[vtkusers] Picking Pixel

[Darshan Pai]

You can do 2 things :

1) Use a vtkCellPicker or a vtkPointPicker and they have functions
GetCellId() and GetPointId() respectively .
2) If not then use FindPoint() in the vtkPolyData ot ImageData to get your
ID .

Regards
Darshan

On Tue, Oct 19, 2010 at 10:15 AM, Xiaopeng Yang <yxp233 at postech.ac.kr>wrote:

>  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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