[vtkusers] Re: Noise after use of a clipping box

[John Biddiscombe]

Patrick,

the trouble is that the clipping code in vtk/paraview does an 
calculation of the distance of each point on the cell (8) to the box 
surface - and then insterts triangles where the sign changes - this 
means that along the edge, you get this rounding off artefact that you 
can see where the corner of the box has been missed. The correct result 
would mean creating an L shaped kind of boundary cell where the outside 
was the original data and the inside was the box edge.

One strategy to get it perfect would be to extract all the cells that 
intersect the clipping bos. Then add all the intersection points/edges, 
do a triangulation in 3D and then remove all the cells on the iside of 
the implicit function.

Messy.

JB



Patrick Brockmann wrote:

> Hi all,
>
> I try to clip an unstructured grid (layers on a sphere) with a box.
> I was expecting clean planes from the clipping planes
> defined by the different faces of the box, but I get some noise
> (small cells along the vertex of the clipping box)
>
> Is there an explanation to this ?
>
> See the image at
> http://dods.ipsl.jussieu.fr/brocksce/pv_bugs/clipbox/clipbox.png
> The vtk file used to produce this is available at:
> http://dods.ipsl.jussieu.fr/brocksce/pv_test/LMDz_temp_001.vtk
>
> Patrick
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-- 
John Biddiscombe,                            email:biddisco @ cscs.ch
http://www.cscs.ch/about/BJohn.php
CSCS, Swiss National Supercomputing Centre  | Tel:  +41 (91) 610.82.07
Via Cantonale, 6928 Manno, Switzerland      | Fax:  +41 (91) 610.82.82