1 VTK（Visualization Toolkit）是一个开源的跨平台软件系统，用于三维计算机图形学、图像处理和可视化。学习VTK的主要目的有：
- 3D可视化： VTK提供了丰富的工具和算法，可以用来可视化各种科学数据，包括医学图像、有限元分析结果、流体模拟数据等。
- 图像处理： VTK支持多种图像处理操作，如滤波、分割、配准等，可以对医学图像进行预处理和分析。
- 科学计算可视化： VTK可以与其他科学计算软件（如MATLAB、Python）结合，实现科学计算结果的可视化。
- 自定义可视化： VTK提供了灵活的接口，可以自定义各种可视化组件和交互方式，满足个性化的需求。
对于有科研需求的小伙伴，可以利用VTK将你的数据和实验结果进行可视化，对数据有一个感官的理解。比如下面的图像就是一个细胞分裂增殖的模拟图像，使用VTK对数据进行了可视化。
3图1 细胞克隆增殖的模拟
VTK就是一个工具，不用刻意的去学习它。假如你不做数据的显示，也不需要做3D模型的渲染，你就不用去学习它，因为学习任何事物都是需要学习成本的。
2 学习方法
学习VTK的方法有很多种，以下是一些建议：
- 官方文档： VTK官方文档是学习VTK最权威的资料，提供了详细的类、函数和示例。
- 教程和书籍： 网上有很多关于VTK的教程和书籍，可以帮助你快速入门。
- 示例代码： VTK提供了大量的示例代码，可以帮助你理解各种概念和用法。
- 社区： VTK有一个活跃的社区，你可以通过论坛、邮件列表等方式向其他用户提问和交流。
- 实践： 最好的学习方式是实践。通过编写自己的代码，尝试实现各种功能，可以加深对VTK的理解。
3 一个比较有意思的例子
我们模拟一下太阳光线照射到地球上，然后有反射的情况，其实就是一个光线追踪算法。
图2 射线追踪算法
先看代码：
#include <iostream>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkActor.h>
#include <vtkConeSource.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkOBBTree.h>
#include <vtkMath.h>
#include <vtkTransform.h>
#include <vtkTransformFilter.h>
#include <vtkMatrix4x4.h>
#include <vtkPolyDataNormals.h>
#include <vtkPlaneSource.h>
#include <vtkPoints.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkCamera.h>
#include <vtkLight.h>
#include <vtkJPEGReader.h>
#include <vtkTexture.h>
#include <vtkTextureMapToSphere.h>
#include <vtkCellCenters.h>
#include <vtkPolyDataNormals.h>
#include <vtkVertexGlyphFilter.h>
#include <vtkGlyph3D.h>
#include <vtkArrowSource.h>
#include <vtkCellData.h>
#include <vtkPointData.h>
#include <vtkIdList.h>
#include <vtkDoubleArray.h>
#include <vtkLineSource.h>using namespace std;
vtkSmartPointer<vtkActor> point2Actor(vtkSmartPointer<vtkPoints> points){vtkNew<vtkPolyData> polyData;polyData->SetPoints(points);vtkNew<vtkVertexGlyphFilter> filter;filter->SetInputData(polyData);filter->Update();vtkNew<vtkPolyDataMapper> mapper;mapper->SetInputConnection(filter->GetOutputPort());vtkSmartPointer<vtkActor> actor=vtkSmartPointer<vtkActor>::New();actor->SetMapper(mapper);return actor;
}int main()
{// Sun Options// Radius of the sun half-spheredouble RadiusSun=10.0;// Distance of the sun's center from (0,0,0)double DistanceSun=50.0;// Phi & Theta Resolution of sunint ResolutionSun=10;// Earth Options// Radius of the earth spheredouble RadiusEarth=150.0;// Phi & Theta Resolution of earthint ResolutionEarth=120;// Ray Optionsdouble RayCastLength=500.0;// Color Optionsdouble ColorSun[3]={1.0,1.0,0.0};double ColorSunEdge[3]={0.0,0.0,0.0};double ColorEarthEdge[3]={1.0,1.0,1.0};double ColorBackground[]={0.0,0.0,0.0};double ColorLight[]={1.0,1.0,0.0};double ColorSunPoints[]={1.0,1.0,0.0};double ColorSunGlyphs[]={1.0,1.0,0.0};double ColorRayHit[]={1.0,1.0,0.0};double ColorRayMiss[]={1.0,1.0,1.0};double OpacityRayMiss=0.5;double ColorEarthGlyphs[]={0.0,0.0,1.0};double ColorRayReflected[]={1.0,1.0,0.0};// Load a JPEG file with an 