Guys, I am asking for you help again. This time I am experiencing a problem when trying to calculate the distance between two locations(I have the latitude and longitude for each of the locations). I tried coding a simple MS-DOS program in C++, but I do not know how to make the appropriate conversions.Here is the sourcecode:double a1 = 450000; //first latitudedouble b1 = 230000; /first longitudedouble a2 = 455000; //second latitudedouble b2 = 230000; //second latitudedouble dist;double r = 3443.9; /radius of Earthcout << a1;cout << 'n';cout << b1;cout << 'n';cout << a2;cout << 'n';cout << b2;cout << 'n';/*a1 = a1 * pi / 180;b1 = b1 * pi / 180;b2 = b2 * pi / 180;*/dist = acos(cos(a1)*cos(b1)*cos(a2)*cos(b2) + cos(a1)*sin(b1)*cos(a2)*sin(b2) + sin(a1)*sin(a2)) * r;dist = dist * 180 / pi; My problem is that I do not get the appropriate answer(50.0895 nautical miles) I always get a different bigger answer. I used this website to help me out with determing the distance, and the sourcecode:http://jan.ucc.nau.edu/~cvm/latlongdist.html I also have a code that converts decimal degrees to deg:min:sec , but I do not know if I should use it. It is really not that important for me to use it, since I just want this code to work, and to correctly calculate the distance between these coordinates. I thank you very much for your help in advance. This really means a lot to me, and my project.Yours Truly,Tiberiu Brasov

I use this formula:...#include #ifndef PI #define PI 3.1415926535897932384626433832795 //circle number#endif#define HALFEARTH 10800 //half earth circumference in nautic miles#define RADIANS_TO_DEGREE_FACTOR (180.0/PI)#define DEG_SIN( val ) sin( ( val )/RADIANS_TO_DEGREE_FACTOR) //sinus in degrees#define DEG_COS( val ) cos( ( val )/RADIANS_TO_DEGREE_FACTOR) //cosine in degrees#define DEG_TAN( val ) tan( ( val )/RADIANS_TO_DEGREE_FACTOR) //tangens in degrees#define DEG_ASIN( val ) RADIANS_TO_DEGREE_FACTOR * asin(( val )) //arcsinus in degrees#define DEG_ACOS( val ) RADIANS_TO_DEGREE_FACTOR * acos(( val )) //arccosine in degrees#define DEG_ATAN( val ) RADIANS_TO_DEGREE_FACTOR * atan(( val )) //arctangens in degrees#define DEG_ATAN2( val1 , val2 ) RADIANS_TO_DEGREE_FACTOR * atan2( val1, val2 ) //atan2 in degrees#define RADIANS_TO_MINUTE_FACTOR (10800.0/PI)#define RADIANS_TO_MINUTE( val ) (RADIANS_TO_MINUTE_FACTOR *( val ))#define MIN_SIN( val ) (sin( ( val )/RADIANS_TO_MINUTE_FACTOR))#define MIN_COS( val ) (cos( ( val )/RADIANS_TO_MINUTE_FACTOR))#define MIN_TAN( val ) (tan( ( val )/RADIANS_TO_MINUTE_FACTOR))#define MIN_ASIN( val ) (RADIANS_TO_MINUTE_FACTOR * asin(( val )))#define MIN_ACOS( val ) (RADIANS_TO_MINUTE_FACTOR * acos(( val )))#define MIN_ATAN( val ) (RADIANS_TO_MINUTE_FACTOR * atan(( val )))#define MIN_ATAN2( val1 , val2 ) (RADIANS_TO_MINUTE_FACTOR * atan2( ( val1) , ( val2 ) ))/* #if (_MSC_VER >= 1300) && (WINVER < 0x0500) //VC7 or later, building with pre-VC7 runtime libraries extern "C" long _ftol( double ); //defined by VC6 C libs extern "C" long _ftol2( double dblSource ) { return _ftol( dblSource ); } #endif*///GREAT CIRCLE// _ // | // To| |InboundCourse// ---------------------------------------+----// | / | |// | / | / beta// | / -|- // | / .// | / .// | / .// | / .// DeltaTheta / Dist .// | / .// | / .// | / .// | alpha/ .// |-----/ .// | / .// |// .// -----+------------DeltaPhi---------->.// |From// |// |//double GrtCrcDist(double *pdblInboundCourse, double dblFromLat,double dblFromLong, double dblToLat,double dblToLong)// input (lat,lon) in degrees// output dist in minutes (==nm) course in degrees{ double dblDist=0,dblCourse=180,dblDeltaTheta=0,dblDeltaPhi=0; dblDeltaPhi=(dblToLong-dblFromLong)*0.5; dblDeltaTheta=(dblToLat-dblFromLat)*0.5; dblDist= DEG_SIN(dblDeltaTheta)*DEG_SIN(dblDeltaTheta)+ DEG_COS(dblFromLat)*DEG_COS(dblToLat)*DEG_SIN(dblDeltaPhi)*DEG_SIN(dblDeltaPhi); if(dblDist>0) { dblDist=sqrt(dblDist); if(dblDist<1) dblDist=2*MIN_ASIN(dblDist); else dblDist=HALFEARTH; dblCourse=DEG_ACOS( (DEG_SIN(dblFromLat)-DEG_SIN(dblToLat)*MIN_COS(dblDist))/ (DEG_COS(dblToLat)*MIN_SIN(dblDist)) ); } if(DEG_SIN(2.0*dblDeltaPhi)>0) dblCourse=360-dblCourse; if(pdblInboundCourse) *pdblInboundCourse=dblCourse; return dblDist;} ...it might be helpful. It does not use the cos-calculus of spheric triangles directly, but a little transformation to sin sin(x/2)=sqrt((1-cos(x))/2)this more accurate for short distances. Please remind the definition of nm, it is an arc minute. So only recalculate angles to minutes and you'll get nm.Arne Bartels

I use this for great circle:void NV_LLALLA2GC(PGPSLLA from, PGPSLLA to, PGPSRhumb r){ double d, c; double dlat, dlon, dlon2; dlon2 = (from->lon) - (to->lon); dlat = sin(((from->lat) - (to->lat)) * 0.5); dlon = sin( dlon2 * 0.5); d = 2.0 * asin(sqrt( (dlat * dlat) + (cos(from->lat) * cos(to->lat) * (dlon * dlon)) ) ); c = (atan2( sin(dlon2) * cos(to->lat) , cos(from->lat) * sin(to->lat) - sin(from->lat) * cos(to->lat) * cos(dlon) ) ); r->d = RAD2NM(d); r->tc = c;}all angles in Radians. r->d is distance and t->tc is true course, converted using:#define RAD2NM® ((double) (® * (3437.7467707849975) ) )Hope this helps!

Arne and Jean, Thank you very much for your help. I do not know what I would have done without you. I am still experiencing a problem while calculating the distance. I get the answer for both of the codes 2400. I use these values:From lat = 450000From long = 230000To lat = 455000To long = 230000 My questions are: What should I do to 2400 in order to get the distance between the latitudes in a nm format? Is 2400 considered as minutes, which need to be converted to nm? I am stuck, and any help is greatly appreciated.Sincerely,Tibeiru Brasov