vtkImageImport -> cell data

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vtkImageImport -> cell data

Martin Genet-3
Hey everyone,

I'm realizing that vtkImageImport generates images with point data, not
cell data—the Detailed Description says "The array applies on scalar
point data only, not on cell data." I was wondering why? I would expect
it to read the data as cell data, with one value per voxel. Thanks for
helping to understand!

Martin
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Re: vtkImageImport -> cell data

Cory Quammen-2
Hi Martin,

While your expectation is understandable, in VTK voxel data is
associated with points.

Cory

On Mon, Jan 18, 2016 at 6:27 AM, Martin Genet
<[hidden email]> wrote:

> Hey everyone,
>
> I'm realizing that vtkImageImport generates images with point data, not cell
> data—the Detailed Description says "The array applies on scalar point data
> only, not on cell data." I was wondering why? I would expect it to read the
> data as cell data, with one value per voxel. Thanks for helping to
> understand!
>
> Martin
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at:
> http://www.vtk.org/Wiki/VTK_FAQ
>
> Search the list archives at: http://markmail.org/search/?q=vtkusers
>
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--
Cory Quammen
R&D Engineer
Kitware, Inc.
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Re: vtkImageImport -> cell data

David Gobbi
In reply to this post by Martin Genet-3
Hi Martin,

In VTK, image data is point data, one data value per point.  Cell data isn't used because the vtkVoxel cell is not a voxel in the conventional sense: a vtkVoxel is a finite element that connects 8 points, where each corner point generally has a data value (use of point scalars in VTK is much more common than the use of cell scalars).  So the typical usage of vtkVoxel is contrary to the conventional definition of "voxel" which has just one data value.

The VTK image processing filters work on point data, because a VTK point fits the conventional definition of "voxel" (i.e. a voxel defined as one data sample in a volumetric grid of such samples) better than vtkVoxel does.

 - David  

On Mon, Jan 18, 2016 at 4:27 AM, Martin Genet <[hidden email]> wrote:
Hey everyone,

I'm realizing that vtkImageImport generates images with point data, not cell data—the Detailed Description says "The array applies on scalar point data only, not on cell data." I was wondering why? I would expect it to read the data as cell data, with one value per voxel. Thanks for helping to understand!

Martin

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Re: vtkImageImport -> cell data

Martin Genet-3
Thanks so much, Cory and David! Martin

On 18/01/2016 14:45, David Gobbi wrote:
Hi Martin,

In VTK, image data is point data, one data value per point.  Cell data isn't used because the vtkVoxel cell is not a voxel in the conventional sense: a vtkVoxel is a finite element that connects 8 points, where each corner point generally has a data value (use of point scalars in VTK is much more common than the use of cell scalars).  So the typical usage of vtkVoxel is contrary to the conventional definition of "voxel" which has just one data value.

The VTK image processing filters work on point data, because a VTK point fits the conventional definition of "voxel" (i.e. a voxel defined as one data sample in a volumetric grid of such samples) better than vtkVoxel does.

 - David  

On Mon, Jan 18, 2016 at 4:27 AM, Martin Genet <[hidden email]> wrote:
Hey everyone,

I'm realizing that vtkImageImport generates images with point data, not cell data—the Detailed Description says "The array applies on scalar point data only, not on cell data." I was wondering why? I would expect it to read the data as cell data, with one value per voxel. Thanks for helping to understand!

Martin


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