如何在ThreeJS中计算合并平面的面积

// 创建一个ThreeJS场景
var scene = new THREE.Scene();

// 添加几何体或模型到场景中
// ...

// 创建顶点数组和法向量变量
var vertices = [];
var normal = new THREE.Vector3(0, 0, 0);

// 遍历场景中的所有几何体或模型
scene.traverse(function (obj) {
  if (obj instanceof THREE.Mesh) {
    // 获取几何体的顶点信息
    var geometry = obj.geometry;
    var positionAttribute = geometry.getAttribute('position');

    // 遍历顶点坐标并保存到顶点数组中
    for (var i = 0; i < positionAttribute.count; i++) {
      var vertex = new THREE.Vector3();
      vertex.fromBufferAttribute(positionAttribute, i);
      vertices.push(vertex);
    }

    // 计算面片的法向量并相加
    for (var i = 0; i < positionAttribute.count; i += 3) {
      var v0 = vertices[i];
      var v1 = vertices[i + 1];
      var v2 = vertices[i + 2];

      var edge1 = new THREE.Vector3();
      var edge2 = new THREE.Vector3();
      edge1.subVectors(v1, v0);
      edge2.subVectors(v2, v0);

      normal.add(edge1.cross(edge2));
    }
  }
});

// 合并平面的法向量归一化
normal.normalize();

// 计算合并平面的面积
var area = 0;

for (var i = 0; i < vertices.length; i += 3) {
  var v0 = vertices[i];
  var v1 = vertices[i + 1];
  var v2 = vertices[i + 2];

  var triangleArea = normal.dot(v1.clone().sub(v0).cross(v2.clone().sub(v0))) / 2;
  area += triangleArea;
}

console.log('合并平面的面积为：', area);