序言,VTK介绍:
VTK 全称为 The Visualization Toolkit
(可视化工具),是一个开源、跨平台、自由获取、支持并行计算的图形应用函数;拥有3D 渲染的最新工具、提供3D交互模式以及2D绘图等。
VTK 包含一个C++类库,目前提供了众多语言接口,例如 Java、Python、TCL
;在三维函数库OpenGL
的基础上采用面向对象设计方法发展起来
图形学基本概念和数据结构,是VTK的核心,VTK是通过 Pipline
的形式来输送数据,实现预览效果。
三维重建
在 VTK 中,提供了两种重建方式:体绘制和面绘制 (一般来说用VTK做重建,医学图像领域较多,如 Dicom、mha、mhd
;当然 VTK 也实现点云重建)
面绘制
利用面绘值用到VTK封装到的 Marching Cube
算法,简称 MC
算法,MC
算法的实现主要分为三部分:
1,确定包含等值面的体元
首先介绍一下 体元的概念,体元是三维图像中由相邻的八个体素点组成的正方体方格,英语也叫 Cube,体元中角点函数值分为两种情况,一种是大于等于给定等值面的值 C0 ,则将角点设为 1 称该角点在等值面内部,否则设为0,在等值面之外,
一般来说,会出现一个角点在内,一个角点在外,则角点之间的连线(也就是体元的边)必然与等值面相交,根据这个原理就能判断等值面与哪些体元相交。
体元内每个角点(顶点)有两种情况:0和1,一共8个角点即分为256种( 2 8 = 256 2^8 = 2562
8
=256 ),根据平面对称性、中心对称性,256种最终降到15种
2,确定等值面与体元边界的交点
找到含有等值面的体元之后,接下来就是确定等值面与体元边界的交点,体元间的数值都是呈线性变化,求交点时一般采用的是线性插值,如 Case0 中等值面的两个端点 一个在外为( 标记0) ,一个在内 ( 标记为1 ) 则交点为0.5;
3,求等值面的法向量
以上步骤 1,2,3 为实现 MC 算法步骤流程,但利用 VTK ,不需要这么繁琐,主要算法步骤都已经封装到 vtkMarchingCube 类中,使用 vtkMarchingCube 时,需要设置三个参数:
SetValue(int i,double value) 设置第i 个等值面的值b,(提醒一下,医学图像中的灰度值范围不是 0-256 而是0-65326,但大部分取值范围都在0-1000)。
SetNumberofContours(int number),设置等值面的个数
ComputerNormalsOn() 设置计算等值面的法向量,提高渲染质量;
上面这张图显示的就是 vtk 呈像的基本流程,下面是仿照官网写的用面绘制来对图像重建的代码部分:
#include<vtkRenderWindow.h> #include<vtkRenderWindowInteractor.h> #include<vtkDICOMImageReader.h> #include<vtkMarchingCubes.h> #include<vtkPolyDataMapper.h> #include<vtkStripper.h> #include<vtkActor.h> #include<vtkProperty.h> #include<vtkCamera.h> #include<vtkOutlineFilter.h> #include<vtkOBJExporter.h> #include<vtkRenderer.h> #include<vtkMetaImageReader.h> #include<vtkInteractorStyleTrackballCamera.h> #include<iostream> #include<string.h> //需要进行初始化,否则会报错 #include <vtkAutoInit.h> #include<vtkRenderingVolumeOpenGL2ObjectFactory.h> #include<vtkRenderingOpenGL2ObjectFactory.h> using namespace std; int main() { ///Marching Cube; vtkObjectFactory::RegisterFactory(vtkRenderingOpenGL2ObjectFactory::New()); vtkObjectFactory::RegisterFactory(vtkRenderingVolumeOpenGL2ObjectFactory::New()); vtkSmartPointer<vtkRenderer> ren = vtkSmartPointer<vtkRenderer>::New(); vtkSmartPointer<vtkRenderWindow> renWin = vtkSmartPointer<vtkRenderWindow>::New();//WINDOW; renWin->AddRenderer(ren); vtkSmartPointer<vtkRenderWindowInteractor> iren = vtkSmartPointer<vtkRenderWindowInteractor>::New();//wininteratcor; iren->SetRenderWindow(renWin); vtkSmartPointer<vtkDICOMImageReader> reader = vtkSmartPointer<vtkDICOMImageReader>::New(); reader->SetDirectoryName("E:/DIcom_Data/DICOM"); reader->SetDataByteOrderToLittleEndian(); reader->Update(); /*vtkDICOMImageReader *reader = vtkDICOMImageReader::New(); reader->SetDirectoryName("E:/Coding Pra/VTK/VTK_Examples_StandardFormats_Input_DicomTestImages/DICOM"); reader->SetDataByteOrderToLittleEndian(); reader->Update();*/ cout << "读取数据完毕" << endl; cout << "The width is" << reader->GetWidth() << endl; cout << "The height is" << reader->GetHeight() << endl; cout << "The depth is" << reader->GetPixelSpacing() << endl; cout << "The Output