[vtkusers] vtkCutter leaves "gaps"

[Jeff Lee]

the contour algorithm for polyhedra is pretty complicated and you are
probably hitting some edge case, if you can donate the test case and file a
bug then it will be easier to see where things are going wrong.
 tetrahedralization of polys might work on very simple hex geometry but it
wont work on nonconvex cells.
Jeff


On Mon, Dec 9, 2013 at 11:55 AM, David Gobbi <david.gobbi at gmail.com> wrote:

> A "Tesselator" filter, I think?
>
>
> On Mon, Dec 9, 2013 at 9:43 AM, Gerrick Bivins <
> Gerrick.Bivins at halliburton.com> wrote:
>
>>  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> 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]
>> *Sent:* Friday, December 06, 2013 12:42 PM
>> *To:* Gerrick Bivins
>> *Cc:* Bill Lorensen; 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>
>> wrote:
>>
>> I do not see the attachment/
>>
>>
>>
>> On Fri, Dec 6, 2013 at 12:50 PM, Gerrick Bivins <
>> 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] *On
>> Behalf Of *Gerrick Bivins
>> *Sent:* Monday, November 25, 2013 8:33 AM
>> *To:* '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
>>
>>
>>
>>
>>
>>
>>
>> [image: DecisionSpace® 5000.8.3 Now Available]<https://www.landmarksoftware.com/Pages/Geosciences.aspx>
>>
>>
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>>
>>
>>
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