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copied!<p>I needed the same function, and javascript made it difficult to interact with the DB. I have converted your JS to PHP and this could be more useful when updating your database - ie: query table, loop through result set, call function, update table.</p> <pre><code>function OSGridToLatLong($E, $N) { $a = 6377563.396; $b = 6356256.910; // Airy 1830 major & minor semi-axes $F0 = 0.9996012717; // NatGrid scale factor on central meridian $lat0 = 49*M_PI/180; $lon0 = -2*M_PI/180; // NatGrid true origin $N0 = -100000; $E0 = 400000; // northing & easting of true origin, metres $e2 = 1 - ($b*$b)/($a*$a); // eccentricity squared $n = ($a-$b)/($a+$b); $n2 = $n*$n; $n3 = $n*$n*$n; $lat=$lat0; $M=0; do { $lat = ($N-$N0-$M)/($a*$F0) + $lat; $Ma = (1 + $n + (5/4)*$n2 + (5/4)*$n3) * ($lat-$lat0); $Mb = (3*$n + 3*$n*$n + (21/8)*$n3) * sin($lat-$lat0) * cos($lat+$lat0); $Mc = ((15/8)*$n2 + (15/8)*$n3) * sin(2*($lat-$lat0)) * cos(2*($lat+$lat0)); $Md = (35/24)*$n3 * sin(3*($lat-$lat0)) * cos(3*($lat+$lat0)); $M = $b * $F0 * ($Ma - $Mb + $Mc - $Md); // meridional arc } while ($N-$N0-$M >= 0.00001); // ie until < 0.01mm $cosLat = cos($lat); $sinLat = sin($lat); $nu = $a*$F0/sqrt(1-$e2*$sinLat*$sinLat); // transverse radius of curvature $rho = $a*$F0*(1-$e2)/pow(1-$e2*$sinLat*$sinLat, 1.5); // meridional radius of curvature $eta2 = $nu/$rho-1; $tanLat = tan($lat); $tan2lat = $tanLat*$tanLat; $tan4lat = $tan2lat*$tan2lat; $tan6lat = $tan4lat*$tan2lat; $secLat = 1/$cosLat; $nu3 = $nu*$nu*$nu; $nu5 = $nu3*$nu*$nu; $nu7 = $nu5*$nu*$nu; $VII = $tanLat/(2*$rho*$nu); $VIII = $tanLat/(24*$rho*$nu3)*(5+3*$tan2lat+$eta2-9*$tan2lat*$eta2); $IX = $tanLat/(720*$rho*$nu5)*(61+90*$tan2lat+45*$tan4lat); $X = $secLat/$nu; $XI = $secLat/(6*$nu3)*($nu/$rho+2*$tan2lat); $XII = $secLat/(120*$nu5)*(5+28*$tan2lat+24*$tan4lat); $XIIA = $secLat/(5040*$nu7)*(61+662*$tan2lat+1320*$tan4lat+720*$tan6lat); $dE = ($E-$E0); $dE2 = $dE*$dE; $dE3 = $dE2*$dE; $dE4 = $dE2*$dE2; $dE5 = $dE3*$dE2; $dE6 = $dE4*$dE2; $dE7 = $dE5*$dE2; $lat = $lat - $VII*$dE2 + $VIII*$dE4 - $IX*$dE6; $lon = $lon0 + $X*$dE - $XI*$dE3 + $XII*$dE5 - $XIIA*$dE7; return array( 'longitude' => $lon * 180 / M_PI, 'latitude' => $lat * 180 / M_PI ); } </code></pre>

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