[vtkusers] algorithm performance

[Jeff Lee]

IIRC the unstructured grid algorithm doesn't use a cell locator to find
candidate cells, it runs over all cells and checks the scalar range of the
cell and then contours it if the range is satisfied.  Its faster than
blindly contouring every cell but not as good as it could be.  A better
approach would be to use a scalar tree (where the function value is the
scalar) and use that to locate candidate cells.  It will be expensive to
build the tree the first time, but subsequent contours of the same function
will typically be much faster, as the candidate cells have been sorted in
bins by range in the scalar tree.  You would have to modify the algorithm a
bit to do this, but i've had success with that approach in the past...


On Fri, Aug 2, 2013 at 11:46 AM, Bill Lorensen <bill.lorensen at gmail.com>wrote:

> Are the slice planes parallel to each other, or are they arbitrarily
> oriented?
>
> If they are parallel, then you could compute point data scalars once and
> leave out the implicit function. Then Cutter will use the scalar data for
> cutting. This would avoid recomputing the scalar field for each slice.
>
>
>
> On Fri, Aug 2, 2013 at 11:31 AM, Gerrick Bivins <
> Gerrick.Bivins at halliburton.com> wrote:
>
>>  Hi Bill,****
>>
>> We are building release. Our grids are large at least 10’s – 100’s of
>> thousands of cells.****
>>
>> I’m seeing the behavior in a Paraview  install as well,****
>>
>> with auto-apply on. Trying to move the slice plane through ****
>>
>> the dataset becomes less and less interactive as the dataset cell count
>> increases.****
>>
>> So I was hoping there were some ways to speed this up.****
>>
>> Any other suggestions?****
>>
>> Gerrick****
>>
>> ** **
>>
>> *From:* Bill Lorensen [mailto:bill.lorensen at gmail.com]
>> *Sent:* Friday, August 02, 2013 10:18 AM
>> *To:* Gerrick Bivins
>> *Cc:* vtkusers at vtk.org
>> *Subject:* Re: [vtkusers] algorithm performance****
>>
>> ** **
>>
>> Also be sure you build VTK and your app Release and not Debug.****
>>
>> ** **
>>
>> ** **
>>
>> On Fri, Aug 2, 2013 at 11:08 AM, Gerrick Bivins <
>> Gerrick.Bivins at halliburton.com> wrote:****
>>
>> Hi All,****
>>
>> I’m looking for suggestions on how to speed up an algorithm on large
>> unstructured grids, like vtkCutter.****
>>
>> I thought I could build an octree (or similar structure) from the input
>>  and execute the vtkCutter on the octree****
>>
>> but it’s not obvious to me how to do it. Is something like this possible?
>> ****
>>
>> How can I improve the speed of the algorithm? Performance seems to go
>> down as cell count grows.****
>>
>> Gerrick****
>>
>>  ****
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