[vtkusers] Re: Pb using vtkAppendPolyData & vtkPolyDataConnectivityFilter - Error in a vtk class?

[TDeschamps at lbl.gov]

Dear vtkUsers,

Trying to find a solution to my problem, I went on studying the
vtkPolyDataConnectivityFilter.cxx file, and I've found something which
explains why it takes so long, but I am not sure if it is done on
purpose or if it is a mistake:

If I try to use this filter to get all connected regions:

vtkPolyDataConnectivityFilter * connectivity =
vtkPolyDataConnectivityFilter::New ();
 connectivity -> SetInput( myPolyData );
 connectivity -> SetExtractionModeToSpecifiedRegions();
 connectivity -> Update();

Then the following code returns

myPolyData -> GetNumberOfLines(); -->  29552
myPolyData -> GetNumberOfPoints(); --> 29572

connectivity -> GetNumberOfExtractedRegions(); --> 228
connectivity -> AddSpecifiedRegion(10);
connectivity -> Update();
connectivity -> GetOutput() -> GetNumberOfLines(); --> 194
connectivity -> GetOutput() -> GetNumberOfPoints(); --> 29572!!!

The number of points in one of the regions is exactly the same than the
total number of points. If I append all the regions with
vtkAppendPolyData the total number of points will therefore be 228 x
29572 > 6.10^6, while it should be 29572 only.

Notice that the number of lines is correct.

So my question is: is there something I did not catch in the way this
filter works, or is it an error?

Thomas (tdeschamps at lbl.gov)

----- Original Message -----
From: Thomas Deschamps <tdeschamps at lbl.gov>
Date: Wednesday, April 16, 2003 3:36 pm
Subject: Re: Pb using vtkAppendPolyData & vtkPolyDataConnectivityFilter

> Dear vtkUsers,
> 
> I am still trying to select some 2D contours which are smaller or 
> equal 
> to a given number of lines (not all contours are closed)
> 
> I've found something that I don't understand using 
> vtkPolyDataConnectivityFilter & vtkAppendPolyData.
> Using the code mentionned in the previous thread, i've realized 
> that the 
> myPolyData is strangely modified by this routine. If I keep a copy 
> of my 
> object and I compare them after, I can see that:
> 
> Before:
>  Verts = 0x87bd290
>  Lines = 0x862cbb0
>  Polys = 0x862cc58
>  Strips = 0x8624f80
> 
> After
>  Verts = 0x0
>  Lines = 0x85a3ea8
>  Polys = 0x0
>  Strips = 0x0
> 
> And I've found another strange behavior: if I rerun the same 
> routine on 
> my new polydata, it takes MUCH longer (x10).
> All this time is takent by connectivity -> Update();
> It is like the polydata created by vtkAppendPolyData takes more 
> time to 
> be accessed by  the method SetExtractionModeToSpecifiedRegions();
> Anyone has an idea?
> 
> Thomas
> 
> Thomas Deschamps wrote:
> 
> > Hi vtkUsers,
> >
> > I am using vtkAppendPolyData for selecting contours which have a 
> > certain length among all the contours I have.
> > My problem is that it takes a LOT of time.
> >
> > The following code remove all the closed contours which have a 
> length 
> > smaller than contourLength
> >           void function( int contourLength, vtkPolyData * 
> myPolyData )
> > {
> >    vtkPolyDataConnectivityFilter * connectivity = 
> > vtkPolyDataConnectivityFilter::New ();
> >    connectivity -> SetInput( myPolyData );
> >    connectivity -> SetExtractionModeToSpecifiedRegions();
> >    connectivity -> Update();
> >
> >    vtkPolyData * localPolyData = vtkPolyData::New();
> >    int nbRegions = connectivity -> GetNumberOfExtractedRegions();
> >              for( int i = 0 ; i < nbRegions ; i++ ) {
> >        vtkAppendPolyData * append = vtkAppendPolyData::New();
> >        connectivity -> AddSpecifiedRegion(i);
> >        connectivity -> Update();
> >        int nbLines = connectivity -> GetOutput() -> 
> GetNumberOfLines();>                                     if( 
> nbLines >= contourLength )
> >            append -> AddInput( connectivity -> GetOutput() );
> >                      append -> AddInput( localPolyData );
> >        append -> Update();
> >        localPolyData -> DeepCopy( append -> GetOutput());
> >        connectivity -> DeleteSpecifiedRegion(i);
> >        append -> Delete();
> >     }
> >                          myPolyData -> DeepCopy( localPolyData );
> >     localPolyData -> Delete();
> >     connectivity -> Delete();
> > }
> >
> > You may ask why I am not using the "append" outside of the loop.
> > This is because it looks like append -> AddInput() is not making 
> a 
> > copy of the input polydata, but keeps track of the pointer, even 
> if 
> > this pointer is modified in the future. Therefore it was not 
> working 
> > like that.
> >
> > When the number of contours is > 1000, and when each contour is 
> > between 4 and 700 lines, it takes 30 minutes...
> > There is surely something more efficient that what I am doing, 
> but I 
> > don't know what.
> > Thank you for reading this.
> >
> > Thomas (tdeschamps at lbl.gov)
> >
> >
> >
> 
> 
>