Chris Nolan [http://chrisnolan.ca/] has help to light a fire under my
ass about this outstanding math equation. Are there an math/geo gurus
out there who can help me to get this working?
Here is a sample PHP page that attempts to display the distance
between Seattle and New York (given only their lat/lon values).
According to this, I'm getting 3869 miles between the two cities, but
my road atlas says only 2816 miles.
// GET VARIABLES
$unit = $_REQUEST['unit'];
// EARTH RADIUS
$radius_mi = 3443.9;
$radius_km = 6378;
// VALUE OF PI
$pi = 3.14159265;
// UNITS OF MEASUREMENT
if ($unit = "km") {
$r = $radius_km;
} else {
$r = $radius_mi;
}
// SEATTLE LAT&LON
$a1 = 47.6125;
$b1 = -122.328;
// NEW YORK LAT&LON
$a2 = 40.714;
$b2 = -74.007;
// COMMENTS STOP HERE
// BECAUSE I'M LOST
$a1 = abs($a1) * ($pi/180);
$b1 = abs($b1) * ($pi/180);
$a2 = abs($a2) * ($pi/180);
$b2 = abs($b2) * ($pi/180);
$distance = acos(cos($a1)*cos($b1)*cos($a2)*cos($b2) +
cos($a1)*sin($b1)*cos($a2)*sin($b2) + sin($a1)*sin($a2)) * $r;
echo $distance . "<br />\n";
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