??使用vtk来绘制等值线，需要使用到vtkContourFilter，它所处理的数据需要是规则网格数据，如规则的正方形网格等。
??通过使用vtkContourFilter::SetValue(i,value)方法，i表示第几条等值线，从0开始计算，value表示等值线的值。多边形的每个点都有一个属性值，两个相邻的属性值之间要先通过插值，再把这些属性值作为该函数的输入。如：
????????????SetValue(0,5);
画一条等值为5的等值线。两个相邻的点的属性值为3和6，则先插值为（3,4,5,6），所以该先应该经过这条边的2/3处。
??也可以使用vtkContourFilter：：GenerateValues(count, start, end);来生成一些列的等值线，其中count参数指定等值线的条数，而start指定第一条等值线的值，end指定最后一条等值线的值，中间等值线的值则通过计算得到。
????vtkContourFilter::SetValue(…)、GenerateValues(…)、GetNumberOfContours(…)
解释：
??SetValue和GenerateValues均为设置等值线值的函数；这两个函数的不同之处在于SetValue设置一条等值线值，而GenerateValues对应n条等值线的值，同时数量n包括两个边界值，其余n-2条等值线的值自动按照线性关系产生。
??SetValue和GenerateValues函数根据先后调用关系产生覆盖，即后调用的函数产生的等值线可能覆盖掉先调用函数产生的等值线，这与等值线的条数(GetNumberOfContours)相关。
??例如：首先调用GenerateValues(3, 100, 300)产生3条等值线，分别为100、200、300；然后调用SetValue(0, 125)，则最终效果为共有3条等值线，分别为125、200、300；如果改为调用SetValue(3, 400)，则最终效果为共有4条等值线，分别为100、200、300、400。
??SetValue一般用于覆盖某一条已经存在的等值线，或者增加一条等值线；GenerateValues一般重新设置等值线的条数。
示例代码：
#include "vtkAutoInit.h"
VTK_MODULE_INIT( vtkRenderingOpenGL2 );
VTK_MODULE_INIT( vtkInteractionStyle );
#include "vtkSmartPointer.h"
#include "vtkContourFilter.h"
#include "vtkInteractorStyleUser.h"
#include "vtkProperty.h"
#include "vtkOutlineFilter.h"
#include "vtkCommand.h"
#include "vtkSliderWidget.h"
#include "vtkSliderRepresentation.h"
#include "vtkSliderRepresentation3D.h"
#include "vtkImageData.h"
#include "vtkCellArray.h"
#include "vtkFloatArray.h"
#include "vtkPointData.h"
#include "vtkPolyDataMapper.h"
#include "vtkActor.h"
#include "vtkRenderer.h"
#include "vtkRenderWindow.h"
#include "vtkRenderWindowInteractor.h"
#include "vtkXMLImageDataWriter.h"
#include "vtkNamedColors.h"
namespace
{void CreateData( vtkImageData* data );
class vtkSliderCallback : public vtkCommand
{
public:
static vtkSliderCallback* New()
{
return new vtkSliderCallback;
}
virtual void Execute( vtkObject *caller, unsigned long eventId, void *callData )
{
vtkSliderWidget* sliderWidget = reinterpret_cast<vtkSliderWidget*>(caller);
double value = static_cast<vtkSliderRepresentation*>(sliderWidget->GetRepresentation())->GetValue();
this->ContourFilter->GenerateValues( 5, 10.0, value );
//5: 5contour line
//10.0 * value: start value
//value: end value
}
vtkSliderCallback() : ContourFilter( NULL ){}
vtkContourFilter* ContourFilter;
};}
int main()
{
vtkSmartPointer<vtkNamedColors> colors = vtkSmartPointer<vtkNamedColors>::New();
vtkSmartPointer<vtkImageData> imgData = vtkSmartPointer<vtkImageData>::New();
CreateData( imgData );
//Create an iso surface
vtkSmartPointer<vtkContourFilter> contourFilter = vtkSmartPointer<vtkContourFilter>::New();
contourFilter->SetInputData( imgData );
contourFilter->GenerateValues( 5, 10, 10 );
//Map the contours to graphical primitives
vtkSmartPointer<vtkPolyDataMapper> contourMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
contourMapper->SetInputConnection( contourFilter->GetOutputPort() );
//Create an actor for the contours
