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// taken from http://trac.osgeo.org/openlayers/wiki/GreatCircleAlgorithms
var EARTH_RADIUS = 3958.75;
var PI = 3.1415926535897932384626433832795;
var DEG2RAD = 0.01745329252;
var RAD2DEG = 57.29577951308;
function WGS84Distance(x1, y1, x2, y2) {
x1 = x1 * DEG2RAD;
y1 = y1 * DEG2RAD;
x2 = x2 * DEG2RAD;
y2 = y2 * DEG2RAD;
var a = sin(( y2-y1 ) / 2.0 )^2;
var b = sin(( x2-x1 ) / 2.0 )^2;
var c = sqrt( a + cos( y2 ) * cos( y1 ) * b );
return 2 * asin( c ) * EARTH_RADIUS;
}
function WGS84Bearing(x1, y1, x2, y2) {
x1 = x1 * DEG2RAD;
y1 = y1 * DEG2RAD;
x2 = x2 * DEG2RAD;
y2 = y2 * DEG2RAD;
var a = cos(y2) * sin(x2 - x1);
var b = cos(y1) * sin(y2) - sin(y1) * cos(y2) * cos(x2 - x1);
var adjust = 0;
if((a == 0) && (b == 0)) {
bearing = 0;
} else if( b == 0) {
if( a < 0)
bearing = 3 * PI / 2;
else
bearing = PI / 2;
} else if( b < 0)
adjust = PI;
else {
if( a < 0)
adjust = 2 * PI;
else
adjust = 0;
}
return (atan(a/b) + adjust) * RAD2DEG;
}
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