[vtkusers] help

[hbfyf]

I'm a university student from China and I have learned VTK for some time.I studied an example of VTK which demonstrates cell picking using vtkCellPicker.My questions are followed:
 1.where is (0,0,0) or where is the origin?
 2.Can you help me do some improvement?This example uses a picture drawed by the code itself.How to improve the code to load a file of .ply and then get coordinate value?
 3.This program only demonstrates the coordinate value when I click at somewhere.How to improve the code to get normal vector of every triangle which is made up by three points?
  
 I'm looking forward to your reply!Thanks!
  
 Here is the code:
 #include "vtkSphereSource.h"
#include "vtkPolyDataMapper.h"
#include "vtkLODActor.h"
#include "vtkConeSource.h"
#include "vtkGlyph3D.h"
#include "vtkCellPicker.h"
#include "vtkTextMapper.h"
#include "vtkActor2D.h"
#include "vtkInteractorStyleTrackballCamera.h"
#include "vtkRenderer.h"
#include "vtkRenderWindow.h"
#include "vtkRenderWindowInteractor.h"
#include "vtkTextProperty.h"
#include "vtkCallbackCommand.h"
#include "vtkCamera.h"
 int MouseMotion;
vtkRenderer *ren1;
vtkRenderWindow *renWin;
vtkRenderWindowInteractor *iren;
vtkCellPicker *picker;
vtkActor2D *textActor;
vtkTextMapper *textMapper;
 class PickCommand : public vtkCommand
{
public:
    static PickCommand *New() { return new PickCommand; }
   void Delete() { delete this; }
    virtual void Execute(vtkObject *caller, unsigned long l, void *callData)
   {
        if (picker->GetCellId() < 0 )
       {
           textActor->VisibilityOff();
       }
       else
       {
            double selpt[3];
           picker->GetSelectionPoint(selpt);
           double x = selpt[0];
           double y = selpt[1];
           double pickPos[3];
           picker->GetPickPosition( pickPos );
           double xp = pickPos[0];
           double yp = pickPos[1];
           double zp = pickPos[2];
            char text[120];
           sprintf( text, "(%5.5f,  %5.5f,  %5.5f)", xp, yp, zp );
           textMapper->SetInput( text );
            textActor->SetPosition(x, y);
           textActor->VisibilityOn();
       }
        renWin->Render();
   }
};
 
void PickerInteractionCallback( vtkObject* vtkNotUsed(object),
                                      unsigned long event,
                                      void* clientdata,
                                      void* vtkNotUsed(calldata) )
{
   vtkInteractorStyleTrackballCamera * style =
(vtkInteractorStyleTrackballCamera*)clientdata;
   switch( event )
   {
   case vtkCommand::LeftButtonPressEvent:
       MouseMotion = 0;
       style->OnLeftButtonDown();
       break;
   case vtkCommand::LeftButtonReleaseEvent:
       if (MouseMotion == 0)
       {
           int *pick = iren->GetEventPosition();
           picker->Pick((double)pick[0], (double)pick[1], 0.0, ren1);
       }
       style->OnLeftButtonUp();
       break;
   case vtkCommand::MouseMoveEvent:
       MouseMotion = 1;
       style->OnMouseMove();
       break;
   }
}
 
int main(int argc, char* argv)
{
   MouseMotion = 0;
   vtkSphereSource *sphere = vtkSphereSource::New();
    vtkPolyDataMapper *sphereMapper = vtkPolyDataMapper::New();
    sphereMapper->SetInput(sphere->GetOutput());
   sphereMapper->GlobalImmediateModeRenderingOn();
    vtkLODActor *sphereActor = vtkLODActor::New();
   sphereActor->SetMapper(sphereMapper);
 // create the spikes by glyphing the sphere with a cone.  Create the mapper
// and actor for the glyphs.
   vtkConeSource *cone = vtkConeSource::New();
   vtkGlyph3D *glyph = vtkGlyph3D::New();
    glyph->SetInput(sphere->GetOutput());
   glyph->SetSource(cone->GetOutput());
   glyph->SetVectorModeToUseNormal();
   glyph->SetScaleModeToScaleByVector();
   glyph->SetScaleFactor(0.25);
    vtkPolyDataMapper *spikeMapper = vtkPolyDataMapper::New();
   spikeMapper->SetInput(glyph->GetOutput());
   vtkLODActor *spikeActor = vtkLODActor::New();
   spikeActor->SetMapper(spikeMapper);
 // Create a cell picker.
   PickCommand* pickObserver = PickCommand::New();
   picker = vtkCellPicker::New();
   picker->AddObserver( vtkCommand::EndPickEvent, pickObserver );
 // Create a text mapper and actor to display the results of picking.
   textMapper = vtkTextMapper::New();
   vtkTextProperty *tprop = textMapper->GetTextProperty();
   tprop->SetFontFamilyToArial();
   tprop->SetFontSize(12);
   tprop->BoldOn();
//    tprop->ShadowOn();
   tprop->SetColor(1, 0, 0);
   textActor = vtkActor2D::New();
   textActor->VisibilityOff();
   textActor->SetMapper(textMapper);
 
// Create the Renderer, RenderWindow, and RenderWindowInteractor
 
   vtkInteractorStyleTrackballCamera *style =
vtkInteractorStyleTrackballCamera::New();
   vtkCallbackCommand * pickerCommand = vtkCallbackCommand::New();
   pickerCommand->SetClientData(style);
   pickerCommand->SetCallback(PickerInteractionCallback);
   style->AddObserver(vtkCommand::LeftButtonPressEvent, pickerCommand);
   style->AddObserver(vtkCommand::MouseMoveEvent, pickerCommand);
   style->AddObserver(vtkCommand::LeftButtonReleaseEvent, pickerCommand);
    ren1 = vtkRenderer::New();
   renWin = vtkRenderWindow::New();
   renWin->AddRenderer(ren1);
   iren = vtkRenderWindowInteractor::New();
   iren->SetRenderWindow(renWin);
   iren->SetInteractorStyle(style);
   iren->SetPicker(picker);
 
// Add the actors to the renderer, set the background and size
 
   ren1->AddActor2D(textActor);
   ren1->AddActor(sphereActor);
   ren1->AddActor(spikeActor);
   ren1->SetBackground(1, 1, 1);
    renWin->SetSize(300, 300);
 // Get the camera and zoom in closer to the image.
   vtkCamera *cam1 = ren1->GetActiveCamera();
   cam1->Zoom(1.4);
    iren->Initialize();
   iren->Start();
    picker->RemoveObserver( pickObserver );
   sphere->Delete();
   sphereMapper->Delete();
   sphereActor->Delete();
   cone->Delete();
   glyph->Delete();
   spikeMapper->Delete();
   spikeActor->Delete();
   picker->Delete();
   textMapper->Delete();
   textActor->Delete();
   pickerCommand->Delete();
   style->Delete();
   ren1->Delete();
   renWin->Delete();
   pickObserver->Delete();
//    iren->Delete();
 
   return 0;
}
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