等值面（线）
抽取轮廓的操作对象是标量数据。其思想是：将数据集中标量值等于某一指定恒量值的部分提取出来。对于3D的数据集而言，产生的是一个等值面；对于2D的数据集而言，产生的是一个等值线。其典型的应用有气象图中的等温线、地形图中的等高线。对于医学数据而言，不同的标量值代表的是人体的不同部分，因而可以分别提取出人的皮肤或骨头。 抽取轮廓的功能是由一个过滤器实现的，如vtkContourFilter 。vtkContourFilter 可以接受任意数据集类型作为输入，因而具有 一般性。使用vtkContourFilter 时，除了需要设置输入数据集外，还需要指定一个或多个用于抽取的标量值。可用如下两种方法进行设置。
使用方法SetValue()逐个设置抽取值。该方法有个两个参数：第一个参数是抽取值的索引号，表示第几个 抽取值。索引号从0开始计数；第二个参数就是指定的抽取值。使用方法GenerateValues()自动产生一系列抽取值。该方法有三个参数：第一个参数是抽取值的个数，后面两个参数是抽取值的取值范围。例如：
vtkSmartPointer<vtkContourFilter> contours = vtkSmartPointer<vtkContourFilter>::New();
contours->GenerateValues(5.0, 0.0, 1.2);
最终产生的抽取值为0.0， 0.3， 0.6， 0.9和1.0，这是一个等差数列。
vtkContourFilter生成等值线示例
CMakeLists.txt文件代码如下：
CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
PROJECT(Contour)
FIND_PACKAGE(VTK REQUIRED)
INCLUDE(${VTK_USE_FILE})
ADD_EXECUTABLE(Contour Contour.cpp)
TARGET_LINK_LIBRARIES(Contour ${VTK_LIBRARIES})
Contour.cpp文件代码如下：
#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkCellArray.h>
#include <vtkFloatArray.h>
#include <vtkPointData.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkLookupTable.h>
#include <vtkContourFilter.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkProperty.h>
#include <vtkSmartPointer.h>
int main()
{
int i;
//定义网格的顶点坐标
vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
//第1行5个点
points->InsertNextPoint(-2.0, 2.0, 0.0);
points->InsertNextPoint(-1.0, 2.0, 0.0);
points->InsertNextPoint(0.0, 2.0, 0.0);
points->InsertNextPoint(1.0, 2.0, 0.0);
points->InsertNextPoint(2.0, 2.0, 0.0);
//第2行5个点
points->InsertNextPoint(-2.0, 1.0, 0.0);
points->InsertNextPoint(-1.0, 1.0, 0.0);
points->InsertNextPoint(0.0, 1.0, 0.0);
points->InsertNextPoint(1.0, 1.0, 0.0);
points->InsertNextPoint(2.0, 1.0, 0.0);
//第3行5个点
points->InsertNextPoint(-2.0, 0.0, 0.0);
points->InsertNextPoint(-1.0, 0.0, 0.0);
points->InsertNextPoint(0.0, 0.0, 0.0);
points->InsertNextPoint(1.0, 0.0, 0.0);
points->InsertNextPoint(2.0, 0.0, 0.0);
//第4行5个点
points->InsertNextPoint(-2.0, -1.0, 0.0);
points->InsertNextPoint(-1.0, -1.0, 0.0);
points->InsertNextPoint(0.0, -1.0, 0.0);
points->InsertNextPoint(1.0, -1.0, 0.0);
points->InsertNextPoint(2.0, -1.0, 0.0);
//第5行5个点
points->InsertNextPoint(-2.0, -2.0, 0.0);
points->InsertNextPoint(-1.0, -2.0, 0.0);
points->InsertNextPoint(0.0, -2.0, 0.0);
points->InsertNextPoint(1.0, -2.0, 0.0);
points->InsertNextPoint(2.0, -2.0, 0.0);
//定义单元，每个顶点建立一个四边形单元，共计个单元
static vtkIdType pts[16][4] = { { 0, 5, 6, 1 }, { 1, 6, 7, 2 }, { 2, 7, 8, 3 },
{ 3, 8, 9, 4 }, { 5, 10, 11, 6 }, { 6, 11, 12, 7 }, { 7, 12, 13, 8 }, { 8, 13, 14, 9 },
{ 10, 15, 16, 11 }, { 11, 16, 17, 12 }, { 12, 17, 18, 13 }, { 13, 18, 19, 14 },
{ 15, 20, 21, 16 }, { 16, 21, 22, 17 }, { 17, 22, 23, 18 }, { 18, 23, 24, 19 } };
//创建对象
vtkSmartPointer<vtkPolyData> pGrid = vtkSmartPointer<vtkPolyData>::New();
vtkSmartPointer<vtkCellArray> polys = vtkSmartPointer<vtkCellArray>::New();
