[vtkusers] algorithm performance

[Gerrick Bivins]

Bill,Jeff,
Currently, the slices will be orthogonal slices, parallel to the Cartesian axes (x,y,z).
Next request will be multiple arbitrarily oriented slices but probably parallel to each other (same normal).

Still absorbing this. It's not quite clear how I'd generate a planar slice using vtkCutter from the scalar data.
Can either of you point me to some example code?
Gerrick

From: Jeff Lee [mailto:jlee1549 at gmail.com]
Sent: Friday, August 02, 2013 12:01 PM
To: Bill Lorensen
Cc: Gerrick Bivins; vtkusers at vtk.org
Subject: Re: [vtkusers] algorithm performance

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<mailto: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<mailto: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<mailto:bill.lorensen at gmail.com>]
Sent: Friday, August 02, 2013 10:18 AM
To: Gerrick Bivins
Cc: vtkusers at vtk.org<mailto: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<mailto: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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