LBS——地理围栏(JS)

/*
 围栏计算
 */
var GPS_EleFence = {
    IsPtInPoly: function (ALon, ALat, APoints) {
        var iSum = 0,
            iCount;
        var dLon1, dLon2, dLat1, dLat2, dLon;
        if (APoints.length < 3) return false;
        iCount = APoints.length;
        for (var i = 0; i < iCount; i++) {
            if (i == iCount) {
                dLon1 = APoints[i].lng;
                dLat1 = APoints[i].lat;
                dLon2 = APoints[0].lng;
                dLat2 = APoints[0].lat;
            } else {
                dLon1 = APoints[i].lng;
                dLat1 = APoints[i].lat;
                dLon2 = APoints[i + 1].lng;
                dLat2 = APoints[i + 1].lat;
            }
            //以下语句判断A点是否在边的两端点的水平平行线之间，在则可能有交点，开始判断交点是否在左射线上
            if (((ALat >= dLat1) && (ALat < dLat2)) || ((ALat >= dLat2) && (ALat < dLat1))) {
                if (Math.abs(dLat1 - dLat2) > 0) {
                    //得到 A点向左射线与边的交点的x坐标：
                    dLon = dLon1 - ((dLon1 - dLon2) * (dLat1 - ALat)) / (dLat1 - dLat2);
                    if (dLon < ALon)
                        iSum++;
                }
            }
        }
        if (iSum % 2 != 0)
            return true;
        return false;
    }
};