[vtkusers] GetCenter of vtkImageData - a possible bug?

[Berk Geveci]

According to the VTK convention, you calculation is incorrect. Note that
VTK assign each value of an image to a vertex not to a cell. So if the
dimensions are {2,2,2} and spacing is {1,1,1}, the bounds of the data will
be {0, 1, 0, 1, 0, 1}. So the right way of calculating origin is:

     double origin[3], spacing[3], center[3];
     int dimensions[3];

     imageData->GetOrigin(origin);
     imageData->GetSpacing(spacing);
     imageData->GetDimensions(dimensions);

     for(int i = 0; i < 3; i++)
     {
         center[i] = origin[i] + ((dimensions[i] - 1 ) * spacing[i]))/2;
     }

Best,
-berk



On Wed, Mar 19, 2014 at 7:06 AM, chasank <chasank at gmail.com> wrote:

> Hi,
>
> I have a nifti image that has these features below:
>
>      Dimensions : {301, 370, 316}
>      Origin : {75, 107, -69.5}
>      Spacing : {0.5, 0.5, 0.5}
>
> I want to get center world point of the image. When I use GetCenter method
> of vtkImageData for this purpose, I get {150, 199.25, 9.25}. However, I
> suspected that it seems a bit wrong. And then I tried to calculate the
> center point on my own like below:
>
>      double origin[3], spacing[3], center[3];
>      int dimensions[3];
>
>      imageData->GetOrigin(origin);
>      imageData->GetSpacing(spacing);
>      imageData->GetDimensions(dimensions);
>
>      for(int i = 0; i < 3; i++)
>      {
>          center[i] = origin[i] + ((dimensions[i] / 2) * spacing[i]);
>      }
>
> and center world point becomes {150, 199.5, 9.5}. So which result is true?
> My calculation or GetCenter method?
>
> Best regards.
> Chasan
>
>
>
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