VTK-vtkBandedPolyDataContourFilter学习

官网有一个例子，看完之后仍然不太明白。经过一点点的探索，记录一下收获。

1.建立一个六边形的点集

Create(vtkPoints, points);
    points->InsertNextPoint(-5, 0, 0);
    points->InsertNextPoint(-2.5, -4.33, 0);
    points->InsertNextPoint(2.5, -4.33, 0);
    points->InsertNextPoint(5, 0, 0);
    points->InsertNextPoint(2.5, 4.33, 0);
    points->InsertNextPoint(-2.5, 4.33, 0);

2.创建单元结构

Create(vtkCellArray, cells);
    cells->InsertNextCell(6);
    cells->InsertCellPoint(0);
    cells->InsertCellPoint(1);
    cells->InsertCellPoint(2);
    cells->InsertCellPoint(3);
    cells->InsertCellPoint(4);
    cells->InsertCellPoint(5);

3.分配一个标量数据

Create(vtkFloatArray, scalars);
    scalars->InsertNextValue(50);
    scalars->InsertNextValue(50);
    scalars->InsertNextValue(150);
    scalars->InsertNextValue(200);
    scalars->InsertNextValue(200);
    scalars->InsertNextValue(150);

顶点上的标量数据如图所示。为了帮助理解，所以数据分配的比较整齐。

4.用上面的数据创建Polydata

Create(vtkPolyData, polydata);
    polydata->SetPoints(points);
    polydata->SetPolys(cells);
    polydata->GetPointData()->SetScalars(scalars);

 5.vtkBandedPolyDataContourFilter等值线

Create(vtkBandedPolyDataContourFilter, bandeds);
    bandeds->SetInputData(polydata);
    bandeds->GenerateValues(5, 75, 175);
    bandeds->Update();

这里的作用是将点标量数据重新划分，生成等值线。

GenerateValues(5, 75, 175)这句话将75-175这个范围划分成4段（5点），会生成下面的等值：

75，100，125，150，175

这样一看非常清晰,这个过滤器从点标量数据生成单元标量数据。 

6.显示条带

Create(vtkPolyDataMapper, mapper);
    mapper->SetInputConnection(bandeds->GetOutputPort());
    mapper->SetScalarModeToUseCellData();
    mapper->SetScalarRange(bandeds->GetOutput()->GetCellData()->GetScalars()->GetRange());

标量模式一定要是cellData,而且标量范围是上面的过滤生成的单元标量范围，也可以手动输入范围，范围外的标量数据就自动取极值了。

7.完整代码

#include<vtkBandedPolyDataContourFilter.h>

#include"vtkFloatArray.h"

#include"vtkModelInit.h"
#include"vtkGloble.h"


int main()
{
    Create(vtkPoints, points);
    points->InsertNextPoint(-5, 0, 0);
    points->InsertNextPoint(-2.5, -4.33, 0);
    points->InsertNextPoint(2.5, -4.33, 0);
    points->InsertNextPoint(5, 0, 0);
    points->InsertNextPoint(2.5, 4.33, 0);
    points->InsertNextPoint(-2.5, 4.33, 0);


    Create(vtkCellArray, cells);
    cells->InsertNextCell(6);
    cells->InsertCellPoint(0);
    cells->InsertCellPoint(1);
    cells->InsertCellPoint(2);
    cells->InsertCellPoint(3);
    cells->InsertCellPoint(4);
    cells->InsertCellPoint(5);

    Create(vtkFloatArray, scalars);
    scalars->InsertNextValue(50);
    scalars->InsertNextValue(50);
    scalars->InsertNextValue(150);
    scalars->InsertNextValue(200);
    scalars->InsertNextValue(200);
    scalars->InsertNextValue(150);

    Create(vtkPolyData, polydata);
    polydata->SetPoints(points);
    polydata->SetPolys(cells);
    polydata->GetPointData()->SetScalars(scalars);


    Create(vtkBandedPolyDataContourFilter, bandeds);
    bandeds->SetInputData(polydata);
    bandeds->GenerateValues(5, 75, 175);
    bandeds->Update();

    Create(vtkPolyDataMapper, mapper);
    mapper->SetInputConnection(bandeds->GetOutputPort());
    mapper->SetScalarModeToUseCellData();
    mapper->SetScalarRange(bandeds->GetOutput()->GetCellData()->GetScalars()->GetRange());


    Create(vtkActor, actor);
    actor->SetMapper(mapper);
    Create(vtkRenderer, render);
    render->AddActor(actor);
    Create(vtkRenderWindow, window);
    window->AddRenderer(render);
    Create(vtkRenderWindowInteractor, inter);
    inter->SetRenderWindow(window);


    inter->Start();
    return 0;
}