vtkSmartPointer<vtkActor> contourActor = vtkSmartPointer<vtkActor>::New();
contourActor->SetMapper( contourMapper );
contourActor->GetProperty()->SetLineWidth( 5 );
//Create the outline
vtkSmartPointer<vtkOutlineFilter> outlineFilter = vtkSmartPointer<vtkOutlineFilter>::New();
outlineFilter->SetInputData( imgData );
vtkSmartPointer<vtkPolyDataMapper> outlineMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
outlineMapper->SetInputConnection( outlineFilter->GetOutputPort() );
vtkSmartPointer<vtkActor> outlineActor = vtkSmartPointer<vtkActor>::New();
outlineActor->SetMapper( outlineMapper );
outlineActor->GetProperty()->SetColor( colors->GetColor3d( "Gray" ).GetData() );
outlineActor->GetProperty()->SetLineWidth( 3 );
//Visualize
vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->AddRenderer( renderer );
vtkSmartPointer<vtkRenderWindowInteractor> interactor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
interactor->SetRenderWindow( renderWindow );
renderer->AddActor( contourActor );
renderer->AddActor( outlineActor );
renderer->SetBackground( colors->GetColor3d( "Burlywood" ).GetData() );
vtkSmartPointer<vtkSliderRepresentation3D> sliderRep = vtkSmartPointer<vtkSliderRepresentation3D>::New();
sliderRep->SetMinimumValue( 0.0 );
sliderRep->SetMaximumValue( 30.0 );
sliderRep->SetValue( 10.0 );
sliderRep->SetTitleText( "Contour value" );
sliderRep->SetPoint1InWorldCoordinates( -20, -40, 0 );
sliderRep->SetPoint2InWorldCoordinates( 0, -40, 0 );
sliderRep->SetSliderWidth( 0.2 );
sliderRep->SetLabelHeight( 0.1 );
vtkSmartPointer<vtkSliderWidget> sliderWidget = vtkSmartPointer<vtkSliderWidget>::New();
sliderWidget->SetInteractor( interactor );
sliderWidget->SetRepresentation( sliderRep );
sliderWidget->SetAnimationModeToAnimate();
sliderWidget->EnabledOn();
vtkSmartPointer<vtkSliderCallback> callback = vtkSmartPointer<vtkSliderCallback>::New();
callback->ContourFilter = contourFilter;
sliderWidget->AddObserver( vtkCommand::InteractionEvent, callback );
vtkSmartPointer<vtkInteractorStyleUser> interactStyle = vtkSmartPointer<vtkInteractorStyleUser>::New();
interactor->SetInteractorStyle( interactStyle );
renderWindow->SetSize( 500, 500 );
renderWindow->Render();
interactor->Start();
return EXIT_SUCCESS;}
namespace
{
void CreateData( vtkImageData* pData )
{
pData->SetExtent( -25, 25, -25, 25, 0, 0 );
pData->AllocateScalars( VTK_DOUBLE, 1 );
int* extent = pData->GetExtent(); for( int y = extent[ 2 ]; y <= extent[ 3 ]; y++ )
{
for( int x = extent[ 0 ]; x <= extent[ 1 ]; x++ )
{
double* pixel = static_cast<double*>(pData->GetScalarPointer( x, y, 0 ));
pixel[ 0 ] = sqrt( pow( x, 2.0 ) + pow( y, 2.0 ) );
}
}
vtkSmartPointer<vtkXMLImageDataWriter> writer =
vtkSmartPointer<vtkXMLImageDataWriter>::New();
writer->SetFileName( "data.vti" );
writer->SetInputData( pData );
writer->Write();
writer->Update();
}}
结果如下图所示：
原文地址：http://blog.51cto.com/weiyuqingcheng/2113496
