[vtkusers] vtkPointPicker / vtkGlyph3D problem

[Gomez, Alberto]

Hi all,

I am trying to select a vector from a vector field with the mouse. The 
vector field is a glyph of vectors and it is generated in the following 
way (1). Then I use a custom interaction (subclassing 
vtkInteractionStyleTrackballCamera) so that I pick points when I press 
the mouse button (2). When I click the left button, a callback (3) does 
some processing. The problem is that the position I get does not match 
the real vector position (i.e. I plot a vector at the 3D point I get 
with the picker through the method picker->GetPickPosition() and it does 
not match). Anyone has a clue on why? I have played around with the 
tolerance with no success.

Another question, how can I get the point information (vector and 
position) from the point id??

Thanks,

Alberto


(1) Vector field generation :

//positions
    vtkSmartPointer<vtkPoints> pts = vtkSmartPointer<vtkPoints>::New();
    pts->SetNumberOfPoints(num_pts);
//directions
    vtkSmartPointer<vtkDoubleArray> vecArr =   
vtkSmartPointer<vtkDoubleArray>::New();
    vecArr->SetNumberOfComponents(3);
    vecArr->SetNumberOfTuples(num_pts);
    for (int i = 0; i < num_pts; i++) {
            pts->InsertNextPoint(positions[i][0], positions[i][1], 
positions[i][2]);
            float tuple[3] = {(float) directions[i][0] , (float) 
directions[i][1], (float) directions[i][2]};
            vecArr->InsertNextTuple(tuple);
      }

// put vectors and positions into a grid which will be the glyph's input
    vtkSmartPointer<vtkUnstructuredGrid> uGrid = vtkSmartPointer< 
vtkUnstructuredGrid>::New();
    uGrid->SetPoints(pts);
    uGrid->GetPointData()->SetVectors(vecArr);

 // glyph construction
    vtkSmartPointer<vtkArrowSource> arrow =   
vtkSmartPointer<vtkArrowSource>::New();
    vtkSmartPointer<vtkGlyph3D> glyph = vtkSmartPointer<vtkGlyph3D>::New();
    glyph->SetInput(uGrid);
    glyph->SetSource(arrow->GetOutput());
    glyph->SetScaleModeToScaleByVector();
    glyph->GeneratePointIdsOn();
//Mapper and actor
    vtkSmartPointer<vtkPolyDataMapper> gMapper = 
vtkSmartPointer<vtkPolyDataMapper>::New();
    gMapper->SetInput(glyph->GetOutput());
    gMapper->ScalarVisibilityOff();
    gMapper->SetScalarRange(uGrid->GetScalarRange());

vtkSmartPointer<vtkActor> gactor = vtkSmartPointer<vtkActor>::New();
    gactor->SetMapper(gMapper);
    gactor->GetProperty()->SetColor(color);
    ren->AddActor(gactor);

(2) Detail of my subclass for custom interactor style:
virtual void OnLeftButtonDown()
    {
         if (this->Interactor->GetControlKey() ){
                 int* pos = this->GetInteractor()->GetEventPosition();
                pointPicker->Pick(pos[0], pos[1], 0, 
this->GetDefaultRenderer());
        } else{

            vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
        }
    }

(3)  Callback class (detail)

// Callback thats get called for a picking event.
class PickCallback : public vtkCommand
{
  public:
    static PickCallback* New()
    {
     return new PickCallback();
    }

    void Execute(vtkObject* caller, unsigned long eventId, void* callData)
    {
      vtkPointPicker *picker = static_cast< vtkPointPicker* >(caller);
      if(picker->GetPointId() < 1)
      {
      // Nothing is picked.
      }
      else
      {
        double* pos = picker->GetPickPosition();
     std::cout << pos[0]<< ","<< pos[1]<< ","<< pos[2]<< std::endl;

        actor = generateVectorActor(picker);


        ren->AddViewProp(actor);


      }



    }

Allan James wrote:
> Hi all,
>
> I have an issue with code that is using vtkPointPicker to pick points displayed using vtkGlyph3D.
>
> Now I have the picking working great for most of the glyphs - using vtkGlyph3D->GeneratePointIdsOn(); and I am able to select glyphs and display a sphere at the selected glyph location.
>
> My problem is that while this works perfectly 99% of the time - there are certain glyphs that are either very difficult to pick (sometimes impossible it seems) or I have to click about 20 pixels or so above or next to the glyph for the pick to work. Has anyone seen this issue and/or can suggest a fix?
>
> Why would picking work perfectly for most glyphs but not for some others - when all of the glyphs are generated from the same simple pointset using the same vtkGlyph3D filter?
>
> Any help would be muchly appreciated - thanks
>
> Allan James
> High Performance Computing & Research Support
> Queensland University of Technology
> (07) 3138 9264
> ar.james at qut.edu.au<mailto:ar.james at qut.edu.au>
> http://www.qut.edu.au/its/hpc
>
>   
>> <(((º>  ._.·´¯`·..  >++(((º>  ._.·´¯`·..  >++(((º>
>>     
>
>
>   


-- 

Alberto Gómez

/Division of Imaging Sciences
The Rayne Institute
4th Floor, Lambeth Wing
St Thomas' Hospital
London SE1 7EH /

phone: +44 (0) 20 718 88364
email: alberto.gomez at kcl.ac.uk <mailto:alberto.gomez at kcl.ac.uk>