lat1).toRad();
// var dLon = (lon2-lon1).toRad();
// var lat1 = lat1.toRad();
// var lat2 = lat2.toRad();
// var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
// Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2);
// var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
// var d = R * c;
(also shown below) for use in qt c++. It is used in a program that simulates gps flight inside of a radio control simulator. The GpsCalcLoop grabs gps latitude and longitude (in decimal format) once per second. These are fed into my converted code in hopes of getting a distance traveled during that one second of time. Speed would then be calculated.
I used the information at this page:
http://doc.qt.io/qt-4.8/qtcore-qmath-h.html
to convert the math functions. The output, however, is not what I expected. No matter what is input into lat2, lat1, lon2, and lon1 the results are always the same, '16777200.00'.
I am hoping that someone more familiar with qt c++ will be able to show me where I have gone wrong with the conversion. or point me to where I can find qt c++ code that is working.
I will add that I have attempted to use "#include "<"QGeoPositionInfo">" but get a 'No such file or directory' error when running the program.
void TelemetrySimulator::onGpsCalcLoop()
{
if(rungps)
{
ui -> valuetest1 -> setValue(flat);
ui -> valuetest2 -> setValue(flat2);
ui -> valuetest3 -> setValue(flon);
ui -> valuetest4 -> setValue(flon2);
ui -> valuetest5 -> setValue(flat-flat2);
ui -> valuetest6 -> setValue(flon-flon2);
flat2 = flat;
flon2 = flon;
//--https://stackoverflow.com/questions/365826 //calculate-distance-between-2-gps-coordinates--
// var R = 6371; // km
// var dLat = (lat2-lat1).toRad();
// var dLon = (lon2-lon1).toRad();
// var lat1 = lat1.toRad();
// var lat2 = lat2.toRad();
// var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
// Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2);
// var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
// var d = R * c;
//--------------my conversio to qt c++---------
//---converted to qt using this web page -> http://doc.qt.io/qt-4.8/qtcore-qmath-h.html----
double R, dLat, dLon, lat1, lat2, lon2, lon1, a, c, d;
lat2 = flat2;
lat1 = flat;
lon2 = flon2;
lon1 = flon;
R = 6371; // km
dLat = qAcos(lat2-lat1); //dLat = (lat2-lat1).toRad(); instead of qAcos could be qAsin, qAtan, qCos, qSin,
// qTan. All refer to Radials.
dLon = qAcos(lon2-lon1); //dLon = (lon2-lon1).toRad();
lat1 = qAcos(lat1); //lat1 = lat1.toRad();
lat2 = qAcos(lat2); //lat2 = lat2.toRad();
a = qSin(dLat/2) * qSin(dLat/2) + //Math.sin(dLat/2) * Math.sin(dLat/2) +
qSin(dLon/2) * qSin(dLon/2) * qCos(lat1) * qCos(lat2);//Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2);
c = 2 * qAtan2(qSqrt(a), qSqrt(1-a)); //Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
d = R * c;
ui -> valuetest7 -> setValue(d);
}
}
Thanks to everyone for your great help! Here is the final code:
void MainWindow::onGpsCalcLoop()
{
//Get initial values from gps run loop-------
double lat2 = flat2;
double lat1 = flat;
double lon2 = flon2;
double lon1 = flon;
//GPS distance and speed calculation -------
double dLat = .01745329 * (lat2 - lat1);
double dLon = .01745329 * (lon2 - lon1);
lat1 = .01745329 * lat1;
lat2 = .01745329 * lat2;
double a = qSin(dLat/2) * qSin(dLat/2) +
qSin(dLon/2) * qSin(dLon/2) * qCos(lat1) * qCos(lat2);
double c = 2 * qAtan2(qSqrt(a), qSqrt(1-a));
double d = 3975 * c;
//Distance calculation done. Next is total distance and speed------
td = td + d;
if (d > .1)
{
d = 0;
td = 0;
}
if (ui -> metric -> isChecked())
{
ui -> valuetest1 -> setValue(td * 1.6);
ui -> valuetest2 -> setValue((d * 3600) * 1.6);
}
else
{
ui -> valuetest1 -> setValue(td);
ui -> valuetest2 -> setValue(d * 3600);
}
flat2 = flat;
flon2 = flon;
}
I used .01745329*(whatever) instead of qDegreesToRadians(whatever) just to keep things as simple as possible.
Again, thanks to all for your help!