当前位置：首页 > news >正文

Open CASCADE学习|几何体切片处理：OpenMP与OSD_Parallel并行方案深度解析

news 来源：原创 2025/5/19 7:21:35

在三维建模与仿真领域，几何体切片处理是CAE前处理、3D打印路径规划、医学影像分析等场景的关键技术。其核心目标是将三维模型沿特定方向离散为二维截面集合，便于后续分析或制造。OpenCASCADE作为开源几何内核，提供高效的布尔运算与几何算法，可实现高精度切片处理。本文以圆锥体Z轴离散为例，深入探讨串行与并行方案的实现差异。

一、技术背景与核心需求

几何体切片处理通过离散化三维模型获取截面特征，其数学本质为平面与几何体的布尔求交运算。对于圆锥体，截面满足方程：

$k\Delta h) \cap \left(\frac{x^2 + y^2}{R^2} = \left(1 - \frac{z}{H}\right)^2\right)$

解得截面为半径渐缩的圆，满足 $ r = R(1 - z/H) )$

1.1 几何切片的应用场景

3D打印：将STL模型转换为G代码指令（每层厚度0.05~0.2mm）
有限元分析：生成结构化六面体网格（截面间距决定网格质量）
逆向工程：CT扫描点云与CAD模型的截面比对（精度要求<0.01mm）

1.2 性能挑战

计算密集型：单次布尔求交涉及B-rep拓扑遍历、曲面求根、容差处理
内存敏感：每个截面生成独立拓扑实体（Edge/Wire）
精度矛盾：容差设置与计算耗时呈指数关系（1e-6到1e-4精度差异可达10倍耗时）

二、OpenMP并行实现方案

2.1 核心代码（已验证通过）

#include <BRepPrimAPI_MakeCone.hxx>
#include <BRepAlgoAPI_Section.hxx>
#include <TopExp_Explorer.hxx>
#include <BRepAdaptor_Curve.hxx>
#include <BRep_Tool.hxx>
#include <TopoDS.hxx>
#include <Geom_ConicalSurface.hxx>
#include <iostream>
#include <vector>
#include <mutex>
#include <omp.h>// 互斥锁用于保护输出
std::mutex coutMutex;// 创建圆锥
TopoDS_Shape CreateCone(double bottomRadius, double height) {return BRepPrimAPI_MakeCone(bottomRadius, 0.0, height).Shape();
}// 处理截面结果
void ProcessSection(const TopoDS_Shape& section, double z) {std::vector<double> results;// 探索边TopExp_Explorer edgeExplorer(section, TopAbs_EDGE);while(edgeExplorer.More()){TopoDS_Edge edge = TopoDS::Edge(edgeExplorer.Current());BRepAdaptor_Curve curve(edge);if(curve.GetType() == GeomAbs_Circle){gp_Circ circle = curve.Circle();results.push_back(circle.Radius());}edgeExplorer.Next();}// 处理顶点（顶端）if(results.empty()){TopExp_Explorer vertexExplorer(section, TopAbs_VERTEX);if(vertexExplorer.More()){gp_Pnt p = BRep_Tool::Pnt(TopoDS::Vertex(vertexExplorer.Current()));{std::lock_guard<std::mutex> lock(coutMutex);std::cout << "顶点截面 z=" << z << " 位置: (" << p.X() << ", " << p.Y() << ")\n";}}return;}// 输出结果（线程安全）{std::lock_guard<std::mutex> lock(coutMutex);for(double radius : results){std::cout << "截面 z=" << z << " 半径=" << radius << " 中心坐标: (0, 0)\n";}}
}// 并行切片处理
void ParallelSliceCone(const TopoDS_Shape& cone, int numSlices, double totalHeight) {std::vector<double> zValues(numSlices + 1);double step = totalHeight / numSlices;// 预生成所有Z值#pragma omp parallel forfor(int i = 0; i <= numSlices; ++i){zValues[i] = i * step;}// 并行处理切片#pragma omp parallel for schedule(dynamic)for(size_t i = 0; i < zValues.size(); ++i){double z = zValues[i];gp_Pln slicePlane(gp_Pnt(0,0,z), gp_Dir(0,0,1));BRepAlgoAPI_Section section;section.Init1(cone);section.Init2(slicePlane);section.Build();if(section.IsDone()){ProcessSection(section.Shape(), z);}}
}int main() {const double height = 10.0;const double radius = 5.0;const int slices = 1000;  // 测试大切片数// 创建几何TopoDS_Shape cone = CreateCone(radius, height);// 并行切片double start = omp_get_wtime();ParallelSliceCone(cone, slices, height);double end = omp_get_wtime();std::cout << "\n计算完成！耗时: " << (end - start) << " 秒\n";return 0;
}

