Transform TWD97 to Latitude Longitude
<?php | |
function twd97_to_latlng($x, $y) { | |
$a = 6378137.0; | |
$b = 6356752.314245; | |
$lng0 = 121 * M_PI / 180; | |
$k0 = 0.9999; | |
$dx = 250000; | |
$dy = 0; | |
$e = pow((1 - pow($b, 2) / pow($a, 2)), 0.5); | |
$x -= $dx; | |
$y -= $dy; | |
$M = $y / $k0; | |
$mu = $M / ($a * (1.0 - pow($e, 2) / 4.0 - 3 * pow($e, 4) / 64.0 - 5 * pow($e, 6) / 256.0)); | |
$e1 = (1.0 - pow((1.0 - pow($e, 2)), 0.5)) / (1.0 + pow((1.0 - pow($e, 2)), 0.5)); | |
$J1 = (3 * $e1 / 2 - 27 * pow($e1, 3) / 32.0); | |
$J2 = (21 * pow($e1, 2) / 16 - 55 * pow($e1, 4) / 32.0); | |
$J3 = (151 * pow($e1, 3) / 96.0); | |
$J4 = (1097 * pow($e1, 4) / 512.0); | |
$fp = $mu + $J1 * sin(2 * $mu) + $J2 * sin(4 * $mu) + $J3 * sin(6 * $mu) + $J4 * sin(8 * $mu); | |
$e2 = pow(($e * $a / $b), 2); | |
$C1 = pow($e2 * cos($fp), 2); | |
$T1 = pow(tan($fp), 2); | |
$R1 = $a * (1 - pow($e, 2)) / pow((1 - pow($e, 2) * pow(sin($fp), 2)), (3.0 / 2.0)); | |
$N1 = $a / pow((1 - pow($e, 2) * pow(sin($fp), 2)), 0.5); | |
$D = $x / ($N1 * $k0); | |
$Q1 = $N1 * tan($fp) / $R1; | |
$Q2 = (pow($D, 2) / 2.0); | |
$Q3 = (5 + 3 * $T1 + 10 * $C1 - 4 * pow($C1, 2) - 9 * $e2) * pow($D, 4) / 24.0; | |
$Q4 = (61 + 90 * $T1 + 298 * $C1 + 45 * pow($T1, 2) - 3 * pow($C1, 2) - 252 * $e2) * pow($D, 6) / 720.0; | |
$lat = $fp - $Q1 * ($Q2 - $Q3 + $Q4); | |
$Q5 = $D; | |
$Q6 = (1 + 2 * $T1 + $C1) * pow($D, 3) / 6; | |
$Q7 = (5 - 2 * $C1 + 28 * $T1 - 3 * pow($C1, 2) + 8 * $e2 + 24 * pow($T1, 2)) * pow($D, 5) / 120.0; | |
$lng = $lng0 + ($Q5 - $Q6 + $Q7) / cos($fp); | |
$lat = ($lat * 180) / M_PI; | |
$lng = ($lng * 180) / M_PI; | |
return array( | |
'lat' => $lat, | |
'lng' => $lng | |
); | |
} | |
?> |
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http://blog.xuite.net/vexed/tech/53749528