[vtkusers] Picking Pixel

[Xiaopeng Yang]

Hello,

 

Attached is part of the PickingAPixel example which can get the world
coordinates of the pick. However, I would like to know the index coordinates
too. So how to modify the code to get the index coordinates?

 

Thanks a lot,

Xiaopeng

 

// The mouse motion callback, to pick the image and recover pixel values

class vtkImageInteractionCallback1 : public vtkCommand

{

public:

 

  static vtkImageInteractionCallback1 *New() 

    {

    return new vtkImageInteractionCallback1; 

    }

 

  vtkImageInteractionCallback1() 

    {

    this->Viewer = 0;

    this->Picker = 0;

    this->Annotation = 0;

    this->PointData = vtkPointData::New();

    }

 

  ~vtkImageInteractionCallback1()

     {

     this->Viewer = 0;

     this->Picker = 0;

     this->Annotation = 0;

     this->PointData->Delete();

     }

 

  void SetPicker(vtkPropPicker *picker) 

    {

    this->Picker = picker; 

    }

 

  void SetAnnotation(vtkCornerAnnotation *annotation) 

    {

    this->Annotation = annotation; 

    }

 

  void SetViewer(vtkImageViewer2 *viewer) 

    {

    this->Viewer = viewer; 

    }

 

    virtual void Execute(vtkObject *, unsigned long vtkNotUsed(event), void
*)

      {

      //this->Viewer;

      vtkRenderWindowInteractor *interactor =

        this->Viewer->GetRenderWindow()->GetInteractor();

      vtkRenderer* renderer = this->Viewer->GetRenderer();

      vtkImageActor* actor = this->Viewer->GetImageActor();

      vtkImageData* image = this->Viewer->GetInput();

      vtkInteractorStyle *style = vtkInteractorStyle::SafeDownCast(

          interactor->GetInteractorStyle());

 

      image->Update();

 

      // Pick at the mouse location provided by the interactor

      this->Picker->Pick( interactor->GetEventPosition()[0],

                          interactor->GetEventPosition()[1],

                          0.0, renderer );

 

      // There could be other props assigned to this picker, so 

      // make sure we picked the image actor

      vtkAssemblyPath* path = this->Picker->GetPath();

      bool validPick = false;

 

      if( path )

        {

        vtkCollectionSimpleIterator sit;

        path->InitTraversal( sit );

        vtkAssemblyNode *node;

        for( int i = 0; i < path->GetNumberOfItems() && !validPick; ++i )

          {

          node = path->GetNextNode( sit );

          if( actor == vtkImageActor::SafeDownCast( node->GetViewProp() ) )

            {

            validPick = true;

            }

          }

        }

 

      if( !validPick )

        {

        this->Annotation->SetText( 0, "Off Image" );

        interactor->Render();

        // Pass the event further on

        style->OnMouseMove();

        return;

        }

 

      // Get the world coordinates of the pick

      double pos[3];

      this->Picker->GetPickPosition( pos );

      // Fixes some numerical problems with the picking

      double *bounds = actor->GetDisplayBounds();

      int axis = this->Viewer->GetSliceOrientation();

      pos[axis] = bounds[2*axis];

 

      vtkPointData* pd = image->GetPointData();

      if( !pd )

        {

        return;

        }

 

      this->PointData->InterpolateAllocate( pd, 1, 1 );

 

      // Use tolerance as a function of size of source data

      double tol2 = image->GetLength();

      tol2 = tol2 ? tol2*tol2 / 1000.0 : 0.001;

 

      // Find the cell that contains pos

      int subId;

      double pcoords[3], weights[8];

      vtkCell* cell = image->FindAndGetCell(

          pos, NULL, -1, tol2, subId, pcoords, weights );

      if( cell )

        {

        // Interpolate the point data

        this->PointData->InterpolatePoint( pd, 0, cell->PointIds, weights );

        int components =

          this->PointData->GetScalars()->GetNumberOfComponents();

        double* tuple = this->PointData->GetScalars()->GetTuple( 0 );

 

        std::string message = "Location: ( ";

        message += vtkVariant( pos[0] ).ToString();

        message += ", ";

        message += vtkVariant( pos[1] ).ToString();

        message += ", ";

        message += vtkVariant( pos[2] ).ToString();

        message += " )\nValue: ( ";

 

        for( int c = 0; c < components; ++c )

          {

          message += vtkVariant( tuple[ c ] ).ToString();

          if( c != components - 1 ) 

            {

            message += ", ";

            }

          }

        message += " )";

        this->Annotation->SetText( 0, message.c_str() );

        interactor->Render();

        style->OnMouseMove();

        }

    }

 

private:

 

  // Pointer to the viewer

  vtkImageViewer2 *Viewer;

 

  // Pointer to the picker

  vtkPropPicker *Picker;

 

  // Pointer to the annotation

  vtkCornerAnnotation *Annotation;

 

  // Interpolator

  vtkPointData* PointData;

};

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