[vtkusers] Deleting points form vtkPolyData object

[Bill Lorensen]

BTW: I think you will be disappointed. DeletePoint does not really
delete a point in the polydata.

I'll leave as a exercise to the reader to see what it does.

Hint: in all of VTK it is only used in vtkDecimatePro and vtkQuadricDecimation.

Bill

On Mon, Nov 2, 2009 at 12:39 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> Looking at the code in vtkPolydata.h, DeletePoint must be preceeded by
> BuildLinks(). I'm not sure why, but here is the current
> implementation:
> inline void vtkPolyData::DeletePoint(vtkIdType ptId)
> {
>  this->Links->DeletePoint(ptId);
> }
>
> Since Links is NULL until BuildLinks() is called, this will seg fault
> as you both discovered.
>
> Bill
>
>
> On Mon, Nov 2, 2009 at 12:26 PM, David Doria <daviddoria+vtk at gmail.com> wrote:
>> On Mon, Nov 2, 2009 at 12:24 PM, da <remywendy at gmail.com> wrote:
>>> Its not clear if you're adding multiple points or not...
>>>
>>> Given the code you've included, you're only inserting one point from the
>>> line
>>> m_Points->GetPoints()->InsertNextPoint(m_daPointPosition);
>>> and then deleting the second point (index 1, but you only have index 0),
>>> which would cause a null pointer exception?
>>>
>>>
>>> If you're adding multiple points in the lines of code that are not included,
>>> make sure to include them.
>>>
>>>
>>>
>>> On Mon, Nov 2, 2009 at 1:30 AM, Lodron, Gerald <Gerald.Lodron at joanneum.at>
>>> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I stored a point list into the vtkPolyData object using these lines:
>>>>
>>>> //m_Points ... vtkPolyData Object pointer
>>>> //m_daPointPosition ... Three dimensional double array specifying x,y and
>>>> z coordinate of the point
>>>>
>>>> m_Points->GetPoints()->InsertNextPoint(m_daPointPosition);
>>>> m_Points->GetVerts()->InsertNextCell(1);
>>>>
>>>> m_Points->GetVerts()->InsertCellPoint(m_Points->GetPoints()->GetNumberOfPoints()-1);
>>>> m_Points->Update();
>>>>
>>>> This works fine, I also can visualize it. Now I want to delete a specific
>>>> point, e.g. the second point which was inserted, but I always get a null
>>>> pointer exception:
>>>>
>>>> m_Points->DeletePoint(1); //Null pointer exception
>>>> m_Points->DeleteCell(1);
>>>>
>>>> vtkCleanPolyData *Cleaner = vtkCleanPolyData::New();
>>>> Cleaner->SetInput(m_Points);
>>>> Cleaner->Update();
>>>>
>>>> m_Points = Cleaner->GetOutput();
>>>> m_Points->Update();
>>>> m_Points->BuildCells();
>>>> m_Points->BuildLinks();
>>>>
>>>> Cleaner = NULL; //Use smart pointers to delete
>>>>
>>>>
>>>> Have anybody a suggestion what i made false?
>>>> _______________________________________________
>>>> Powered by www.kitware.com
>>>>
>>>> Visit other Kitware open-source projects at
>>>> http://www.kitware.com/opensource/opensource.html
>>>>
>>>> Please keep messages on-topic and check the VTK FAQ at:
>>>> http://www.vtk.org/Wiki/VTK_FAQ
>>>>
>>>> Follow this link to subscribe/unsubscribe:
>>>> http://www.vtk.org/mailman/listinfo/vtkusers
>>>
>>>
>>> _______________________________________________
>>> Powered by www.kitware.com
>>>
>>> Visit other Kitware open-source projects at
>>> http://www.kitware.com/opensource/opensource.html
>>>
>>> Please keep messages on-topic and check the VTK FAQ at:
>>> http://www.vtk.org/Wiki/VTK_FAQ
>>>
>>> Follow this link to subscribe/unsubscribe:
>>> http://www.vtk.org/mailman/listinfo/vtkusers
>>>
>>>
>>
>> I also get a segfault. Here is my example:
>>
>> #include <vtkSmartPointer.h>
>> #include <vtkPoints.h>
>> #include <vtkPolyData.h>
>>
>> int main(int argc, char *argv[])
>> {
>>  //create a set of points
>>  vtkSmartPointer<vtkPoints> Points = vtkSmartPointer<vtkPoints>::New();
>>  Points->InsertNextPoint ( 1.0, 0.0, 0.0 );
>>  Points->InsertNextPoint ( 0.0, 0.0, 0.0 );
>>  Points->InsertNextPoint ( 0.0, 1.0, 0.0 );
>>
>>  vtkSmartPointer<vtkPolyData> Polydata = vtkSmartPointer<vtkPolyData>::New();
>>  Polydata->SetPoints(Points);
>>
>>  vtkstd::cout << "Number of points: " <<
>> Polydata->GetNumberOfPoints() << vtkstd::endl;
>>
>>  Polydata->DeletePoint(1);//segfault on this line
>>
>>  vtkstd::cout << "Number of points: " <<
>> Polydata->GetNumberOfPoints() << vtkstd::endl;
>>
>>  return 0;
>> }
>>
>>
>> Thanks,
>>
>> David
>> _______________________________________________
>> Powered by www.kitware.com
>>
>> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>>
>> Please keep messages on-topic and check the VTK FAQ at: http://www.vtk.org/Wiki/VTK_FAQ
>>
>> Follow this link to subscribe/unsubscribe:
>> http://www.vtk.org/mailman/listinfo/vtkusers
>>
>