使用cesium，进行贴地面积量算

    viewer.cesiumWidget.screenSpaceEventHandler.removeInputAction(Cesium.ScreenSpaceEventType.LEFT_DOUBLE_CLICK);
    //绘制点
    function createPoint(worldPosition) {
        console.log(worldPosition.x);
        if (worldPosition.x != NaN && worldPosition.y != NaN && worldPosition.z != NaN) {
            var point = viewer.entities.add({
                position: worldPosition,
                name: 'pointer',
                point: {
                    color: Cesium.Color.WHITE,
                    pixelSize: 10,
                    heightReference: Cesium.HeightReference.CLAMP_TO_GROUND
                }
            });
            return point;
        }

    }
    //绘制图形
    function drawShape(positionData) {
        var shape;
        //当positionData为数组时绘制最终图，如果为function则绘制动态图
        var arr = typeof positionData.getValue === 'function' ? positionData.getValue(0) : positionData;
        var ceshi = new Cesium.CallbackProperty(function () {
            var obj = new Cesium.PolygonHierarchy(arr);
            console.log(obj.positions)
            return obj.positions;
        }, false);
        console.log(typeof ceshi);
        shape = viewer.entities.add({
            polygon: {
                hierarchy: arr,
                material: new Cesium.ColorMaterialProperty(Cesium.Color.ORANGE.withAlpha(0.3)),
            }
        })
        return shape;
    }
    var activeShapePoints = [];
    var activeShape;
    var floatingPoint;
    var handler = new Cesium.ScreenSpaceEventHandler(viewer.canvas);
    handler.setInputAction(function (event) {
        // We use `viewer.scene.pickPosition` here instead of `viewer.camera.pickEllipsoid` so that
        // we get the correct point when mousing over terrain.
        var earthPosition = viewer.scene.pickPosition(event.position);
        // `earthPosition` will be undefined if our mouse is not over the globe.
        if (Cesium.defined(earthPosition)) {
            if (activeShapePoints.length === 0) {
                floatingPoint = createPoint(earthPosition);
                activeShapePoints.push(earthPosition);
                var dynamicPositions = new Cesium.CallbackProperty(function () {
                    return activeShapePoints;
                }, false);
                activeShape = drawShape(dynamicPositions);
            }
            activeShapePoints.push(earthPosition);
            createPoint(earthPosition);
        }
    }, Cesium.ScreenSpaceEventType.LEFT_CLICK);

    handler.setInputAction(function (event) {
        if (Cesium.defined(floatingPoint)) {
            var newPosition = viewer.scene.pickPosition(event.endPosition);
            if (Cesium.defined(newPosition)) {
                floatingPoint.position.setValue(newPosition);
                activeShapePoints.pop();
                activeShapePoints.push(newPosition);
            }
        }
    }, Cesium.ScreenSpaceEventType.MOUSE_MOVE);
    // Redraw the shape so it's not dynamic and remove the dynamic shape.
    function terminateShape() {
        activeShapePoints.pop();
        drawShape(activeShapePoints);
        var lastRectangle = drawShape(activeShapePoints);//绘制最终图
        var coors = lastRectangle._polygon._hierarchy._value;
        var Geographys = [];
        for (var i = 0; i < coors.length; i++) {
            Geographys.push({ lon: Number(Cesium.Math.toDegrees(viewer.scene.globe.ellipsoid.cartesianToCartographic(coors[i]).longitude)), lat: Number(Cesium.Math.toDegrees(viewer.scene.globe.ellipsoid.cartesianToCartographic(coors[i]).latitude)) })
        }
        //Geography = [Cesium.Math.toDegrees(Geography.longitude), Cesium.Math.toDegrees(Geography.latitude)];
        console.log(lastRectangle, coors, Geographys, "duobianxing贴面")
        viewer.entities.remove(floatingPoint);
        viewer.entities.remove(activeShape);
        floatingPoint = undefined;
        activeShape = undefined;
        activeShapePoints = [];
        return Geographys;
    }
    handler.setInputAction(function (event) {
        var pointer = terminateShape();
        viewer.scene.globe.depthTestAgainstTerrain = false;
        handler.removeInputAction(Cesium.ScreenSpaceEventType.LEFT_CLICK);
        console.log(computeSignedArea(pointer).toFixed(1) / 1000000, pointer[0].lon, pointer[0].lat)
        var mj = (computeSignedArea(pointer) / 1000000).toFixed(1);
        viewer.entities.add({
            position: Cesium.Cartesian3.fromDegrees(pointer[0].lon, pointer[0].lat),
            label: {
                text: mj + 'k㎡',
                font: '22px Helvetica',
                fillColor: Cesium.Color.SKYBLUE,
                outlineColor: Cesium.Color.BLACK,
                outlineWidth: 2,
                style: Cesium.LabelStyle.FILL_AND_OUTLINE,
                horizontalOrigin: Cesium.HorizontalOrigin.CENTER,
                heightReference: Cesium.HeightReference.CLAMP_TO_GROUND 
            }
        });
    }, Cesium.ScreenSpaceEventType.RIGHT_CLICK);
    //计算多边形面积
    function computeSignedArea(path) {
    let radius = 6371009
    let len = path.length;
    if (len < 3) return 0;
    let total = 0;
    let prev = path[len - 1];
    let prevTanLat = Math.tan(((Math.PI / 2 - prev.lat / 180 * Math.PI) / 2));
        let prevLng = (prev.lon) / 180 * Math.PI;
    for (let i in path) {
        let tanLat = Math.tan((Math.PI / 2 -
            (path[i].lat) / 180 * Math.PI) / 2);
        let lng = (path[i].lon) / 180 * Math.PI;
        total += polarTriangleArea(tanLat, lng, prevTanLat, prevLng);
        prevTanLat = tanLat;
        prevLng = lng;
    }
    return Math.abs(total * (radius * radius));
    }
    function polarTriangleArea(tan1, lng1, tan2, lng2) {
        let deltaLng = lng1 - lng2;
        let t = tan1 * tan2;
        return 2 * Math.atan2(t * Math.sin(deltaLng), 1 + t * Math.cos(deltaLng));
    }
    //清楚图层并且注销事件
    function clearAlls() {
        var clearS = viewer.entities.values;
        console.log(clearS);
        viewer.scene.globe.depthTestAgainstTerrain = false;
        handler.removeInputAction(Cesium.ScreenSpaceEventType.LEFT_CLICK);
        for (var i = 0; i < clearS.length; i++) {
            viewer.entities.removeById(clearS[i]._id)
            i--;
        }
        console.log(clearS)
        getdata_ZHDPage();
    }