vtkCutter Find The Intersections Between Bounding Box Plane And Polydata

Create a simple cone and plane.

#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 <vtkLight.h>
#include <vtkCamera.h>
#include <vtkOBBTree.h>
#include <vtkActor2D.h>
#include <vtkMath.h>
#include <vtkTransform.h>
#include <vtkTransformFilter.h>
#include <vtkMatrix4x4.h>
#include <vtkInteractorObserver.h>
#include <vtkPolyDataNormals.h>
#include <vtkOutlineFilter.h>
#include <vtkPlaneSource.h>

#include "tool.h"

using namespace std;

int main()
{
    setbuf( stdout, nullptr );
    vtkSmartPointer<vtkPlaneSource> planeSource =
            vtkSmartPointer<vtkPlaneSource>::New();
    planeSource->SetCenter( -0.5, 0, 0 );
    planeSource->SetNormal( 1, 0, 0 );
    planeSource->Update();

    vtkSmartPointer<vtkPolyDataMapper> planeMapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
    planeMapper->SetInputData( planeSource->GetOutput() );
    planeMapper->Update();

    vtkSmartPointer<vtkActor> planeActor =
            vtkSmartPointer<vtkActor>::New();
    planeActor->SetMapper( planeMapper );
    planeActor->GetProperty()->SetColor( 0, 1, 0 );

    vtkSmartPointer<vtkConeSource> cone =
            vtkSmartPointer<vtkConeSource>::New();
    //cone->SetDirection( 1, 1, 0 );
    cone->Update();

    PointStruct center, max, mid, min, size;
    vtkSmartPointer<vtkOBBTree> obbTree =
            vtkSmartPointer<vtkOBBTree>::New();
    obbTree->ComputeOBB( cone->GetOutput(),
                         center.point,
                         max.point,
                         mid.point,
                         min.point,
                         size.point );

    vtkMath::Normalize( center.point );
    vtkMath::Normalize( max.point );
    vtkMath::Normalize( mid.point );
    vtkMath::Normalize( min.point );

    cout << "center: " << center;
    cout << "max: " << max;
    cout << "mid: " << mid;
    cout << "min: " << min;

    vtkSmartPointer<vtkPolyDataMapper> mapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
    mapper->SetInputData( cone->GetOutput() );

    vtkSmartPointer<vtkActor> actor =
            vtkSmartPointer<vtkActor>::New();
    actor->SetMapper( mapper );

    vtkSmartPointer<vtkRenderer> renderer =
            vtkSmartPointer<vtkRenderer>::New();
    renderer->AddActor(actor);
    renderer->AddActor(planeActor);
    renderer->SetBackground( 0, 0, 0 );

    vtkSmartPointer<vtkRenderWindow> renderWindow =
            vtkSmartPointer<vtkRenderWindow>::New();
    renderWindow->AddRenderer( renderer );

    vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
            vtkSmartPointer<vtkRenderWindowInteractor>::New();
    renderWindowInteractor->GetInteractorStyle()->SetCurrentRenderer( renderer );
    renderWindowInteractor->SetRenderWindow( renderWindow );

    renderer->ResetCamera();
    renderWindow->Render();
    renderWindowInteractor->Start();
    return 0;
}

Rotate cone, make cone->SetDirection( 1, 1, 0 ); works.

Use bounding box point to set plane at left side.

   double boundingBox[6] = { 0 };
    cone->GetOutput()->GetBounds( boundingBox );
    PointStruct pt0( boundingBox[0], boundingBox[3], boundingBox[5] );
    PointStruct pt1( boundingBox[0], boundingBox[3], boundingBox[4] );
    PointStruct pt2( boundingBox[0], boundingBox[2], boundingBox[4] );
    PointStruct centerPt = pt0 + pt2;
    centerPt /= 2;

    vtkSmartPointer<vtkPlaneSource> planeSource =
            vtkSmartPointer<vtkPlaneSource>::New();
    //planeSource->SetPoint1( (pt1 - pt0).point );
    //planeSource->SetPoint2( (pt2 - pt0).point );

    planeSource->SetCenter( centerPt.point );
    planeSource->SetNormal( 1, 0, 0 );
    planeSource->Update();

    vtkSmartPointer<vtkPolyDataMapper> planeMapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
    planeMapper->SetInputData( planeSource->GetOutput() );
    planeMapper->Update();

    vtkSmartPointer<vtkActor> planeActor =
            vtkSmartPointer<vtkActor>::New();
    planeActor->SetMapper( planeMapper );
    planeActor->GetProperty()->SetColor( 0, 1, 0 );

How to find the intersections point between plane and cone?
vtkCutter can help us to find all intersections.

    // Create cutter
    vtkSmartPointer<vtkCutter> cutter =
      vtkSmartPointer<vtkCutter>::New();
    cutter->SetCutFunction( planeFunction );
    cutter->SetInputData( cone->GetOutput() );
    cutter->Update();

    cout << "Cutter GetNumberOfPoints: " << cutter->GetOutput()->GetNumberOfPoints() << endl;
    vtkSmartPointer<vtkPolyDataMapper> cutterMapper =
      vtkSmartPointer<vtkPolyDataMapper>::New();
    cutterMapper->SetInputData( cutter->GetOutput() );

    vtkSmartPointer<vtkActor> cutterActor =
            vtkSmartPointer<vtkActor>::New();
    cutterActor->SetMapper( cutterMapper );
    cutterActor->GetProperty()->SetColor( 1, 0, 0 );
 ```

If we put a plane on the bounding box, it can’t find the intersection.
So we should move the plane a little closer.

```cpp
    vtkSmartPointer<vtkPlaneSource> planeSource =
            vtkSmartPointer<vtkPlaneSource>::New();
    centerPt[0] = centerPt[0] + 0.01; //move it
    planeSource->SetCenter( centerPt.point );
    planeSource->SetNormal( 1, 0, 0 );
    planeSource->Update();

Output:

Cutter GetNumberOfPoints: 4

Look it at wireframe representation.