port is" << reader->GetOutputPort() << endl; vtkSmartPointer<vtkMarchingCubes> marchingcube = vtkSmartPointer<vtkMarchingCubes>::New(); marchingcube->SetInputConnection(reader->GetOutputPort());//获得读取的数据的点集; marchingcube->SetValue(0, 200);//Setting the threshold; marchingcube->ComputeNormalsOn();//计算表面法向量; vtkSmartPointer<vtkStripper> Stripper = vtkSmartPointer<vtkStripper>::New(); Stripper->SetInputConnection(marchingcube->GetOutputPort());//获取三角片 vtkSmartPointer<vtkPolyDataMapper> Mapper = vtkSmartPointer<vtkPolyDataMapper>::New();//将三角片映射为几何数据; Mapper->SetInputConnection(Stripper->GetOutputPort()); Mapper->ScalarVisibilityOff();// vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();//Created a actor; actor->SetMapper(Mapper);//获得皮肤几何数据 actor->GetProperty()->SetDiffuseColor(1, .49, .25);//设置皮肤颜色; actor->GetProperty()->SetSpecular(0.3);//反射率; actor->GetProperty()->SetOpacity(1.0);//透明度; actor->GetProperty()->SetSpecularPower(20);//反射光强度; actor->GetProperty()->SetColor(1, 0, 0);//设置角的颜色; actor->GetProperty()->SetRepresentationToWireframe();//线框; //vtkSmartPointer<vtkCamera> camera = vtkSmartPointer<vtkCamera>::New();//Setting the Camera; //camera->SetViewUp(0, 0, -1);//设置相机向上方向; //camera->SetPosition(0, 1, 0);//位置:世界坐标系,相机位置; //camera->SetFocalPoint(0, 0, 0);//焦点,世界坐标系,控制相机方向; //camera->ComputeViewPlaneNormal();//重置视平面方向,基于当前的位置和焦点; vtkSmartPointer<vtkOutlineFilter> outfilterline = vtkSmartPointer<vtkOutlineFilter>::New(); outfilterline->SetInputConnection(reader->GetOutputPort()); vtkSmartPointer<vtkPolyDataMapper> outmapper = vtkSmartPointer<vtkPolyDataMapper>::New(); outmapper->SetInputConnection(outfilterline->GetOutputPort()); vtkSmartPointer<vtkActor> OutlineActor = vtkSmartPointer<vtkActor>::New(); OutlineActor->SetMapper(outmapper); OutlineActor->GetProperty()->SetColor(0, 0, 0);//线框颜色 ren->AddActor(actor); ren->AddActor(OutlineActor); //ren->SetActiveCamera(camera);//设置渲染器的相机; ren->ResetCamera(); ren->ResetCameraClippingRange(); //camera->Dolly(1.5);//使用Dolly()方法延伸着视平面法向移动相机; ren->SetBackground(1, 1, 1);//设置背景颜色; renWin->SetSize(1000, 600); vtkInteractorStyleTrackballCamera *style = vtkInteractorStyleTrackballCamera::New(); iren->SetInteractorStyle(style); renWin->Render(); iren->Initialize(); iren->Start(); vtkSmartPointer<vtkOBJExporter> porter = vtkSmartPointer<vtkOBJExporter>::New(); porter->SetFilePrefix("E:/ceshi/aaa/regist_after/polywrite.obj");//重建图像输出 porter->SetInput(renWin); porter->Write(); return EXIT_SUCCESS; }
上面就是 VTK 基于 Marching Cube算法
实现的重建效果:
体绘制重建
体绘制时分为两部分
1,定义 vtkVoluemRayCastMapper 对象
体绘制中最常用的方法 ;vtkVolumeRayCastMapper() 光线投影,体绘制时,首先定义一个Mapper 然后接受两个输入:
SetInput(vtkImageDate *) 用于设置输入图像数据;
SetVolumeRayCastFunction(vtkVolumeRayCastFunction *) 用于设置光线投影函数类型;
2,利用 vtkVolumeProperty 定义体绘制属性;
SetScalarOpacity() 设置灰度不透明函数;
SetColor() 颜色传输函数;
3, 定义 vtkVolume 对象接收 Mapper对象和 Property 对象
SetMapper()接受 Mapper 对象;
SetProperty() 接受 Property 对象;
