/** * Convert this grid reference into a latitude and longitude * * @return */ function toLatLng() { $airy1830 = new RefEll(6377563.396, 6356256.909); $OSGB_F0 = 0.9996012717; $N0 = -100000.0; $E0 = 400000.0; $phi0 = deg2rad(49.0); $lambda0 = deg2rad(-2.0); $a = $airy1830->maj; $b = $airy1830->min; $eSquared = $airy1830->ecc; $phi = 0.0; $lambda = 0.0; $E = $this->easting; $N = $this->northing; $n = ($a - $b) / ($a + $b); $M = 0.0; $phiPrime = ($N - $N0) / ($a * $OSGB_F0) + $phi0; do { $M = $b * $OSGB_F0 * ((1 + $n + 5.0 / 4.0 * $n * $n + 5.0 / 4.0 * $n * $n * $n) * ($phiPrime - $phi0) - (3 * $n + 3 * $n * $n + 21.0 / 8.0 * $n * $n * $n) * sin($phiPrime - $phi0) * cos($phiPrime + $phi0) + (15.0 / 8.0 * $n * $n + 15.0 / 8.0 * $n * $n * $n) * sin(2.0 * ($phiPrime - $phi0)) * cos(2.0 * ($phiPrime + $phi0)) - 35.0 / 24.0 * $n * $n * $n * sin(3.0 * ($phiPrime - $phi0)) * cos(3.0 * ($phiPrime + $phi0))); $phiPrime += ($N - $N0 - $M) / ($a * $OSGB_F0); } while ($N - $N0 - $M >= 0.001); $v = $a * $OSGB_F0 * pow(1.0 - $eSquared * coordHelpers::sinSquared($phiPrime), -0.5); $rho = $a * $OSGB_F0 * (1.0 - $eSquared) * pow(1.0 - $eSquared * coordHelpers::sinSquared($phiPrime), -1.5); $etaSquared = $v / $rho - 1.0; $VII = tan($phiPrime) / (2 * $rho * $v); $VIII = tan($phiPrime) / (24.0 * $rho * pow($v, 3.0)) * (5.0 + 3.0 * coordHelpers::tanSquared($phiPrime) + $etaSquared - 9.0 * coordHelpers::tanSquared($phiPrime) * $etaSquared); $IX = tan($phiPrime) / (720.0 * $rho * pow($v, 5.0)) * (61.0 + 90.0 * coordHelpers::tanSquared($phiPrime) + 45.0 * coordHelpers::tanSquared($phiPrime) * coordHelpers::tanSquared($phiPrime)); $X = coordHelpers::sec($phiPrime) / $v; $XI = coordHelpers::sec($phiPrime) / (6.0 * $v * $v * $v) * ($v / $rho + 2 * coordHelpers::tanSquared($phiPrime)); $XII = coordHelpers::sec($phiPrime) / (120.0 * pow($v, 5.0)) * (5.0 + 28.0 * coordHelpers::tanSquared($phiPrime) + 24.0 * coordHelpers::tanSquared($phiPrime) * coordHelpers::tanSquared($phiPrime)); $XIIA = coordHelpers::sec($phiPrime) / (5040.0 * pow($v, 7.0)) * (61.0 + 662.0 * coordHelpers::tanSquared($phiPrime) + 1320.0 * coordHelpers::tanSquared($phiPrime) * coordHelpers::tanSquared($phiPrime) + 720.0 * coordHelpers::tanSquared($phiPrime) * coordHelpers::tanSquared($phiPrime) * coordHelpers::tanSquared($phiPrime)); $phi = $phiPrime - $VII * pow($E - $E0, 2.0) + $VIII * pow($E - $E0, 4.0) - $IX * pow($E - $E0, 6.0); $lambda = $lambda0 + $X * ($E - $E0) - $XI * pow($E - $E0, 3.0) + $XII * pow($E - $E0, 5.0) - $XIIA * pow($E - $E0, 7.0); return new LatLng(rad2deg($phi), rad2deg($lambda)); }