[vtkusers] Help with Vtk when rendering millions of points

[David Doria]

On Tue, Aug 7, 2012 at 5:19 AM, ikatz <ikatzbilb at hotmail.com> wrote:

> I can't provide a self-contained example because the code is quite complex
> and uses another libraries for other purposes, it would be impossible to
> compile everything. Anyway, I will try to explain as best as possible.
> We are using what we call gfxPointClouds, an structure that holds all the
> poins of the point cloud, and after getting the number of points we use
> vtkPolyData structures to manage all the points. This point cloud element
> is
> treated as other elements like spheres or lines in our vtkRenderWindow, the
> problem is that when we want to "refresh" the whole Viewport (working with
> >10 million point clouds) it takes a lot of time (sometimes 1 minute) or
> does not even load the point cloud and the program fails. I don't know if
> there is another way of managing this point clouds structures in VTK other
> than vtkPolyData or if it's normal to last so match...
>
> Here is the code:
>
> const gfxPointCloud3* cop = dynamic_cast<const
> gfxPointCloud3*>(pointCloud);
>         unsigned int iNumPoints = cop->GetNumElements();
>
>         //Reset to an empty state and free any memory.
>         m_PolyData->Initialize();
>
>         //No points, no work.
>         if( iNumPoints > 0 )
>         {
>                 vtkPoints* pointSet = vtkPoints::New();
>                 pointSet->Allocate(iNumPoints);
>                 vtkCellArray* cellSet = vtkCellArray::New();
>                 vtkBitArray* selectSet = vtkBitArray::New();
>                 vtkFloatArray* scalarSet = vtkFloatArray::New();
>
>                 pointSet->SetNumberOfPoints( iNumPoints );
>                 selectSet->SetNumberOfValues( iNumPoints );
>
>                 switch( cop->GetAttributeSize() )
>                 {
>                         case 1: //char (8 bits)
>                         case 2: //short (16 bits)
>                         case 4: //int (32 bits)
>                         case 8: //double (64 bits)
>                                 m_AttributeSize = cop->GetAttributeSize();
>                                 scalarSet->SetNumberOfValues( iNumPoints );
>                                 bAttribute = true;
>                                 break;
>                         default: //invalid size: disable the color map.
>                                 m_AttributeSize = 0;
>                                 m_Map->ScalarVisibilityOff();
>                 }
>
>                 gfxPoint3 point;
>                 for( unsigned int i=0; i<iNumPoints; i++ )
>                 {
>                         //Add the point to the point list.
>                         point = cop->GetElement(i);
>                         pointSet->SetPoint(     i, point.x(), point.y(),
> point.z() );
>
>                         //Create a new cell and add the new point to it.
>                         cellSet->InsertNextCell( 1 );
>                         cellSet->InsertCellPoint( i );
>
>                         //Mark the new point as not selected.
>                         selectSet->SetValue( i, 0 );
>
>                         //IF{} just to speed-up when there is no attribute
> in the point cloud.
>                         if( bAttribute )
>                         {
>                                 switch( m_AttributeSize )
>                                 {
>                                         //All types are converted to float.
>                                         case 1: //char (8 bits)
>                                                 scalarSet->SetValue( i,
> *((char*)(cop->GetAttribute(i))) );
>                                                 break;
>                                         case 2: //short (16 bits)
>                                                 scalarSet->SetValue( i,
> *((short*)(cop->GetAttribute(i))) );
>                                                 break;
>                                         case 4: //int (32 bits)
>                                                 scalarSet->SetValue( i,
> *((int*)(cop->GetAttribute(i))) );
>                                                 break;
>                                         case 8: //double (64 bits)
>                                                 scalarSet->SetValue( i,
> *((double*)(cop->GetAttribute(i))) );
>                                                 break;
>                                 }
>                         }
>                 }
>
>                 m_PolyData->SetPoints( pointSet );
>                 m_PolyData->SetVerts( cellSet );
>
>                 //Associate the selection scalar with the cells.
>                 m_PolyData->GetCellData()->SetScalars( selectSet );
>
>                 //Associate the attribute scalar with the points.
>                 if( bAttribute )
>                         m_PolyData->GetPointData()->SetScalars( scalarSet
> );
>
>                 m_PolyData->Modified();
>
>                 m_Map->SetInput( m_PolyData );
>                 m_SelectionMap->SetInput( m_PolyData );
>
>                 scalarSet->Delete();
>                 selectSet->Delete();
>                 cellSet->Delete();
>                 pointSet->Delete();
>          }
>

You should be able to turn that into a working demo without much trouble.
It looks like you can just replace your custom data type with a
 vtkPointSource (
http://www.vtk.org/Wiki/VTK/Examples/Cxx/PolyData/PointSource ) to produce
some random data. Of course you'll also have to make the member variables
defined in this demo scope, etc.

David
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