vtk 中体绘制 核心就是改变 Mapper 和 vtkVolumeRayCastFunction() ,上面中vtkColumeRayCastMapper 只是 VolumeMapper 其中的一种,且投影函数类 vtkVolumeRayCastFunction 一共有三个子类:
vtkVolumeRayCastCompositeFunction
vtkVolumeRayCasMIPFunction、
vtkVolumeRayCastIsosurfaceFunction,
因此,其细分的话vtk中的体绘制也不止一种
而下面这个是最常用到的(``vtkVolumeRayCastMapper+vtkVolumeRayCastCompositeFunction`)
//体绘制 #include<vtkRenderWindowInteractor.h> #include<vtkDICOMImageReader.h> #include<vtkCamera.h> #include<vtkActor.h> #include<vtkRenderer.h> #include<vtkVolumeProperty.h> #include<vtkProperty.h> #include<vtkPolyDataNormals.h> #include<vtkImageShiftScale.h> #include "vtkVolumeRayCastMapper.h" #include<vtkPiecewiseFunction.h> #include<vtkColorTransferFunction.h> #include<vtkVolumeRayCastCompositeFunction.h> #include<vtkRenderWindow.h> #include<vtkImageCast.h> #include<vtkVolumeRayCastCompositeFunction.h> #include<vtkOBJExporter.h> #include<vtkOutlineFilter.h> #include<vtkPolyDataMapper.h> #include<vtkInteractorStyleTrackballCamera.h> #include<vtkRenderingVolumeOpenGL2ObjectFactory.h> #include<vtkRenderingOpenGL2ObjectFactory.h> #include<vtkMetaImageReader.h> #include<vtkLODProp3D.h> //体绘制加速 //Gpu光照映射 #include<vtkGPUVolumeRayCastMapper.h> #include<iostream> int main() { vtkObjectFactory::RegisterFactory(vtkRenderingOpenGL2ObjectFactory::New()); vtkObjectFactory::RegisterFactory(vtkRenderingVolumeOpenGL2ObjectFactory::New()); //定义绘制器; vtkRenderer *aRenderer = vtkRenderer::New();//指向指针; vtkSmartPointer<vtkRenderWindow> renWin = vtkSmartPointer<vtkRenderWindow>::New(); renWin->AddRenderer(aRenderer); vtkRenderWindowInteractor *iren = vtkRenderWindowInteractor::New(); iren->SetRenderWindow(renWin); //读取数据; /*vtkDICOMImageReader *reader = vtkDICOMImageReader::New(); reader->SetDirectoryName("E:/Coding Pra/VTK/VTK_Examples_StandardFormats_Input_DicomTestImages/DICOM"); reader->SetDataByteOrderToLittleEndian();*/ vtkSmartPointer<vtkDICOMImageReader> reader = vtkSmartPointer<vtkDICOMImageReader>::New(); reader->SetDirectoryName("E:/DIcom_Data/DICOM"); reader->SetDataByteOrderToLittleEndian(); //图像数据预处理,类型转换:通过 vtkimageCast 将不同类型数据集转化为 vtk 可以处理的数据集; vtkImageCast *cast_file = vtkImageCast::New(); cast_file->SetInputConnection(reader->GetOutputPort()); cast_file->SetOutputScalarTypeToUnsignedShort(); cast_file->Update(); //透明度映射函数定义; vtkPiecewiseFunction *opacityTransform = vtkPiecewiseFunction::New(); opacityTransform->AddPoint(0, 0.0); opacityTransform->AddPoint(20, 0.0); opacityTransform->AddPoint(200, 1.0); opacityTransform->AddPoint(300, 1.0); //颜色映射函数定义,梯度上升的 vtkColorTransferFunction *colorTransformFunction = vtkColorTransferFunction::New(); colorTransformFunction->AddRGBPoint(0.0, 0.0, 0.0, 0.0); colorTransformFunction->AddRGBPoint(64.0, 0.0, 0.0, 0.0); colorTransformFunction->AddRGBPoint(128.0, 1.0, 0.0, 0.0); colorTransformFunction->AddRGBPoint(192.0, 1.0, 0.0, 0.0); colorTransformFunction->AddRGBPoint(255.0, 1.0, 0.0, 0.0); vtkPiecewiseFunction *gradientTransform = vtkPiecewiseFunction::New(); gradientTransform->AddPoint(0, 0.0); gradientTransform->AddPoint(20, 2.0); gradientTransform->AddPoint(200, 0.1); gradientTransform->AddPoint(300, 0.1); //体数据属性; vtkVolumeProperty *volumeProperty = vtkVolumeProperty::New(); volumeProperty->SetColor(colorTransformFunction); volumeProperty->SetScalarOpacity(opacityTransform); volumeProperty->SetGradientOpacity(gradientTransform); volumeProperty->ShadeOn();//应用 volumeProperty->SetInterpolationTypeToLinear();//直线间样条插值; volumeProperty->SetAmbient(0.4);//环境光系数; volumeProperty->SetDiffuse(0.6);//漫反射; volumeProperty->SetSpecular(0.2); volumeProperty->SetSpecularPower(10);//高光强度; 计算光照效应;利用 vtkBolumeRayCaseMapper进行计算; //vtkVolumeRayCastMapper *volunemapper = vtkVolumeRayCastMapper::New(); //vtkVolumeRayCastCompositeFunction *compositeFunction = vtkVolumeRayCastCompositeFunction::New(); //光纤映射类型定义: vtkSmartPointer<vtkVolumeRayCastCompositeFunction> compositecast = vtkSmartPointer<vtkVolumeRayCastCompositeFunction>::New(); //Mapper定义, vtkSmartPointer<vtkVolumeRayCastMapper> hiresMapper = vtkSmartPointer<vtkVolumeRayCastMapper>::New(); hiresMapper->SetInputData(cast_file->GetOutput()); hiresMapper->SetVolumeRayCastFunction(compositecast); vtkSmartPointer<vtkLODProp3D> prop = vtkSmartPointer<vtkLODProp3D>::New(); prop->AddLOD(hiresMapper,volumeProperty,0.0); // //volunemapper->SetVolumeRayCastFunction(compositeFunction);//载入体绘制方法; //volunemapper->SetInputConnection(cast_file->GetOutputPort()); //vtkFixedPointVolumeRayCastMapper *fixedPointVolumeMapper = vtkFixedPointVolumeRayCastMapper::New() //fixedPointVolumeMapper->SetInput() vtkVolume *volume = vtkVolume::New(); volume->SetMapper(hiresMapper); volume->SetProperty(volumeProperty);//设置体属性; double volumeView[4] = { 0,0,0.5,1 }; vtkOutlineFilter *outlineData = vtkOutlineFilter::New();//线框; outlineData->SetInputConnection(reader->GetOutputPort()); vtkPolyDataMapper *mapOutline = vtkPolyDataMapper::New(); mapOutline->SetInputConnection(outlineData->GetOutputPort()); vtkActor *outline = vtkActor::New(); outline->SetMapper(mapOutline); outline->GetProperty()->SetColor(0, 0, 0);//背景纯黑色; aRenderer->AddVolume(volume); aRenderer->AddActor(outline); aRenderer->SetBackground(1, 1, 1); aRenderer->ResetCamera(); //重设相机的剪切范围; aRenderer->ResetCameraClippingRange(); renWin->SetSize(800, 800); renWin->SetWindowName("测试"); vtkRenderWindowInteractor *iren2 = vtkRenderWindowInteractor::New(); iren2->SetRenderWindow(renWin); //设置相机跟踪模式 vtkInteractorStyleTrackballCamera *style = vtkInteractorStyleTrackballCamera::New(); iren2->SetInteractorStyle(style); renWin->Render(); iren2->Initialize(); iren2->Start(); vtkOBJExporter *porter = vtkOBJExporter::New(); porter->SetFilePrefix("E:/ceshi/aaa/regist_after/esho.obj"); porter->SetInput(renWin); porter->Write(); porter->Update(); return EXIT_SUCCESS; }
上面是体绘制的结果,相对来说体绘制需要计算资源更大些, vtk 在这方面有所考虑,提供了vtKGPUVolumeRayCastMapper GUP 加速的光线投射算法。