[vtkusers] vtkAppendPolydata

[David.Pont at ForestResearch.co.nz]

Shyam,
    repeatedly clipping sounds like something I have suggested, as a way of
refining a clip boundary.
This will result in polygons adjacent to the boundary being subdivided in
successively closer approximations to the clip boundary. Triangle->Clip
produces 3 new points and a net increase of 3 triangles in general (4 new-1
old). So, after 20 iterations, I am not surprised that the data set has
almost doubled in size.
Duplicate points will occur when you append the two parts back together and
as you mentioned in your subsequent response, vtkCleanPolyData reduces the
size, but only slightly.
Your problem is the highly fractured (x20) polygons around the boundary.
You could try vtkDecimate. Read up to understand the parameters so you can
control the process. You may damage the boundary and the original mesh.
Note that you could easily end up with LESS polygons than you started with,
I suggest you aim for some number slightly higher than the original.

    Dave



|--------+-------------------------------------->
|        |          "R K Shyamprakash"          |
|        |          <ramakrishna.prakash at quest-g|
|        |          lobal.com>                  |
|        |          Sent by:                    |
|        |          vtkusers-admin at vtk.org      |
|        |                                      |
|        |                                      |
|        |          07/08/2003 00:24            |
|        |                                      |
|--------+-------------------------------------->
  >------------------------------------------------------------------------------------------------------------|
  |                                                                                                            |
  |      To:     "'Jeff Lee'" <jeff at cdnorthamerica.com>                                                        |
  |      cc:     "'VTKUserList (E-mail)'" <vtkusers at www.vtk.org>                                               |
  |      Subject:     RE: [vtkusers] vtkAppendPolydata                                                         |
  >------------------------------------------------------------------------------------------------------------|




I did run it through vtkCleanPolyData. It does control the extent of
increase but it fails to resize the new data to original data size.

Thanks
Shyam

-----Original Message-----
From: vtkusers-admin at vtk.org [mailto:vtkusers-admin at vtk.org]On Behalf Of
Jeff Lee
Sent: Wednesday, August 06, 2003 5:31 PM
To: R K Shyamprakash
Cc: VTKUserList (E-mail)
Subject: Re: [vtkusers] vtkAppendPolydata


run through vtkCleanPolyData should help.
-Jeff

R K Shyamprakash wrote:

>Hello,
>          I use vtkAppendPolyData to create one actor  out of two or more
actors.
But
>I noticed that each time I get the output of vtkAppendPolyData, the number
>of points is increasing. For a test case, I clip an actor using
>vtkClipPolyData, then append the output and clipped output using
>vtkClipPolyData. I continued this for about 20 iterations. Then saved the
>polydata into a file. The size of the file has increased by 6 MB(initial
>size - 9 MB, final size - 15 MB). Is there anyway I can avoid these
>duplicate points?
>
>Thanks
>Shyam
>
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