在Vue和Mapbox结合Three.js时，如何确保三维物体的底部固定在地图上而不随视角变化？

createCustomLayer(index, point, modelTransform) {
  let color;
  let altitude;

  // 根据PM2.5值设定颜色和高度 (假设此逻辑已存在)
  // ...

  const customLayer = {
    id: `custom-layer-${index}`,
    type: 'custom',
    renderingMode: '3d',
    onAdd: (map, gl) => {
      console.log(`Custom layer added: ${customLayer.id}`);
      customLayer.camera = new THREE.Camera();
      customLayer.scene = new THREE.Scene();
      // 添加光照 (环境光和定向光)
      // ... (假设此逻辑已存在)

      const geometry = new THREE.BoxGeometry(20, altitude, 20); // 调整尺寸
      const material = new THREE.MeshStandardMaterial({
        color: color,
        transparent: true,
        opacity: 0.8
      });
      const cube = new THREE.Mesh(geometry, material);

      // 添加轮廓线 (假设此逻辑已存在)
      // ...

      // **关键步骤：调整模型位置，使其底部固定在地图上**
      cube.position.set(0, altitude / 2, 0); //底部位于(0,0,0)

      customLayer.scene.add(cube);
      customLayer.map = map;
      customLayer.renderer = new THREE.WebGLRenderer({
        canvas: map.getCanvas(),
        context: gl,
        antialias: true
      });
      customLayer.renderer.autoClear = false;
    },
    render: (gl, matrix) => {
      console.log(`Custom layer rendering: ${customLayer.id}`);
      const m = new THREE.Matrix4().fromArray(matrix);
      // ... (模型变换矩阵的计算，假设此逻辑已存在)
      customLayer.camera.projectionMatrix = m.multiply(l);
      customLayer.renderer.resetState();
      customLayer.renderer.render(customLayer.scene, customLayer.camera);
      customLayer.map.triggerRepaint();
    }
  };
  return customLayer;
}