[vtkusers] Unstructured grid renderer artefacts ?

[Moreland, Kenneth]

I'm re-sending this messages with the attachments stripped off.

-Ken

> -----Original Message-----
> From: Moreland, Kenneth 
> Sent: Friday, September 23, 2005 8:25 AM
> To: 'Zsolt '; vtkusers at vtk.org
> Subject: RE: [vtkusers] Unstructured grid renderer artefacts ?
> 
> Zsolt,
> 
> Your problems stem from the fact that unstructured grid 
> volume rendering was still in its infancy for the release of 
> VTK 4.4.  Your problems can probably be solved by upgrading 
> to VTK 5.0 (which should have a beta release very soon).  The 
> small pink dots you see are an artifact from approximations 
> made during ray integration.  These approximations lead to 
> artifacts when you have sharp changes in color and opacity, 
> as you have in your data.  The ray integration is much 
> improved in VTK 5.0 and these artifacts should go away.  See 
> the attached ball.png.
> 
> The white dots and lines you see in the axis aligned view are 
> caused by a bug in vtkUnstructuredGridVolumeRayCastMapper 
> (well, technically in its helper class 
> vtkUnstructuredGridBunykRayCastFunction).  It is a numerical 
> instability that occurs when a ray hits exactly at an edge or 
> point of a cell and then traverses into the incorrect 
> neighbor.  This bug still exists in VTK 5.0, but you also 
> have a choice of mappers now.  
> vtkUnstructuredGridZSweepMapper is slightly slower, but uses 
> far less memory and does not have the numerical instabilities 
> that the ray cast mapper can have.  There is also 
> vtkProjectedTetrahedraMapper.  It is much faster than the 
> other two methods (especially if you have a graphics card), 
> but it takes many liberties in its color computations, so 
> your "little pink dot" artifacts actually become much worse 
> (see the attached ball_pt.png).
> 
> -Ken
> 
> > -----Original Message-----
> > From: vtkusers-bounces+kmorel=sandia.gov at vtk.org
> > [mailto:vtkusers-bounces+kmorel=sandia.gov at vtk.org] On 
> Behalf Of Zsolt
> > Sent: Friday, September 23, 2005 5:53 AM
> > To: vtkusers at vtk.org
> > Subject: [vtkusers] Unstructured grid renderer artefacts ?
> > 
> > Dear VTK users,
> > 
> > I`m using VTK 4.4 under Visual C++ 7.1 for unstructured 
> grid rendering 
> > and I`m getting strange artefacts, like small dots in the results:
> >    see link      http://www.sccg.sk/~toth/vtk/06.tiff
> > or if it is viewed axis alligned:
> >     see link     http://www.sccg.sk/~toth/vtk/18.tiff
> > 
> > the dataset can be found at:   link: 
> > http://www.sccg.sk/~toth/vtk/input.vtk
> > 
> > The code of the application:
> > 
> > #include "vtkConeSource.h"
> > #include "vtkPolyDataMapper.h"
> > #include "vtkRenderWindow.h"
> > #include "vtkRenderWindowInteractor.h"
> > #include "vtkCamera.h"
> > #include "vtkActor.h"
> > #include "vtkRenderer.h"
> > #include "vtkRendererSource.h"
> > #include "vtkTIFFWriter.h"
> > 
> > #include "vtkVolumeRayCastMapper.h"
> > #include "vtkVolumeRayCastCompositeFunction.h"
> > #include "vtkUnstructuredGridVolumeRayCastMapper.h"
> > #include "vtkStructuredPoints.h"
> > #include "vtkUnstructuredGridReader.h"
> > #include "vtkDataReader.h"
> > #include <stdio.h>
> > 
> > #include "vtkPiecewiseFunction.h"
> > #include "vtkColorTransferFunction.h"
> > #include "vtkVolumeProperty.h"
