什么是包围盒
包围盒是指能够包容物体的立方体或者二维长方形，是包围体的一种，常常用于模型的碰撞检测。包围体主要包括球体、轴对齐包围盒(AABB)、有向包围盒(OBB)和凸包(Convex Hull)。
在较早的时候，包围盒按照坐标系的坐标轴进行排列，这被称为轴对齐的包围盒(AABB/Axis-aligned bounding box)。为了将AABB与通用的情况区分开来，将任意的包围盒称为有向包围盒(OBB/Oriented bounding box)。AABB检测模型的相交要比OBB更简单，但是他的缺点是当模型旋转的时候无法随之旋转，而必须重新计算。
轴对齐包围盒
在VTK中，轴对齐包围盒被定义为包含该模型，且边平行于坐标轴的最小六面体。AABB比较简单，存储空间小，仅需六个标量。
获取的标量也很简单，vtkPolyData中定义了GetBounds()函数，用来获取包围盒的参数，即三个轴向上的最大值和最小值。
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| vtkSmartPointer<vtkPolyData> polydata =
vtkSmartPointer<vtkPolyData>::New();
double bounds[6];
polydata->GetBounds(bounds);
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需要注意的是，通过reader或者source来的模型，需要先Update()；
而有时候仅仅是获取这些参数并不直观，还需要
显示包围盒，vtkOutlineFilter提供了这一方便的操作，输入模型的数据，就很容易的可视化显示。
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| vtkSmartPointer<vtkOutlineFilter> outline =
vtkSmartPointer<vtkOutlineFilter>::New();
outline->SetInputData(polydata);
outline->Update();
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Default Solid face is off, on:
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| outline->GenerateFacesOn();
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效果
示例代码
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| #include <vtkSmartPointer.h>
#include <vtkPolyData.h>
#include <vtkSphereSource.h>
#include <vtkXMLPolyDataReader.h>
#include <vtkActor.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkOutlineFilter.h>
#include <vtkProperty.h>
int main(int argc, char *argv[])
{
vtkSmartPointer<vtkPolyData> polydata =
vtkSmartPointer<vtkPolyData>::New();
if (argc > 1)
{
vtkSmartPointer<vtkXMLPolyDataReader> reader =
vtkSmartPointer<vtkXMLPolyDataReader>::New();
reader->SetFileName(argv[1]);
reader->Update();
polydata = reader->GetOutput();
}
else
{
vtkSmartPointer<vtkSphereSource> modelSource =
vtkSmartPointer<vtkSphereSource>::New();
modelSource->Update();
polydata = modelSource->GetOutput();
}
vtkSmartPointer<vtkOutlineFilter> outline =
vtkSmartPointer<vtkOutlineFilter>::New();
outline->SetInputData(polydata);
outline->Update();
double bounds[6];
polydata->GetBounds(bounds);
std::cout << "Polydata bounds: " << std::endl;
std::cout << "xmin: " << bounds[0] << " "
<< "xmax: " << bounds[1] << std::endl
<< "ymin: " << bounds[2] << " "
<< "ymax: " << bounds[3] << std::endl
<< "zmin: " << bounds[4] << " "
<< "zmax: " << bounds[5] << std::endl;
outline->GetOutput()->GetBounds(bounds);
std::cout << "Outline bounds: " << std::endl;
std::cout << "xmin: " << bounds[0] << " "
<< "xmax: " << bounds[1] << std::endl
<< "ymin: " << bounds[2] << " "
<< "ymax: " << bounds[3] << std::endl
<< "zmin: " << bounds[4] << " "
<< "zmax: " << bounds[5] << std::endl;
vtkSmartPointer<vtkPolyDataMapper> modelMapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
modelMapper->SetInputData(polydata);
vtkSmartPointer<vtkActor> modelActor =
vtkSmartPointer<vtkActor>::New();
modelActor->SetMapper(modelMapper);
vtkSmartPointer<vtkPolyDataMapper> outlineMapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
outlineMapper->SetInputConnection(outline->GetOutputPort());
vtkSmartPointer<vtkActor> outlineActor =
vtkSmartPointer<vtkActor>::New();
outlineActor->SetMapper(outlineMapper);
outlineActor->GetProperty()->SetColor(1, 0, 0);
outlineActor->GetProperty()->SetLineWidth(1.5);
vtkSmartPointer<vtkRenderer> renderer =
vtkSmartPointer<vtkRenderer>::New();
vtkSmartPointer<vtkRenderWindow> renderWindow =
vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->SetSize(300, 300);
renderWindow->AddRenderer(renderer);
vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
renderWindowInteractor->SetRenderWindow(renderWindow);
renderer->AddActor(modelActor);
renderer->AddActor(outlineActor);
renderWindow->Render();
renderWindowInteractor->Start();
return EXIT_SUCCESS;
}
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Ref
维基百科.包围体
VTK/Examples/Cxx/PolyData/DataBounds
