这是一个非常有用的距离计算函数，利用纬度和经度计算从 A 地点到 B 地点的距离。该函数可以返回英里，公里，海里三种单位类型的距离。

function distance($lat1, $lon1, $lat2, $lon2, $unit) { 

$theta = $lon1 - $lon2; 
$dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta)); 
$dist = acos($dist); 
$dist = rad2deg($dist); 
$miles = $dist * 60 * 1.1515; 
$unit = strtoupper($unit); 

if ($unit == "K") { 
return ($miles * 1.609344); 
} else if ($unit == "N") { 
return ($miles * 0.8684); 
} else { 
return $miles; 
} 
} 

//用法：
echo distance(32.9697, -96.80322, 29.46786, -98.53506, "k")." kilometers";