'earth' texturevtkNew<vtkJPEGReader> reader;reader->SetFileName("../data/R-C.jpeg");reader->Update();vtkNew<vtkSphereSource> sun;sun->SetCenter(0.0,DistanceSun,0.0);sun->SetRadius(RadiusSun);sun->SetThetaResolution(ResolutionSun);sun->SetPhiResolution(ResolutionSun);sun->SetStartTheta(180); // create a half-sphere// Create mappervtkNew<vtkPolyDataMapper> sunMapper;sunMapper->SetInputConnection(sun->GetOutputPort());// Create actorvtkNew<vtkActor> sunActor;sunActor->SetMapper(sunMapper);sunActor->GetProperty()->SetColor(ColorSun);sunActor->GetProperty()->EdgeVisibilityOn(); // show edges/wireframesunActor->GetProperty()->SetEdgeColor(ColorSunEdge);// Create and configure the earth sperevtkNew<vtkSphereSource> earth;earth->SetCenter(0.0,-RadiusEarth,0.0);earth->SetThetaResolution(ResolutionEarth);earth->SetPhiResolution(ResolutionEarth);earth->SetRadius(RadiusEarth);// texture to earthvtkNew<vtkTexture> texture;texture->SetInputConnection(reader->GetOutputPort());texture->Update();vtkNew<vtkTextureMapToSphere> map_to_sphere;map_to_sphere->SetInputConnection(earth->GetOutputPort());map_to_sphere->PreventSeamOn();map_to_sphere->Update();vtkNew<vtkPolyDataMapper> earthMapper;earthMapper->SetInputConnection(map_to_sphere->GetOutputPort());vtkNew<vtkActor> earthActor;earthActor->SetMapper(earthMapper);earthActor->SetTexture(texture);earthActor->GetProperty()->EdgeVisibilityOn();earthActor->GetProperty()->SetEdgeColor(ColorEarthEdge);// Renderer to displayvtkNew<vtkRenderer> ren;ren->AddActor(sunActor);ren->AddActor(earthActor);ren->SetBackground(ColorBackground);vtkNew<vtkCellCenters> cellCenterCalcSun;cellCenterCalcSun->SetInputConnection(sun->GetOutputPort());cellCenterCalcSun->Update();//cellCenterCalcSun->Print(cout);//cout<<cellCenterCalcSun->GetOutput()->GetNumberOfPoints()<<endl;vtkPoints* pointsInCellCenterCalcSun=cellCenterCalcSun->GetOutput()->GetPoints();/*for(vtkIdType i=0;i<pointsInCellCenterCalcSun->GetNumberOfPoints();++i){double point[3];pointsInCellCenterCalcSun->GetPoint(i,point);cout<<point[0]<<","<<point[1]<<","<<point[2]<<endl;}*/for(vtkIdType i=0;i<cellCenterCalcSun->GetOutput()->GetNumberOfPoints();++i){/*cout<<cellCenterCalcSun->GetOutput()->GetPoint(i)[0]<<","<<cellCenterCalcSun->GetOutput()->GetPoint(i)[1]<<","<<cellCenterCalcSun->GetOutput()->GetPoint(i)[2]<<endl;*/vtkNew<vtkPoints> points;points->InsertNextPoint(cellCenterCalcSun->GetOutput()->GetPoint(i)[0],cellCenterCalcSun->GetOutput()->GetPoint(i)[1],cellCenterCalcSun->GetOutput()->GetPoint(i)[2]);vtkSmartPointer<vtkActor> actor=point2Actor(points);actor->GetProperty()->SetColor(ColorSunPoints);actor->GetProperty()->SetPointSize(5);ren->AddActor(actor);}vtkNew<vtkPolyDataNormals> normalsCalcSun;normalsCalcSun->SetInputConnection(sun->GetOutputPort());// Disable normal calculation at cell verticesnormalsCalcSun->ComputePointNormalsOff();// Enable normal calculation at cell centersnormalsCalcSun->ComputeCellNormalsOn();// Disable splitting of sharp edgesnormalsCalcSun->SplittingOff();// Disable global flipping of normal orientationnormalsCalcSun->FlipNormalsOff();// Enable automatic determination of