首先來看一下Frustum的文件：Frustum幫助文件

根據文件建立一個Frustum：

function initFrustum()
        {
            //定義錐形物體最遠的四個點
            var topLeftPoint = new THREE.Vector3(-2000,2000,-1000);
            var topRightPoint= new THREE.Vector3(2000,2000,-1000);
            var bottomLeftPoint = new THREE.Vector3(-2000, -2000, -1000);
            var bottomRightPoint = new THREE.Vector3(2000, -2000, -1000);
            //定義錐形物體最近的四個點
            var nearTopLeftPoint = new THREE.Vector3(-2000, 2000, 1000);
            var nearTopRightPoint = new THREE.Vector3(2000, 2000, 1000);
            var nearBottomLeftPoint = new THREE.Vector3(-2000, -2000, 1000);
            var nearBottomRightPoint = new THREE.Vector3(2000, -2000, 1000);
            topPlane = new THREE.Plane();
            bottomPlane = new THREE.Plane();
            rightPlane = new THREE.Plane();
            leftPlane = new THREE.Plane();
            nearPlane = new THREE.Plane();
            farPlane = new THREE.Plane();
            topPlane.setFromCoplanarPoints(nearTopLeftPoint, topLeftPoint, topRightPoint);
            leftPlane.setFromCoplanarPoints(nearTopLeftPoint, topLeftPoint, bottomLeftPoint);
            bottomPlane.setFromCoplanarPoints(nearBottomLeftPoint, bottomLeftPoint, bottomRightPoint);
            rightPlane.setFromCoplanarPoints(nearBottomRightPoint, bottomRightPoint, topRightPoint);
            farPlane.setFromCoplanarPoints(topLeftPoint, topRightPoint, bottomLeftPoint);
            nearPlane.setFromCoplanarPoints(nearTopLeftPoint,nearTopRightPoint,nearBottomLeftPoint);
            frustum = new THREE.Frustum(topPlane,leftPlane,bottomPlane,rightPlane,farPlane,nearPlane);
        }
 

接著前面兩章，把判斷選中的改為：

frustum.intersectsObject(intersects[0].object)

就可以直觀的看到相交的結果。

最後可以直觀的看到結果：相交的時候返回True.從原始碼中可以看到相交和包含返回一樣的值。如果想把相交和包含區分開來，需要進一步處理。另外，這裡的結果不一定正確，這裡是取的是包含物體sphere，所以有些情況下，實際沒有相交，會被判斷為相交。

Frustum原始碼