[vtkusers] vtkCutter leaves "gaps"

[Gerrick Bivins]

Ok. I tried to  "Tetrahedralize" the dataset before using the cutter, and it produced
a "gapless" slice in paraview.
It loses the structure of the cells (everything is triangles obviously) but at least it doesn't drop elements.

What filter does "Tetrahedralize" map to in VTK?

Gerrick
From: David Gobbi [mailto:david.gobbi at gmail.com]
Sent: Friday, December 06, 2013 2:01 PM
To: Gerrick Bivins
Cc: Bill Lorensen; vtkusers at vtk.org
Subject: Re: [vtkusers] vtkCutter leaves "gaps"

Hi Gerrick,

If it's polyhedral cells, then yes, a bug is a definite possibility.  Gathering info from other poly users is the right way to go.  Sorry that I can't be of more help, but I haven't used poly cells myself.

  David

On Fri, Dec 6, 2013 at 12:47 PM, Gerrick Bivins <Gerrick.Bivins at halliburton.com<mailto:Gerrick.Bivins at halliburton.com>> wrote:
Bill,
For some reason it took a couple of tries to get that one through. Maybe attachement size was too big but it made it to the nabble list:
http://vtk.1045678.n5.nabble.com/vtkCutter-leaves-quot-gaps-quot-tt5724617.html

David,
Right, it feels like a bug in polyhedron cells.
My data was pretty simple, a block with poly cells a with varying thickness and width.
Definitely no holes. I probably can't send it along but
note there was just recently a post (probably minutes before my "BUMP" made it through) about a very similar issue:
http://vtk.1045678.n5.nabble.com/Bug-in-slice-and-clip-for-mesh-containing-VTK-POLYHEDRON-cells-tt5724879.html
It also has a problematic model attached.

Gerrick


From: David Gobbi [mailto:david.gobbi at gmail.com<mailto:david.gobbi at gmail.com>]
Sent: Friday, December 06, 2013 12:42 PM
To: Gerrick Bivins
Cc: Bill Lorensen; vtkusers at vtk.org<mailto:vtkusers at vtk.org>
Subject: Re: [vtkusers] vtkCutter leaves "gaps"

Hi Gerrick,

The cutter algorithm is fairly straightforward, it just creates a new point along each edge that is intersected by the plane.  Then it uses its knowledge about the connectivity of the original cells to join the new points together to create new cells.

The only problem I've ever seen with vtkCutter is the fact that its locator is limited by numerical precision: it might think two cells share an edge when in fact the edges are just very, very close to each other.  But the result of this is that gaps are closed, not created.

In response to the question about whether I've ever seen vtkCutter create gaps where no gaps exist in the original data, I'd have to say no.  That's not to say that it could never happen.  The vtkCutter delegates the "cutting" to the Contour methods of the various cell classes, so it is possible that your data uses a cell type with a buggy Contour implementation.  If that is the case, it would be good to know the details of your data so that someone can investigate, but my first suspicion is that the gaps are present in your original data.

  David

On Fri, Dec 6, 2013 at 11:13 AM, Bill Lorensen <bill.lorensen at gmail.com<mailto:bill.lorensen at gmail.com>> wrote:
I do not see the attachment/

On Fri, Dec 6, 2013 at 12:50 PM, Gerrick Bivins <Gerrick.Bivins at halliburton.com<mailto:Gerrick.Bivins at halliburton.com>> wrote:
I realized I sent this at a time when most people were probably offline.
Just a "BUMP" in case this got missed.
Anyone have any ideas here?
Gerrick
From: vtkusers-bounces at vtk.org<mailto:vtkusers-bounces at vtk.org> [mailto:vtkusers-bounces at vtk.org<mailto:vtkusers-bounces at vtk.org>] On Behalf Of Gerrick Bivins
Sent: Monday, November 25, 2013 8:33 AM
To: 'vtkusers at vtk.org<mailto:vtkusers at vtk.org>'
Subject: [vtkusers] vtkCutter leaves "gaps"

Hi All,
I've run into a strange problem where with some of my datasets, vtkCutter is leaving "gaps" in the output polydata.
For example, if I use a plane as the implicit function the attached image shows the result.
Anyone seen this kind of  behavior before?
Is there some setting on the vtkCutter that is perhaps causing this?

Gerrick



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