如何获得巴比伦的网状中心?

双击网格后,我需要找出网格的中心相对于其边界框的位置

    window.addEventListener("dblclick", function (event) {
        var pickResult = scene.pick(scene.pointerX, scene.pointerY);
        var mesh = pickResult.pickedMesh;
        //var centerPosition = mesh.GetCenter(); <-- what is the center             
    });