[vtkusers] Curve / Equal Subdivision

Thu Jul 12 12:55:04 EDT 2012

vtkSplineFilter uses vtkCardinalSpline as a default. Take a look at
vtkKochanekSpline as an alternative. That spline has more user controllable
parameters for controlling spline tension.

On Thu, Jul 12, 2012 at 11:32 AM, Jean-Hugues Royer <jhroyer at joher.com>wrote:

> **
> Yes this was a problem in my C# translation, I confirm that it fixes the
> issue and I get a perfect equally subdivided spline.
>
> Thanks !
>
>
> On 12/07/2012 16:53, Jerome Velut wrote:
>
> Hi,
>
> Bill, your script solved Jean-Hugues' issue with vtk-5.10 and vtk-6.0.
> Jean-Hugues, could it be a mistake in your c# translation?
>
> Jerome
>
> Le 12/07/2012 15:09, Jean-Hugues Royer a écrit :
>
> Hi,
>
> I converted it to Activiz/C#, I will let Jerome try exactly your code
> (since I can't).
>
> Regards.
>
> On 12/07/2012 14:49, Bill Lorensen wrote:
>
> In the example I sent? I happen to be running VTK6, but there should not
> have been changes.
>
> On Thu, Jul 12, 2012 at 8:35 AM, Jean-Hugues Royer <jhroyer at joher.com>wrote:
>
>>  Hi,
>>
>> If I do that, the first ~30 points have a distance of 1 and the rest
>> 0.18648.
>>
>> Regards.
>>
>>
>> On 12/07/2012 14:12, Bill Lorensen wrote:
>>
>> The splines are parameterized by an approximation to the arc length.
>> Also, the boundary conditions of the splines can affect the shape of the
>> spline. Try this version of the script:
>>
>>  #!/usr/bin/python
>> import vtk
>>
>>  lineSource = vtk.vtkLineSource( )
>> lineSource.SetPoint1( 0, 0, 0 )
>> lineSource.SetPoint2( 95, 0 ,0 )
>> lineSource.Update( )
>>
>>  mySpline = vtk.vtkCardinalSpline( )
>> mySpline.SetLeftConstraint(2)
>> mySpline.SetLeftValue(0.0)
>> mySpline.SetRightConstraint(2)
>> mySpline.SetRightValue(0.0)
>>
>>  spline = vtk.vtkSplineFilter( )
>> spline.SetSpline(mySpline)
>> spline.SetInputConnection( lineSource.GetOutputPort( ))
>> spline.SetSubdivideToLength( )
>> spline.SetLength( 0.18648 )
>> spline.Update( )
>>
>>  points = spline.GetOutput().GetPoints()
>>
>>  meanDist = 0
>>
>>  for i in range( 1, points.GetNumberOfPoints() ):
>>   pt = points.GetPoint(i)
>>   ptPrec = points.GetPoint(i-1)
>>   meanDist += pt[0] - ptPrec[0]
>>   print 'pt[',i,'] X: ',pt[0],' | Distance with previous point:',pt[0] -
>> ptPrec[0]
>>
>>  print 'Mean distance: ', meanDist / points.GetNumberOfPoints()
>> print 'Expected number of points: ', 95./0.18648
>> print 'Effective number of points: ', points.GetNumberOfPoints()
>>
>>
>>
>> On Thu, Jul 12, 2012 at 3:06 AM, Jerome Velut <jerome.velut at kitware.com>wrote:
>>
>>>  Hi Bill and Jean-Hugues,
>>>
>>> I was able to reproduce the bug for a straight line with vtk-5.10 python
>>> (script attached). I also get the same spline from paraview by exposing the
>>> vtkSplineFilter (hopefully!).
>>>
>>> Jerome
>>>
>>> Le 10/07/2012 19:09, Bill Lorensen a écrit :
>>>
>>> It is always possible that there is a bug.
>>>
>>> Can you provide a small, compilable example that illustrates the problem?
>>>
>>> On Tue, Jul 10, 2012 at 10:50 AM, Jean-Hugues Royer <jhroyer at joher.com>wrote:
>>>
>>>>  Hi,
>>>>
>>>> I also tried vtkSplineFIlter using SetSubdivideToLength() and
>>>> SetLength(distance).
>>>>
>>>> But the result is that the points are not equally distributed.
>>>>
>>>> When you provide a curve the beginning and ending points are not
>>>> equally distributed while the center points are.
>>>>
>>>> When you provide a straight line no points at all are equally
>>>> distributed.
>>>>
>>>> I get exact same result when using
>>>> vtkSplineFIlter/SetSubdivideToLength/SetLength and
>>>> vtkParametricSpline/SetParametricFunction/SetUResolution.
>>>>
>>>> May be I'm missing something ?
>>>>
>>>>
>>>> On 10/07/2012 16:21, Bill Lorensen wrote:
>>>>
>>>> Look at vtkSplineFIlter
>>>> Here is one use:
>>>> http://vtk.org/Wiki/VTK/Examples/Cxx/PolyData/FitSplineToCutterOutput
>>>>
>>>>
>>>>  On Tue, Jul 10, 2012 at 9:59 AM, Jean-Hugues Royer <jhroyer at joher.com>wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> I have a curve which is a vtkPoints array.
>>>>>
>>>>> I would like to generate another vtkPoints array where every
>>>>> consecutive points have the same distance. (basically divide the curve to n
>>>>> equals segments)
>>>>>
>>>>> I tried to use vtkParametricSpline/vtkParametricFunctionSource but I
>>>>> was only able to change the number of points to another value but I didn't
>>>>> find how to specify that these new points should be equally distributed.
>>>>>
>>>>> Any idea ?
>>>>>
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>>>>
>>>>
>>>>
>>>> --
>>>> Unpaid intern in BillsBasement at noware dot com
>>>>
>>>>
>>>
>>>
>>> --
>>> Unpaid intern in BillsBasement at noware dot com
>>>
>>>
>>>
>>> _______________________________________________
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>>>
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>>>
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>>>
>>>   --
>>> Jérôme Velut
>>> R&D Engineer
>>> Kitware SAS
>>> 26 rue Louis Guérin
>>> 69100 Villeurbanne, France
>>> F: +33 (0)4.37.45.04.15http://www.kitware.fr
>>>
>>>
>>
>>
>>  --
>> Unpaid intern in BillsBasement at noware dot com
>>
>>
>
>
>  --
> Unpaid intern in BillsBasement at noware dot com
>
>
>
> --
> Jérôme Velut
> R&D Engineer
> Kitware SAS
> 26 rue Louis Guérin
> 69100 Villeurbanne, France
> F: +33 (0)4.37.45.04.15http://www.kitware.fr
>
>

-- 
Unpaid intern in BillsBasement at noware dot com
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