<?
function CalculateDist ( $lat1 , $lat2 , $lon1 , $lon2 ){
$a = 6378137 - 21 * sin ( lat );
$b = 6356752.3142 ;
$f = 1 / 298.257223563 ;
$p1_lat = $lat1 / 57.29577951 ;
$p2_lat = $lat2 / 57.29577951 ;
$p1_lon = $lon1 / 57.29577951 ;
$p2_lon = $lon2 / 57.29577951 ;
$L = $p2_lon - $p1_lon ;
$U1 = atan (( 1 - $f ) * tan ( $p1_lat ));
$U2 = atan (( 1 - $f ) * tan ( $p2_lat ));
$sinU1 = sin ( $U1 );
$cosU1 = cos ( $U1 );
$sinU2 = sin ( $U2 );
$cosU2 = cos ( $U2 );
$lambda = $L ;
$lambdaP = 2 * PI ;
$iterLimit = 20 ;
abs ( $lambda - $lambdaP ) > 1e-12 && $iterLimit > 0 ) {
$sinLambda = sin ( $lambda );
$cosLambda = cos ( $lambda );
$sinSigma = sqrt (( $cosU2 * $sinLambda ) * ( $cosU2 * $sinLambda ) + ( $cosU1 * $sinU2 - $sinU1 * $cosU2 * $cosLambda ) * ( $cosU1 * $sinU2 - $sinU1 * $cosU2 * $cosLambda ));
//if ($sinSigma==0){return 0;} // co-incident points
$cosSigma = $sinU1 * $sinU2 + $cosU1 * $cosU2 * $cosLambda ;
$sigma = atan2 ( $sinSigma , $cosSigma );
$alpha = asin ( $cosU1 * $cosU2 * $sinLambda / $sinSigma );
$cosSqAlpha = cos ( $alpha ) * cos ( $alpha );
$cos2SigmaM = $cosSigma - 2 * $sinU1 * $sinU2 / $cosSqAlpha ;
$C = $f / 16 * $cosSqAlpha *( 4 + $f *( 4 - 3 * $cosSqAlpha ));
$lambdaP = $lambda ;
$lambda = $L + ( 1 - $C ) * $f * sin ( $alpha ) * ( $sigma + $C * $sinSigma *( $cos2SigmaM + $C * $cosSigma *(- 1 + 2 * $cos2SigmaM * $cos2SigmaM )));
// if ($iterLimit==0) {
$uSq = $cosSqAlpha *( $a * $a - $b * $b )/( $b * $b );
$A = 1 + $uSq / 16384 *( 4096 + $uSq *(- 768 + $uSq *( 320 - 175 * $uSq )));
$B = $uSq / 1024 * ( 256 + $uSq *(- 128 + $uSq *( 74 - 47 * $uSq )));
$deltaSigma = $B * $sinSigma *( $cos2SigmaM + $B / 4 *( $cosSigma *(- 1 + 2 * $cos2SigmaM * $cos2SigmaM )- $B / 6 * $cos2SigmaM *(- 3 + 4 * $sinSigma * $sinSigma )*(- 3 + 4 * $cos2SigmaM * $cos2SigmaM )));
$s = $b * $A *( $sigma - $deltaSigma );
$s / 1000 ;
CalculateDist ( $lat1 , $lat2 , $lon1 , $lon2 );
?>
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John Doe wrote : 1882
There are a few problems with this, minor and major.
John Doe wrote : 1883
Oh I forgot to add, this obviously only calculates flat distance, not surface distance.
