c# - Calculate future latitude longitude with initial coordinates, heading and distance -

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i have been reading through stackoverflow , site (http://www.movable-type.co.uk/scripts/latlong.html) how this, cant code give correct answer. giving coordinate isnt in correct direction. have been working on day , seem have hit wall. function:

public static void destination() {      double heading = 335.9;      double startlatitude = 41.8369;      double startlongitude = 87.6847;       //convert radians      startlatitude = startlatitude * math.pi / 180;      startlongitude = startlongitude * math.pi / 180;      heading = heading * math.pi / 180;       int distancekilometers = 100;      double angulardistance = distancekilometers / 6371e3;       double endlat = math.asin((math.sin(startlatitude) * math.cos(angulardistance)) +                     (math.cos(startlatitude) * math.sin(angulardistance) * math.cos(heading)));      double endlong = startlongitude + (math.atan2((math.sin(heading) * math.sin(angulardistance) * math.cos(startlatitude)),                               math.cos((angulardistance) - (math.sin(startlatitude) * math.sin(endlat)))));       endlong = (endlong + 3 * math.pi) % (2 * math.pi) - math.pi;      console.writeline("endlatitude: " + (endlat * 180 / math.pi) + " endlongitude: " + (endlong * 180 / math.pi));   }

i use below function. float provide 3 meters precision. if need more, use double.

  internal class sxmath   {     internal const  float      pi                 = (float)math.pi;     internal const  float      x2pi               = pi * 2;     internal const  float      pidiv2             = pi/2;     internal const  float      radpersec          = (float)(pi / 648000f);     internal const  float      secperrad          = (float)(648000f / pi);     internal const  float      radperdeg          = pi / 180;     internal const  float      radpermin          = pi / 10800;     internal const  float      degperrad          = 180 / pi;     internal const  float      minparrad          = (float)(10800.0/pi);     internal const  float      radpermeter        = radpermin * (1f/1852f) /* meter_to_nms */ ;      internal static float realmod(float val,float modval)     { // example : realmod(3,2*pi)=3 , realmod(2*pi+3,2*pi)=3 , realmod(-3,2*pi)=2*pi-3        float result = (float)math.ieeeremainder(val,modval);       if (result<0) result = result + modval;       return result;     }   } // sxmath    internal struct sxgeopt   {     internal float lat ; // in radians, n positive     internal float lon ; // in radians, w positive   } // sxgeopt    internal static sxgeopt geo_coorpointinazim(sxgeopt p1,float az,float raddist)     // procedure provides coordinates of point p2 located     // - @ distance raddist of point p1     // - in direction of azimuth az     // input   p1        <sxgeopt> coordinates of reference point     //         raddist   <float>   distance in radian between p1 , p2     //         az        <float>   azimut of p2 p1,      //                             (az=0, if p1 , p2 on same longitude , p2 north of p1)     //                             (az=90, if p1 on equator , p2 on equtor @ east of p1)     // output  p2        <sxgeopt> coordinates of resulting point     {       sxgeopt result;       if (p1.lat>sxmath.pidiv2-sxmath.radpermin)       { if (az<=sxmath.pi) result.lon=az; else result.lon=az-sxmath.pi; result.lat=sxmath.pidiv2-raddist; }       else if (p1.lat<-sxmath.pidiv2+sxmath.radpermin)       { if (az<=sxmath.pi) result.lon=-az; else result.lon=-az+sxmath.pi; result.lat=-sxmath.pidiv2+raddist; }       else       {         result.lat = (float)math.asin((math.sin(p1.lat)*math.cos(raddist)) +                                    (math.cos(p1.lat)*math.sin(raddist)*math.cos(az)));         float dlon = (float)math.atan2( math.sin(az)*math.sin(raddist)*math.cos(p1.lat),                                          math.cos(raddist)-math.sin(p1.lat)*math.sin(result.lat));         result.lon = sxmath.realmod(p1.lon-dlon+sxmath.pi,sxmath.x2pi)-sxmath.pi;       }       return result;     }

as extracted code different classes, hope nothing missing.

to input parameter distinrad kilometers:

  float raddist = distancekilometers * 1000f * sxmath.radpermeter ;

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