Calculation of two point distance from location sensor

Calculation of two point distance from location sensor.

Unit of result value is a km.

function TForm1.CalcDistance( lon1, lat1,  lon2, lat2 : single ) : single; var    theta, dist : double;   begin    theta := lon1 - lon2;    dist := sin( degTorad(lat1)) * sin(degTorad(lat2)) + cos(degTorad(lat1)) * cos(degTorad(lat2)) * cos(degTorad(theta));    dist := arccos(dist);    dist := radTodeg(dist);    dist := dist * 60 * 1.1515;    dist := dist * 1.609344;    result := dist; end;