Converting GPS coordinates to Cartesian coordinates and normal vector.

LocationToPoint.js

function LocationToPoint(c)
{
    // Convert (lat, lon, elv) to (x, y, z).
    var lat = c.lat * Math.PI / 180.0;
    var lon = c.lon * Math.PI / 180.0;
    var radius = EarthRadiusInMeters(lat);
    var clat   = GeocentricLatitude(lat);

    var cosLon = Math.cos(lon);
    var sinLon = Math.sin(lon);
    var cosLat = Math.cos(clat);
    var sinLat = Math.sin(clat);
    var x = radius * cosLon * cosLat;
    var y = radius * sinLon * cosLat;
    var z = radius * sinLat;

    // We used geocentric latitude to calculate (x,y,z) on the Earth's ellipsoid.
    // Now we use geodetic latitude to calculate normal vector from the surface, to correct for elevation.
    var cosGlat = Math.cos(lat);
    var sinGlat = Math.sin(lat);

    var nx = cosGlat * cosLon;
    var ny = cosGlat * sinLon;
    var nz = sinGlat;

    x += c.elv * nx;
    y += c.elv * ny;
    z += c.elv * nz;

    return {x:x, y:y, z:z, radius:radius, nx:nx, ny:ny, nz:nz};
}