Rotate coordinate systems to facilitate calculating azimuth and altitude angles.

RotateGlobe.js

function RotateGlobe(b, a, bradius, aradius)
{
    // Get modified coordinates of 'b' by rotating the globe so that 'a' is at lat=0, lon=0.
    var br = {lat:b.lat, lon:(b.lon - a.lon), elv:b.elv};
    var brp = LocationToPoint(br);

    // Rotate brp cartesian coordinates around the z-axis by a.lon degrees,
    // then around the y-axis by a.lat degrees.
    // Though we are decreasing by a.lat degrees, as seen above the y-axis,
    // this is a positive (counterclockwise) rotation (if B's longitude is east of A's).
    // However, from this point of view the x-axis is pointing left.
    // So we will look the other way making the x-axis pointing right, the z-axis
    // pointing up, and the rotation treated as negative.

    var alat = GeocentricLatitude(-a.lat * Math.PI / 180.0);
    var acos = Math.cos(alat);
    var asin = Math.sin(alat);

    var bx = (brp.x * acos) - (brp.z * asin);
    var by = brp.y;
    var bz = (brp.x * asin) + (brp.z * acos);

    return {x:bx, y:by, z:bz, radius:bradius};
}