計算一個點是否在多邊形里 JavaScript實現

[JavaScript]代碼    

/** 
 * 計算一個點是否在多邊形里 
 * @param {Object} pt 標注點 
 * @param {Object} poly 多邊形數組 
 */  
function isInsidePolygon(pt, poly){  
    for (var c = false, i = -1, l = poly.length, j = l - 1; ++i < l; j = i)   
        ((poly[i].lat <= pt.lat && pt.lat < poly[j].lat) || (poly[j].lat <= pt.lat && pt.lat < poly[i].lat)) &&  
        (pt.lng < (poly[j].lng - poly[i].lng) * (pt.lat - poly[i].lat) / (poly[j].lat - poly[i].lat) + poly[i].lng) &&  
        (c = !c);  
    return c;  
}