2.2 关键技术特点

内存模型：各线程独立维护拓扑实体副本
负载均衡：动态任务块（chunk=16）适应不同截面复杂度
加速瓶颈：线程数超过物理核心时出现假性加速（False Scaling）

三、OSD_Parallel原生并行方案

3.1 优化实现代码

#include <BRepPrimAPI_MakeCone.hxx>
#include <BRepAlgoAPI_Section.hxx>
#include <TopExp_Explorer.hxx>
#include <BRepAdaptor_Curve.hxx>
#include <BRep_Tool.hxx>
#include <TopoDS.hxx>
#include <Geom_ConicalSurface.hxx>
#include <OSD_Parallel.hxx>
#include <vector>
#include <mutex>
#include <iostream>
#include <omp.h>
std::mutex coutMutex;TopoDS_Shape CreateCone(double bottomRadius, double height) {return BRepPrimAPI_MakeCone(bottomRadius, 0.0, height).Shape();
}class SliceProcessor {
public:SliceProcessor(const TopoDS_Shape& cone, double totalHeight, int numSlices): myCone(cone), myTotalHeight(totalHeight), myNumSlices(numSlices) {}void operator()(int index) const {const double z = index * (myTotalHeight / myNumSlices);gp_Pln slicePlane(gp_Pnt(0, 0, z), gp_Dir(0, 0, 1));BRepAlgoAPI_Section section;section.Init1(myCone);section.Init2(slicePlane);section.Build();if (section.IsDone()) {ProcessSection(section.Shape(), z);}}private:void ProcessSection(const TopoDS_Shape& section, double z) const {std::vector<double> radii;for (TopExp_Explorer edgeExplorer(section, TopAbs_EDGE);edgeExplorer.More();edgeExplorer.Next()){const TopoDS_Edge& edge = TopoDS::Edge(edgeExplorer.Current());BRepAdaptor_Curve curve(edge);if (curve.GetType() == GeomAbs_Circle) {radii.push_back(curve.Circle().Radius());}}std::lock_guard<std::mutex> lock(coutMutex);if (!radii.empty()) {for (double r : radii) {std::cout << "截面 z=" << z<< " 半径=" << r<< " 中心坐标: (0, 0)\n";}}else {for (TopExp_Explorer vertexExplorer(section, TopAbs_VERTEX);vertexExplorer.More();vertexExplorer.Next()){gp_Pnt p = BRep_Tool::Pnt(TopoDS::Vertex(vertexExplorer.Current()));std::cout << "顶点截面 z=" << z<< " 位置: (" << p.X() << ", " << p.Y() << ")\n";}}}const TopoDS_Shape& myCone;double myTotalHeight;int myNumSlices;
};void ParallelSliceWithOCCT(const TopoDS_Shape& cone, int numSlices, double height) {SliceProcessor processor(cone, height, numSlices);// 修正参数顺序：起始索引、结束索引（不包含）、处理器对象OSD_Parallel::For(0, numSlices + 1, processor); // 7.9.0正确调用方式
}int main() {const double height = 10.0;const double radius = 5.0;const int slices = 1000;TopoDS_Shape cone = CreateCone(radius, height);double start = omp_get_wtime();ParallelSliceWithOCCT(cone, slices, height);double end = omp_get_wtime();std::cout << "\n计算完成！耗时: " << (end - start) << " 秒\n";return 0;
}