> > 
> > #include "vtkDataArray.h"
> > #include "vtkErrorCode.h"
> > #include "vtkFieldData.h"
> > #include "vtkObjectFactory.h"
> > #include "vtkPointData.h"
> > #include "vtkStructuredPoints.h"
> > #include <vtkUnsignedShortArray.h>
> > #include "vtkCellData.h"
> > 
> > #include <iostream>
> > using namespace std;
> > 
> > 
> > #include "vtkDataReader.h"
> > 
> > 
> > int main( int argc, char *argv[] )
> > {
> >   // volume property
> >   int shade = 0, 
> > 	  compos = 0,  //Classify First or Interpolate First 
> > 	  interp = 0;
> > 
> >   // renderer
> >   vtkRenderer *ren1= vtkRenderer::New();
> >   ren1->SetBackground( 1.0, 1.0, 1.0 );
> >   
> >   // render window
> >   vtkRenderWindow *renWin = vtkRenderWindow::New();
> >   renWin->AddRenderer( ren1 );
> >   renWin->SetSize( 800, 600 );
> > 
> >   // interactor
> >   vtkRenderWindowInteractor *iren1 = 
> vtkRenderWindowInteractor::New();
> >   iren1->SetRenderWindow(renWin);
> > 
> >   // set up the input file for unstructured grid reader
> >   vtkUnstructuredGridReader *unstructuredReader 
> > =vtkUnstructuredGridReader::New();
> >   unstructuredReader->SetFileName("input.vtk");
> > 
> >   // set up opacity transfer function
> >   vtkPiecewiseFunction *opacityTransferFunction = 
> > vtkPiecewiseFunction::New();
> >   opacityTransferFunction->AddPoint(0,   0.02);
> >   opacityTransferFunction->AddPoint(4095.0, 1.0);
> > 
> >   // set up color transfer function
> >   vtkColorTransferFunction *colorTransferFunction = 
> > 	  vtkColorTransferFunction::New();
> >   colorTransferFunction->AddRGBPoint( 0.0, 0.1, 0.1, 0.1);
> >   colorTransferFunction->AddRGBPoint( 4095.0, 1.0, 0.0, 1.0);	
> > 
> >   // set up volume property
> >   vtkVolumeProperty *volumeProperty = vtkVolumeProperty::New();
> >   volumeProperty->SetColor(colorTransferFunction);
> >   volumeProperty->SetScalarOpacity(opacityTransferFunction);
> >   volumeProperty->SetInterpolationType(interp);
> >   volumeProperty->SetShade(shade);
> > 
> >   // composite function for strucured grid renderer
> >   vtkVolumeRayCastCompositeFunction *compositeFunction = 
> > 	  vtkVolumeRayCastCompositeFunction::New();
> >   compositeFunction->SetCompositeMethod(compos);
> > 
> >   //unstructuredGridRendering
> >   vtkUnstructuredGridVolumeRayCastMapper
> > *volumeUnstructedMapper =
> > vtkUnstructuredGridVolumeRayCastMapper::New();
> >   volumeUnstructedMapper->SetInput(unstructuredReader->GetOutput());
> > 
> >   vtkVolume *volume = vtkVolume::New();
> > 
> >   volume->SetMapper(volumeUnstructedMapper);
> >   
> >   volume->SetProperty(volumeProperty);
> > 
> >   // add volume to renderer
> >   ren1->AddVolume(volume);
> > 
> >   renWin->Render();
> > 
> >   iren1->Start();
> >   
> >   ren1->Delete();
> >   renWin->Delete();
> >   iren1->Delete();
> >   opacityTransferFunction->Delete();
> >   colorTransferFunction->Delete();
> >   volumeProperty->Delete();
> >   compositeFunction->Delete();
> >    // unstructured grid case
> >   volumeUnstructedMapper->Delete();
> >   unstructuredReader->Delete();
> >   volume->Delete();
> > 
> >   return 0;
> > }
> > 
> > Do You have any idea what can cause these problems?
> > 
> > Many thanks, best regards
> >                                            Zsolt
> > 
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