cesium 拾取模型表面的坐標

scene = viewer.scene;
var handler = new Cesium.ScreenSpaceEventHandler(scene.canvas);
handler.setInputAction(function(evt) {
    var scene = viewer.scene;
    if (scene.mode !== Cesium.SceneMode.MORPHING) {
        var pickedObject = scene.pick(evt.position);
        if (scene.pickPositionSupported && Cesium.defined(pickedObject)) {
            var cartesian = viewer.scene.pickPosition(evt.position);
            if (Cesium.defined(cartesian)) {
                var cartographic = Cesium.Cartographic.fromCartesian(cartesian);
                var lng = Cesium.Math.toDegrees(cartographic.longitude);
                var lat = Cesium.Math.toDegrees(cartographic.latitude);
                var height = cartographic.height;//模型高度
                mapPosition={x:lng,y:lat,z:height};
                console.log(mapPosition);
            }
        }
    }
}, Cesium.ScreenSpaceEventType.LEFT_CLICK);