correct normal orientationnormalsCalcSun->AutoOrientNormalsOn();normalsCalcSun->Update();// Create a 'dummy' vtkCellCenters to force the glyphs to the cell-centersvtkNew<vtkCellCenters> dummy_cellCenterCalcSun;dummy_cellCenterCalcSun->VertexCellsOn();dummy_cellCenterCalcSun->SetInputConnection(normalsCalcSun->GetOutputPort());// Create a new 'default' arrow to use as a glyphvtkNew<vtkArrowSource> arrow;vtkNew<vtkGlyph3D> glyphSun;glyphSun->SetInputConnection(dummy_cellCenterCalcSun->GetOutputPort());glyphSun->SetSourceConnection(arrow->GetOutputPort());glyphSun->SetVectorModeToUseNormal();glyphSun->SetScaleFactor(5);vtkNew<vtkPolyDataMapper> glyphMapperSun;glyphMapperSun->SetInputConnection(glyphSun->GetOutputPort());vtkNew<vtkActor> glyphActorSun;glyphActorSun->SetMapper(glyphMapperSun);glyphActorSun->GetProperty()->SetColor(ColorSunGlyphs);ren->AddActor(glyphActorSun);// Prepare for ray-tracingvtkNew<vtkOBBTree> obbEarth;obbEarth->SetDataSet(earth->GetOutput());obbEarth->BuildLocator();double tol=1.e-8;obbEarth->SetTolerance(tol);vtkNew<vtkPolyDataNormals> normalsCalcEarth;normalsCalcEarth->SetInputConnection(earth->GetOutputPort());normalsCalcEarth->ComputePointNormalsOff();normalsCalcEarth->ComputeCellNormalsOn();normalsCalcEarth->SplittingOff();normalsCalcEarth->FlipNormalsOff();normalsCalcEarth->AutoOrientNormalsOn();normalsCalcEarth->Update();//cout<<"Prepare the ray using point and normal"<<endl;// Extract the normal-vector data at the sun's cellsvtkDataArray* normalsSun=normalsCalcSun->GetOutput()->GetCellData()->GetNormals();// Extract the normal-vector data at the earth's cellsvtkDataArray* normalsEarth=normalsCalcEarth->GetOutput()->GetCellData()->GetNormals();// Create a dummy 'vtkPoints' to act as a container for the point coordinates where intersections are foundvtkNew<vtkPoints> intersectPoints;vtkNew<vtkIdList> intersectCells;// Create a dummy 'vtkList' to act as a container for the normal vectors where intersections are found.vtkNew<vtkDoubleArray> normalsVector;normalsVector->SetNumberOfComponents(3);// Create a dummy 'vtkPolyData' to store points and normalsvtkNew<vtkPoints> dummy_points;vtkNew<vtkPolyData> dummy_polydata;for(vtkIdType i=0;i<pointsInCellCenterCalcSun->GetNumberOfPoints();++i){// Get the coordinates of sun's cell centerdouble pointSun[3];cellCenterCalcSun->GetOutput()->GetPoint(i,pointSun);// Get normal vector at that celldouble* normals=normalsSun->GetTuple(i);//cout<<normals[0]<<","<<normals[1]<<","<<normals[2]<<endl;// Calculate the 'target' of the ray based on 'RayCastLength'double pointEarth[3];pointEarth[0]=pointSun[0]+normals[0]*RayCastLength;pointEarth[1]=pointSun[1]+normals[1]*RayCastLength;pointEarth[2]=pointSun[2]+normals[2]*RayCastLength;int code=obbEarth->IntersectWithLine(pointSun,pointEarth,intersectPoints,intersectCells);if(code<0){continue;}double intersection[3];vtkIdType cellId;double normalIntersect[3];vtkNew<vtkLineSource> line;vtkNew<vtkLineSource> lineRay;for(int