Cesium之【空间面积】测量

空间面积测量对象是平面，考虑到了取点的高度；地表面积测量的是球体（地球）曲面 

//****************************测量空间面积************************************************//
var measureAreaSpace = function (viewer, handler){	
	handler = new Cesium.ScreenSpaceEventHandler(viewer.scene._imageryLayerCollection);
	var positions = [];
	var tempPoints = [];
	var polygon = null;
	var tooltip = document.getElementById("toolTip");
	var cartesian = null;
	var floatingPoint;//浮动点
	tooltip.style.display = "block";
	
	handler.setInputAction(function(movement){
		tooltip.style.left = movement.endPosition.x + 3 + "px";
		tooltip.style.top = movement.endPosition.y - 25 + "px";
        tooltip.innerHTML ='<p>单击开始，右击结束</p>';
		cartesian = viewer.scene.pickPosition(movement.endPosition); 
		//cartesian = viewer.scene.camera.pickEllipsoid(movement.endPosition, viewer.scene.globe.ellipsoid);
		if(positions.length >= 2){
			if (!Cesium.defined(polygon)) {
				polygon = new PolygonPrimitive(positions);
			}else{
				positions.pop();
				// cartesian.y += (1 + Math.random());
				positions.push(cartesian);
			}
			// tooltip.innerHTML='<p>'+distance+'米</p>';
		}
	},Cesium.ScreenSpaceEventType.MOUSE_MOVE);
	
	handler.setInputAction(function(movement){
		tooltip.style.display = "none";
		cartesian = viewer.scene.pickPosition(movement.position); 
		// cartesian = viewer.scene.camera.pickEllipsoid(movement.position, viewer.scene.globe.ellipsoid);
		if(positions.length == 0) {
			positions.push(cartesian.clone());
		}
		//positions.pop();
		positions.push(cartesian);
		//在三维场景中添加点
		var cartographic = Cesium.Cartographic.fromCartesian(positions[positions.length - 1]);
		var longitudeString = Cesium.Math.toDegrees(cartographic.longitude);
		var latitudeString = Cesium.Math.toDegrees(cartographic.latitude);
		var heightString = cartographic.height;
		tempPoints.push({ lon: longitudeString, lat: latitudeString ,hei:heightString});
		floatingPoint = viewer.entities.add({
			name : '多边形面积',
			position : positions[positions.length - 1],			
			point : {
				pixelSize : 5,
				color : Cesium.Color.RED,
				outlineColor : Cesium.Color.WHITE,
				outlineWidth : 2,
				heightReference:Cesium.HeightReference.none 
			}
		});	
	},Cesium.ScreenSpaceEventType.LEFT_CLICK);
	 
	handler.setInputAction(function(movement){
		handler.destroy();
		positions.pop();
		//tempPoints.pop();
		viewer_g.entities.remove(floatingPoint);
		tooltip.style.display = "none";
		//在三维场景中添加点
		// var cartographic = Cesium.Cartographic.fromCartesian(positions[positions.length - 1]);
		// var longitudeString = Cesium.Math.toDegrees(cartographic.longitude);
		// var latitudeString = Cesium.Math.toDegrees(cartographic.latitude);
		// var heightString = cartographic.height;
		// tempPoints.push({ lon: longitudeString, lat: latitudeString ,hei:heightString});

		var textArea = getArea(tempPoints) + "平方公里";
		viewer.entities.add({
			name : '多边形面积',
			position : positions[positions.length - 1],
			// point : {
			// 	pixelSize : 5,
			// 	color : Cesium.Color.RED,
			// 	outlineColor : Cesium.Color.WHITE,
			// 	outlineWidth : 2,
			// 	heightReference:Cesium.HeightReference.CLAMP_TO_GROUND 
			// },
			label : {
				text : textArea,
				font : '18px sans-serif',
				fillColor : Cesium.Color.GOLD,
				style: Cesium.LabelStyle.FILL_AND_OUTLINE,
				outlineWidth : 2,
				verticalOrigin : Cesium.VerticalOrigin.BOTTOM,
				pixelOffset : new Cesium.Cartesian2(20, -40)
			}
		});		
    }, Cesium.ScreenSpaceEventType.LEFT_DOUBLE_CLICK );	

	var radiansPerDegree = Math.PI / 180.0;//角度转化为弧度(rad) 
	var degreesPerRadian = 180.0 / Math.PI;//弧度转化为角度
	
	//计算多边形面积
	function getArea(points) {
		
		var res = 0;
		//拆分三角曲面

		for (var i = 0; i < points.length - 2; i++) {
			var j = (i + 1) % points.length;
			var k = (i + 2) % points.length;
			var totalAngle = Angle(points[i], points[j], points[k]);

			
			var dis_temp1 = distance(positions[i], positions[j]);
			var dis_temp2 = distance(positions[j], positions[k]);
			res += dis_temp1 * dis_temp2 * Math.abs(Math.sin(totalAngle)) ;
			console.log(res);
		}
		
		
		return (res/1000000.0).toFixed(4);
	}

	/*角度*/
    function Angle(p1, p2, p3) {
        var bearing21 = Bearing(p2, p1);
        var bearing23 = Bearing(p2, p3);
        var angle = bearing21 - bearing23;
        if (angle < 0) {
            angle += 360;
        }
        return angle;
    }
    /*方向*/
    function Bearing(from, to) {
        var lat1 = from.lat * radiansPerDegree;
        var lon1 = from.lon * radiansPerDegree;
        var lat2 = to.lat * radiansPerDegree;
        var lon2 = to.lon * radiansPerDegree;
        var angle = -Math.atan2(Math.sin(lon1 - lon2) * Math.cos(lat2), Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1) * Math.cos(lat2) * Math.cos(lon1 - lon2));
        if (angle < 0) {
            angle += Math.PI * 2.0;
        }
        angle = angle * degreesPerRadian;//角度
        return angle;
    } 

	var PolygonPrimitive = (function(){
		function _(positions){
			this.options = {
				name:'多边形',
				polygon : {
					hierarchy : [],
					perPositionHeight : true,
					material : Cesium.Color.GREEN.withAlpha(0.5)
				}
			};
			
			this.hierarchy = positions;
			this._init();
		}
	
		_.prototype._init = function(){
			var _self = this;
			var _update = function(){
				return _self.hierarchy;
			};
			//实时更新polygon.hierarchy
			this.options.polygon.hierarchy = new Cesium.CallbackProperty(_update,false);
			viewer.entities.add(this.options);
		};
	
		return _;
	})();

	function distance(point1,point2){
		var point1cartographic = Cesium.Cartographic.fromCartesian(point1);
		var point2cartographic = Cesium.Cartographic.fromCartesian(point2);
		/**根据经纬度计算出距离**/
		var geodesic = new Cesium.EllipsoidGeodesic();
		geodesic.setEndPoints(point1cartographic, point2cartographic);
		var s = geodesic.surfaceDistance;
		//console.log(Math.sqrt(Math.pow(distance, 2) + Math.pow(endheight, 2)));
		//返回两点之间的距离
		s = Math.sqrt(Math.pow(s, 2) + Math.pow(point2cartographic.height - point1cartographic.height, 2));	
		return s;
	}
};