3D-Tiles 矩形裁切

// 第一个参数是切割的primitive对象  第二个是四个点的坐标
const ClipRectangle = (clipObj, positions) => {
    //计算坐标转换需要用到的矩阵的方法,参数：模型
    function getInverseTransform (tileSet) {
        let transform
        let tmp = tileSet.root.transform
        if ((tmp && tmp.equals(Cesium.Matrix4.IDENTITY)) || !tmp) {
            // 如果root.transform不存在，则3DTiles的原点变成了boundingSphere.center
            transform = Cesium.Transforms.eastNorthUpToFixedFrame(tileSet.boundingSphere.center)
        } else {
            transform = Cesium.Matrix4.fromArray(tileSet.root.transform)
        }
        return Cesium.Matrix4.inverseTransformation(transform, new Cesium.Matrix4())
    }

    //对点进行坐标转换的方法
    function getOriginCoordinateSystemPoint (point, inverseTransform) {
        let val = Cesium.Cartesian3.fromDegrees(point.lng, point.lat)
        return Cesium.Matrix4.multiplyByPoint(inverseTransform, val, new Cesium.Cartesian3(0, 0, 0))
    }

    function createPlane (p1, p2, inverseTransform) {
        // 将仅包含经纬度信息的p1,p2，转换为相应坐标系的cartesian3对象
        let p1C3 = getOriginCoordinateSystemPoint(p1, inverseTransform)
        let p2C3 = getOriginCoordinateSystemPoint(p2, inverseTransform)
        
        // 定义一个垂直向上的向量up
        let up = new Cesium.Cartesian3(0, 0, 10)
        //  right 实际上就是由p1指向p2的向量
        let right = Cesium.Cartesian3.subtract(p1C3, p2C3, new Cesium.Cartesian3())
        
        // 计算normal， right叉乘up，得到平面法向量，这个法向量指向right的右侧
        let normal = Cesium.Cartesian3.cross(right, up, new Cesium.Cartesian3())
        normal = Cesium.Cartesian3.normalize(normal, normal)

        //由于已经获得了法向量和过平面的一点，因此可以直接构造Plane,并进一步构造ClippingPlane
        let planeTmp = Cesium.Plane.fromPointNormal(p1C3, normal)
        return Cesium.ClippingPlane.fromPlane(planeTmp)
    }

    var latLngArr = positions

    var clippingPlanesss0 = createPlane(latLngArr[0], latLngArr[1], getInverseTransform(clipObj))
    var clippingPlanesss1 = createPlane(latLngArr[1], latLngArr[2], getInverseTransform(clipObj))
    var clippingPlanesss2 = createPlane(latLngArr[2], latLngArr[3], getInverseTransform(clipObj))
    var clippingPlanesss3 = createPlane(latLngArr[3], latLngArr[0], getInverseTransform(clipObj))

    var plane0 = new Cesium.ClippingPlane(clippingPlanesss0.normal, clippingPlanesss2.distance * -1)
    var plane1 = new Cesium.ClippingPlane(clippingPlanesss1.normal, clippingPlanesss3.distance * -1)
    var plane2 = new Cesium.ClippingPlane(clippingPlanesss2.normal, clippingPlanesss0.distance * -1)
    var plane3 = new Cesium.ClippingPlane(clippingPlanesss3.normal, clippingPlanesss1.distance * -1)
    
    let clippingPlanes = new Cesium.ClippingPlaneCollection({
        // 切面
        planes: [plane0, plane1, plane2, plane3],
        unionClippingRegions: false,
        edgeWidth: 2.0,// 切面与模型相交线的线宽，如果不需要切面边线，可设置为0
        edgeColor: Cesium.Color.WHITE, // 平面切割时模型的边缘颜色
    })
    
    clipObj.clippingPlanes = clippingPlanes
}