for (i = 0; i < 16; i++)
{
polys->InsertNextCell(4, pts[i]);
}
vtkSmartPointer<vtkFloatArray> scalars = vtkSmartPointer<vtkFloatArray>::New();
//第1行
scalars->InsertTuple1(0, 0);
scalars->InsertTuple1(1, 1);
scalars->InsertTuple1(2, 1);
scalars->InsertTuple1(3, 3);
scalars->InsertTuple1(4, 2);
//第2行
scalars->InsertTuple1(5, 1);
scalars->InsertTuple1(6, 3);
scalars->InsertTuple1(7, 6);
scalars->InsertTuple1(8, 6);
scalars->InsertTuple1(9, 3);
//第3行
scalars->InsertTuple1(10, 3);
scalars->InsertTuple1(11, 7);
scalars->InsertTuple1(12, 9);
scalars->InsertTuple1(13, 7);
scalars->InsertTuple1(14, 3);
//第4行
scalars->InsertTuple1(15, 2);
scalars->InsertTuple1(16, 7);
scalars->InsertTuple1(17, 8);
scalars->InsertTuple1(18, 6);
scalars->InsertTuple1(19, 2);
//第5行
scalars->InsertTuple1(20, 1);
scalars->InsertTuple1(21, 2);
scalars->InsertTuple1(22, 3);
scalars->InsertTuple1(23, 4);
scalars->InsertTuple1(24, 3);
pGrid->SetPoints(points);
pGrid->SetPolys(polys);
pGrid->GetPointData()->SetScalars(scalars);
//定义颜色映射表
vtkSmartPointer<vtkLookupTable> pColorTable = vtkSmartPointer<vtkLookupTable>::New();
pColorTable->SetHueRange(0.667, 0.887);
pColorTable->SetNumberOfColors(255);
pColorTable->Build();
vtkSmartPointer<vtkPolyDataMapper> cubeMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
cubeMapper->SetInputData(pGrid);
cubeMapper->SetScalarRange(0, 9);
cubeMapper->SetLookupTable(pColorTable);
vtkSmartPointer<vtkActor> cubeActor = vtkSmartPointer<vtkActor>::New();
cubeActor->SetMapper(cubeMapper);
//提取轮廓线
vtkSmartPointer<vtkContourFilter> pContourFilter = vtkSmartPointer<vtkContourFilter>::New();
pContourFilter->SetValue(0, 5.0);
pContourFilter->SetInputData(pGrid);
pContourFilter->Update();
vtkSmartPointer<vtkPolyDataMapper> pContourMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
pContourMapper->SetInputData(pContourFilter->GetOutput());
pContourMapper->ScalarVisibilityOff();
vtkSmartPointer<vtkActor> pContourActor = vtkSmartPointer<vtkActor>::New();
pContourActor->SetMapper(pContourMapper);
pContourActor->GetProperty()->SetColor(1.0, 1.0, 0.0);
pContourActor->GetProperty()->SetLineWidth(5.0);
vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
renderer->AddActor(pContourActor);
renderer->AddActor(cubeActor);
renderer->SetBackground(1.0, 1.0, 1.0);
vtkSmartPointer<vtkRenderWindow> renWin = vtkSmartPointer<vtkRenderWindow>::New();
renWin->SetSize(300, 300);
renWin->AddRenderer(renderer);
renWin->SetWindowName("vtkContourFilter");
vtkSmartPointer<vtkRenderWindowInteractor> interactor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
interactor->SetRenderWindow(renWin);
interactor->Initialize();
interactor->Start();
}
运行结果
示例原理
定义规则网格数据顶点的属性值，示例中设置标量值。确定提取区域的属性值。用提取区域的属性值和每个网格数据的每个单元进行比对，确定其是否在该单元内，如果在该单元内，要用插值的方法确定其和该单元边界的交点，然后继续比对下一个单元，如果不在该单元内，继续比对下一个单元。将各个单元的交点相连成线，即为边界区域。 ##原理示意图：
