如何在谷歌地图中计算矩形区域？

Question

我正在学习C＃，google map api。我想绘制点击矩形并计算矩形区域。 这是我的代码：

function mode() {
   google.maps.event.addListener(map, 'click', function (event) {
        var bounds = makeBounds(event.latLng, 200, 100);

        placeRec(bounds);
    });
}

function placeRec(bounds) {
    var rectangle = new google.maps.Rectangle({
        strokeColor: '#FF0000',
        strokeOpacity: 0.8,
        strokeWeight: 2,
        fillColor: '#FF0000',
        fillOpacity: 0.35,
        map: map,
        editable: true,
        bounds: bounds,
        draggable:true
    });
}


function makeBounds(nw, metersEast, metersSouth) {
    ne = google.maps.geometry.spherical.computeOffset(nw, metersEast, 90);
    sw = google.maps.geometry.spherical.computeOffset(nw, metersSouth, 180);
    return new google.maps.LatLngBounds(sw, ne);
    sowe = bounds.getSouthWest();
    noea = bounds.getNorthEast();
}

我在谷歌地图中成功绘制了点击矩形， 我想知道计算矩形区域。

我该怎么办？

谢谢