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    <p>Here's a C implementation that I found, should be fairly straightforward to translate to PHP:</p> <pre><code>#define KmPerDegree 111.12000071117 #define DegreesPerKm (1.0/KmPerDegree) #define PI M_PI #define TwoPI (M_PI+M_PI) #define HalfPI M_PI_2 #define RadiansPerDegree (PI/180.0) #define DegreesPerRadian (180.0/PI) #define copysign(x,y) (((y)&lt;0.0)?-fabs(x):fabs(x)) #define NGT1(x) (fabs(x)&gt;1.0?copysign(1.0,x):(x)) #define ArcCos(x) (fabs(x)&gt;1?quiet_nan():acos(x)) #define hav(x) ((1.0-cos(x))*0.5) /* haversine */ #define ahav(x) (ArcCos(NGT1(1.0-((x)*2.0)))) /* arc haversine */ #define sec(x) (1.0/cos(x)) /* secant */ #define csc(x) (1.0/sin(x)) /* cosecant */ /* ** GreatCirclePos() -- ** ** Compute ending position from course and great-circle distance. ** ** Given a starting latitude (decimal), the initial great-circle ** course and a distance along the course track, compute the ending ** position (decimal latitude and longitude). ** This is the inverse function to GreatCircleDist). */ void GreatCirclePos(dist, course, slt, slg, xlt, xlg) double dist; /* -&gt; great-circle distance (km) */ double course; /* -&gt; initial great-circle course (degrees) */ double slt; /* -&gt; starting decimal latitude (-S) */ double slg; /* -&gt; starting decimal longitude(-W) */ double *xlt; /* &lt;- ending decimal latitude (-S) */ double *xlg; /* &lt;- ending decimal longitude(-W) */ { double c, d, dLo, L1, L2, coL1, coL2, l; if (dist &gt; KmPerDegree*180.0) { course -= 180.0; if (course &lt; 0.0) course += 360.0; dist = KmPerDegree*360.0-dist; } if (course &gt; 180.0) course -= 360.0; c = course*RadiansPerDegree; d = dist*DegreesPerKm*RadiansPerDegree; L1 = slt*RadiansPerDegree; slg *= RadiansPerDegree; coL1 = (90.0-slt)*RadiansPerDegree; coL2 = ahav(hav(c)/(sec(L1)*csc(d))+hav(d-coL1)); L2 = HalfPI-coL2; l = L2-L1; if ((dLo=(cos(L1)*cos(L2))) != 0.0) dLo = ahav((hav(d)-hav(l))/dLo); if (c &lt; 0.0) dLo = -dLo; slg += dLo; if (slg &lt; -PI) slg += TwoPI; else if (slg &gt; PI) slg -= TwoPI; *xlt = L2*DegreesPerRadian; *xlg = slg*DegreesPerRadian; } /* GreatCirclePos() */ </code></pre> <blockquote> <h3>Source: <a href="http://sam.ucsd.edu/sio210/propseawater/ppsw_c/gcdist.c" rel="noreferrer">http://sam.ucsd.edu/sio210/propseawater/ppsw_c/gcdist.c</a></h3> </blockquote>
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    1. COThanks very much, I converted this to PHP and it works perfectly. I will post the PHP code below.
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