Convert Length Between Coordinate System, Rotate Vector, And Mark Position

The article shows a few tips in VTK development. There are simple tasks for most developers but the functions can be used in many situations.

Convert the length value in the display coordinate system to the new value in the world coordinate system.

double DisplayLenToWorldLen(const double &length)
{
    Point p0( 0, 0, 0 );
    vtkRenderer *renderer = GetVtkRenderer();
    renderer->SetDisplayPoint( p0.point );
    renderer->DisplayToWorld();
    double tmp[4];
    renderer->GetWorldPoint( tmp );
    Point worldP0( tmp[0], tmp[1], tmp[2] );

    Point p1( length, 0, 0 );
    renderer->SetDisplayPoint( p1.point );
    renderer->DisplayToWorld();
    renderer->GetWorldPoint( tmp );
    Point worldP1( tmp[0], tmp[1], tmp[2] );

    return (worldP0 - worldP1).Length();
}

Rotate a vector to the target direction.

    // Rotate Y to be plane normal
    PointStruct planeNormal = GetPlaneNormal();
    planeNormal.Unit();
    PointStruct YDir( 0, 1, 0 );
    PointStruct rotateAxis = YDir ^ planeNormal;
    double radians = vtkMath::AngleBetweenVectors( YDir.point, planeNormal.point );
    double angle = vtkMath::DegreesFromRadians( radians );
    userTransform->Translate( center.point );  // center is our rotate center.
    userTransform->RotateWXYZ( angle, rotateAxis.point );
    userTransform->Translate( (-center).point );
    userTransform->Update();

Show a sphere at the special position. It’s often used as a debug function.

void ShowPoint( Point pt, vtkRenderer *renderer )
{
    vtkSmartPointer<vtkSphereSource> sphere =
        vtkSmartPointer<vtkSphereSource>::New();
    sphere->SetThetaResolution( 100 );
    sphere->SetPhiResolution( 50 );
    sphere->SetRadius( 1 );
    sphere->SetCenter( pt.point );
    sphere->Update();

    vtkSmartPointer<vtkPolyDataMapper> sphereMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
    sphereMapper->SetInputData( sphere->GetOutput() );

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

    renderer->AddActor( actor );
}