Open CASCADE学习|保存为STL文件

STL (Stereolithography) 文件是一种广泛用于3D打印和计算机辅助设计 (CAD) 领域的文件格式。它描述了一个三维模型的表面而不包含颜色、材质或其他非几何信息。STL文件通常用于3D打印过程中，因为它们仅包含构建物体所需的位置信息。

由于STL文件只包含表面信息，因此在导出过程中可能会丢失一些细节，特别是当模型具有非常小的特征或内部几何结构时。因此，在导出之前，最好确保你的模型是“水密的”（即没有内部孔或洞），并且所有的细节都在可接受的打印分辨率内。

为了将一个3D模型保存为STL文件，你通常需要使用一个3D建模软件或CAD软件，如SolidWorks、Fusion 360、Blender、Tinkercad等。

下面基于OCCT实现将3D模型保存为STL文件：

void SaveFile(const QString filename)
{
    std::fstream fs;
    fs.open(filename.toStdString(), std::ios::out);
    bool flag = fs.is_open();

    fs << "solid OCC STL\n";
    TopoDS_Shape aBottle = MakeBottle(50, 70, 30);
    IMeshTools_Parameters aMeshParams;  //离散化的参数
    BRepMesh_IncrementalMesh::SetParallelDefault(true);
    for (TopExp_Explorer Ex(aBottle, TopAbs_FACE); Ex.More(); Ex.Next())
    {
        TopoDS_Face aFace = TopoDS::Face(Ex.Current());
        //划分网格
        BRepMesh_IncrementalMesh aMesher(aFace, aMeshParams);
        const Standard_Integer aStatus = aMesher.GetStatusFlags();
        //读取网格
        TopLoc_Location  loc = aFace.Location();
        const  Poly_ListOfTriangulation triangulars = BRep_Tool::Triangulations(aFace, loc); //容器
        int num = triangulars.Size();

        Poly_ListOfTriangulation::iterator iter = triangulars.begin();
        for (iter; iter != triangulars.end(); iter++) {
            Handle(Poly_Triangulation) poy = *iter;
            Standard_Integer nodNum = poy->NbTriangles();
            bool f = poy->HasNormals();
            for (int i = 1; i <= nodNum; i++) {
                Poly_Triangle tri = poy->Triangle(i);

                Standard_Integer n1, n2, n3;
                tri.Get(n1, n2, n3); //得到三角形三个顶点编号

                //计算三角形面片的法线
                double x1 = poy->Node(n1).X();
                double y1 = poy->Node(n1).Y();
                double z1 = poy->Node(n1).Z();

                double x2 = poy->Node(n2).X();
                double y2 = poy->Node(n2).Y();
                double z2 = poy->Node(n2).Z();

                double x3 = poy->Node(n3).X();
                double y3 = poy->Node(n3).Y();
                double z3 = poy->Node(n3).Z();

                double detX1 = x2 - x1;
                double detY1 = y2 - y1;
                double detZ1 = z2 - z1;

                double detX2 = x3 - x2;
                double detY2 = y3 - y2;
                double detZ2 = z3 - z2;

                double X = detY1 * detZ2 - detZ1 * detY2;
                double Y = detZ1 * detX2 - detX1 * detZ2;
                double Z = detX1 * detY2 - detY1 * detX2;

                double module = std::pow(X * X + Y * Y + Z * Z, 0.5);
                X /= module;
                Y /= module;
                Z /= module;

                //gp_Dir normal = poy->Normal(i);

                fs << " facet normal  " << X << " " << Y << " " << Z << "\n";
                fs << "  outer loop" << "\n";
                fs << "   vertex  " << poy->Node(n1).X() << " " << poy->Node(n1).Y() << " " << poy->Node(n1).Z() << "\n";
                //std::cout<< "   vertex  " << poy->Node(n1).X() << " " << poy->Node(n1).Y() << " " << poy->Node(n1).Z() << "\n";
                fs << "   vertex  " << poy->Node(n2).X() << " " << poy->Node(n2).Y() << " " << poy->Node(n2).Z() << "\n";
                fs << "   vertex  " << poy->Node(n3).X() << " " << poy->Node(n3).Y() << " " << poy->Node(n3).Z() << "\n";
                fs << "  endloop" << "\n";
                fs << " endfacet" << "\n";
            }
        }
    }
    fs << "endsolid OCC STL\n";
    fs.close();
}