JavaScript-GIS工具代碼

 JavaScript中計算方位角/投影距離/目標點算法：

let GeoUtil = (() => {
    let toRadian = Math.PI / 180.0;
    let radius_km = 6371;

    /**
     * Returns the distance from this point to the supplied point, in km
     * (using Haversine formula)
     *
     * from: Haversine formula - R. W. Sinnott, "Virtues of the Haversine",
     *       Sky and Telescope, vol 68, no 2, 1984
     *
     * @param   {LatLon} start: Latitude/longitude of destination point
     * @param   {Number} [precision=4]: no of significant digits to use for returned value
     * @returns {Number} Distance in km between this point and destination point
     */
    function distance(start, end) {

        var R = radius_km;
        var lat1 = start[0] * toRadian, lon1 = start[1] * toRadian;
        var lat2 = end[0] * toRadian, lon2 = end[1] * toRadian;
        var dLat = lat2 - lat1;
        var dLon = lon2 - lon1;

        var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
            Math.cos(lat1) * Math.cos(lat2) *
            Math.sin(dLon / 2) * Math.sin(dLon / 2);
        var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
        var d = R * c;
        return d;
    }

    /**
     * Returns the (initial) bearing from this point to the supplied point, in degrees
     *   see http://williams.best.vwh.net/avform.htm#Crs
     *
     * @param   {LatLon} point: Latitude/longitude of destination point
     * @returns {Number} Initial bearing in degrees from North
     */



    function bearing(start, end) {
        var lat1 = start[0] * toRadian, lat2 = end[0] * toRadian;
        var dLon = (end[1] - start[1]) * toRadian;

        var y = Math.sin(dLon) * Math.cos(lat2);
        var x = Math.cos(lat1) * Math.sin(lat2) -
            Math.sin(lat1) * Math.cos(lat2) * Math.cos(dLon);
        var brng = Math.atan2(y, x) / toRadian;

        return (brng + 360) % 360;
    }

    /**
     * Returns the destination point from this point having travelled the given distance (in km) on the
     * given initial bearing (bearing may vary before destination is reached)
     *
     *   see http://williams.best.vwh.net/avform.htm#LL
     *
     * @param   {Number} brng: Initial bearing in degrees
     * @param   {Number} dist: Distance in km
     * @returns {LatLon} Destination point
     */
    function destination(start, brng, dist) {
        dist = dist / 6371;  // convert dist to angular distance in radians
        brng = brng * toRadian;  //
        var lat1 = start[0] * toRadian, lon1 = start[1] * toRadian;

        var lat2 = Math.asin(Math.sin(lat1) * Math.cos(dist) +
            Math.cos(lat1) * Math.sin(dist) * Math.cos(brng));
        var lng2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(dist) * Math.cos(lat1),
            Math.cos(dist) - Math.sin(lat1) * Math.sin(lat2));
        lng2 = (lng2 + 3 * Math.PI) % (2 * Math.PI) - Math.PI;  // normalise to -180...+180

        return [lat2 / toRadian, lng2 / toRadian];
    }

    return {
        distance: distance,
        bearing: bearing,
        destination: destination
    };

})();