如何访问web IFC三中IFC项的BufferGeometry

Question

我正在尝试获取元素的几何图形即对应于我所具有的expressId的BufferGeometry对象(不是通过拾取(。

基本上，我在问如何遍历IFC模型并将每个对象导出为一个单独的OBJ

我要注意的是，对于某些版本的包，我有反向工程代码来实现这一点，但它使用了未记录的功能，所以在后来的版本中自然会中断(代码还根据材料的颜色为几何体着色，所以我不需要mtl(：

不要复制此代码，它将不起作用

Object.values(bimModel.ifcManager.state.models[bimModel.modelID].items).forEach(type => {
Object.entries(type.geometries).forEach(([id, geometry]) => {
const properties = bimModel.getItemProperties(Number(id))
const numVertices = geometry.getAttribute('position').count
const color = type.material.color.toArray().map(x => x * 255)
const vertexColors = new Uint8Array(Array.from({ length: numVertices }, () => color).flat())
geometry.setAttribute('color', new BufferAttribute(vertexColors, 3, true))
})
})

Answer 1

这正是我们将模型导出到glTF的方法。基本工作流程是：

• 决定要导出的IFC类别
• 获取每个类别的所有项目
• 重建每个项目的网格
• 使用您选择的Three.js导出器导出网格

让我们看一个从墙上获取所有网格的基本示例。这个过程不像将每个IFC项作为一个单独的网格那么简单，但这是绘制调用的最低代价(否则，浏览器甚至无法容纳中等大小的IFC文件(：

import { IFCWALLSTANDARDCASE } from 'web-ifc';
async function getAllWallMeshes() {
// Get all the IDs of the walls
const wallsIDs = manager.getAllItemsOfType(0, IFCWALL, false);
const meshes = [];
const customID = 'temp-gltf-subset';
for (const wallID of wallsIDs) {
const coordinates = [];
const expressIDs = [];
const newIndices = [];
const alreadySaved = new Map();
// Get the subset for the wall
const subset = viewer.IFC.loader.ifcManager.createSubset({
ids: [wallID],
modelID,
removePrevious: true,
customID
});
// Subsets have their own index, but share the BufferAttributes 
// with the original geometry, so we need to rebuild a new 
// geometry with this index
const positionAttr = subset.geometry.attributes.position;
const expressIDAttr = subset.geometry.attributes.expressID;
const newGroups = subset.geometry.groups
.filter((group) => group.count !== 0);
const newMaterials = [];
const prevMaterials = subset.material;
let newMaterialIndex = 0;
newGroups.forEach((group) => {
newMaterials.push(prevMaterials[group.materialIndex]);
group.materialIndex = newMaterialIndex++;
});
let newIndex = 0;
for (let i = 0; i < subset.geometry.index.count; i++) {
const index = subset.geometry.index.array[i];
if (!alreadySaved.has(index)) {
coordinates.push(positionAttr.array[3 * index]);
coordinates.push(positionAttr.array[3 * index + 1]);
coordinates.push(positionAttr.array[3 * index + 2]);
expressIDs.push(expressIDAttr.getX(index));
alreadySaved.set(index, newIndex++);
}
const saved = alreadySaved.get(index);
newIndices.push(saved);
}
const geometryToExport = new BufferGeometry();
const newVerticesAttr = new BufferAttribute(Float32Array.from(coordinates), 3);
const newExpressIDAttr = new BufferAttribute(Uint32Array.from(expressIDs), 1);
geometryToExport.setAttribute('position', newVerticesAttr);
geometryToExport.setAttribute('expressID', newExpressIDAttr);
geometryToExport.setIndex(newIndices);
geometryToExport.groups = newGroups;
geometryToExport.computeVertexNormals();
const mesh = new Mesh(geometryToExport, newMaterials);
meshes.push(mesh);
}
viewer.IFC.loader.ifcManager.removeSubset(modelID, undefined, customID);
return meshes;
}