i=0;i<intersectPoints->GetNumberOfPoints();++i){if(i==1)continue;intersectPoints->GetPoint(i,intersection);//cout<<"Intersection "<<i<<" : "<<intersection[0]<<","<<intersection[1]<<","<<intersection[2]<<endl;//cellId=intersectCells->GetId(i);//cout<<"\tCellId "<<i<<" : "<<cellId<<endl;normalIntersect[0]=normalsEarth->GetTuple(cellId)[0];normalIntersect[1]=normalsEarth->GetTuple(cellId)[1];normalIntersect[2]=normalsEarth->GetTuple(cellId)[2];normalsVector->InsertNextTuple3(normalIntersect[0],normalIntersect[1],normalIntersect[2]);dummy_points->InsertNextPoint(intersection[0],intersection[1],intersection[2]);// lineline->SetPoint1(pointSun);line->SetPoint2(intersection);// Calculate the incident ray vectordouble vecInc[3];vecInc[0]=intersection[0]-pointSun[0];vecInc[1]=intersection[1]-pointSun[1];vecInc[2]=intersection[2]-pointSun[2];// Calculate reflected ray vectordouble vecRef[3];double dot=vecInc[0]*normalIntersect[0]+vecInc[1]*normalIntersect[1]+vecInc[2]*normalIntersect[2];vecRef[0]=vecInc[0]-2.0*dot*normalIntersect[0];vecRef[1]=vecInc[1]-2.0*dot*normalIntersect[1];vecRef[2]=vecInc[2]-2.0*dot*normalIntersect[2];// Calculate the target of reflected raydouble pointRayReflectedTarget[3];pointRayReflectedTarget[0]=intersection[0]+vecRef[0]*RayCastLength;pointRayReflectedTarget[1]=intersection[1]+vecRef[1]*RayCastLength;pointRayReflectedTarget[2]=intersection[2]+vecRef[2]*RayCastLength;lineRay->SetPoint1(intersection);lineRay->SetPoint2(pointRayReflectedTarget);}vtkNew<vtkPolyDataMapper> lineMapper;vtkNew<vtkPolyDataMapper> lineRayMapper;lineMapper->SetInputConnection(line->GetOutputPort());lineRayMapper->SetInputConnection(lineRay->GetOutputPort());vtkNew<vtkActor> lineActor;vtkNew<vtkActor> lineRayActor;lineActor->SetMapper(lineMapper);lineActor->GetProperty()->SetColor(ColorRayHit);lineRayActor->SetMapper(lineRayMapper);lineRayActor->GetProperty()->SetColor(ColorRayReflected);ren->AddActor(lineActor);ren->AddActor(lineRayActor);}dummy_polydata->SetPoints(dummy_points);dummy_polydata->GetPointData()->SetNormals(normalsVector);vtkNew<vtkGlyph3D> glyphEarth;glyphEarth->SetInputData(dummy_polydata);glyphEarth->SetSourceConnection(arrow->GetOutputPort());glyphEarth->SetVectorModeToUseNormal();glyphEarth->SetScaleFactor(5);vtkNew<vtkPolyDataMapper> glyphMapperEarth;glyphMapperEarth->SetInputConnection(glyphEarth->GetOutputPort());vtkNew<vtkActor> glyphActorEarth;glyphActorEarth->SetMapper(glyphMapperEarth);glyphActorEarth->GetProperty()->SetColor(ColorEarthGlyphs);ren->AddActor(glyphActorEarth);vtkNew<vtkCamera> camera;camera->SetPosition(RadiusEarth,DistanceSun,RadiusEarth);camera->SetFocalPoint(0.0,0.0,0.0);camera->SetViewAngle(30.0);ren->SetActiveCamera(camera);//vtkNew<vtkRenderWindow> renWin;renWin->SetSize(1024,1024);renWin->AddRenderer(ren);vtkNew<vtkRenderWindowInteractor> iren;iren->SetRenderWindow(renWin);vtkNew<vtkInteractorStyleTrackballCamera> style;iren->SetInteractorStyle(style);iren->Initialize();iren->Start();return 0;
}在代码中有详细的说明，等有空我会讲解一下。