[vtkusers] vtkPolyDataToImageStencil

[Nil Goyette]

Hi David,

Haha, wow, I was totally not understanding this method! It does make  
sense now. Thank you :)

One last question, just to be sure, what does the y and z parameters 
become? Here's the complete method, for clarity and for the next vtk users:
bool GetNext(int& x1, int& x2, int& y, int& z)
{
   int maxX, maxY, maxZ, dump;
   m_ImageStencilData->GetExtent(dump, maxX, dump, maxY, dump, maxZ);

   bool gotExtent = false;
   while (!gotExtent)
   {
     gotExtent = m_ImageStencilData->GetNextExtent(
       x1, x2, 0, maxX, m_Y, m_Z, m_Iter) > 0;

     if (!gotExtent) { m_Iter = 0; ++m_Y;  }
     if (m_Y > maxY) { m_Y = 0; ++m_Z; }
     if (m_Z > maxZ) { m_Z = 0; return false; }
   }

   y = m_Y; z = m_Z;// *y and z ???*
   return true;
}

Nil

Le 2015-04-30 12:55, David Gobbi a écrit :
> On Thu, Apr 30, 2015 at 9:53 AM, David Gobbi <david.gobbi at gmail.com 
> <mailto:david.gobbi at gmail.com>> wrote:
>
>     Hi Nil,
>
>     I wrote a stencil iterator that provides the x, y, and z indices
>     (not in VTK yet).  It still requires an image to iterate over, but
>     it might be worth a glance:
>     https://github.com/dgobbi/AIRS/blob/master/ImageSegmentation/vtkImageRegionIterator.h
>
>     In order for your GetNext() function to work as an iterator
>     function, it should not have any loops, just conditionals:
>
>     if ->GetNextExtent() returns zero, it should reset m_Iter to zero
>     and increment m_Y
>     if m_Y > maxY, it should reset m_Y to zero and increment m_Z
>     if m_Z > maxZ, it should reset m_Z to zero and return false
>
>
> I realized that it isn't quite as simple as what I wrote.  Everything 
> has to be in a loop, because it has to keep trying until it gets a 
> valid extent:
>
>   bool gotExtent = false;
>   while (!gotExtent)
>     {
>     gotExtent = m_ImageStencilData->GetNextExtent()
>     if gotExtent is zero, it should reset m_Iter to zero and increment m_Y
>     if m_Y > maxY, it should reset m_Y to zero and increment m_Z
>     if m_Z > maxZ, it should reset m_Z to zero and return false
>     }
>
> No guarantees, of course, since it's completely untested pseudocode.
>
>  - David
>
>
>     On Thu, Apr 30, 2015 at 8:54 AM, Nil Goyette <nil.goyette at imeka.ca
>     <mailto:nil.goyette at imeka.ca>> wrote:
>
>         Hi all,
>
>         I'm  using vtkPolyDataToImageStencil to get all voxels index
>         inside of a surface. If I understand correctly, I have only
>         two choices here:
>         - vtkImageStencil to create a new image
>         - vtkImageStencilIterator to iterate on the values (of another
>         image)
>         The problem is, I have a different goal in mind. I need the
>         index of all voxels inside a surface.
>
>         I read the vtkPolyDataToImageStencil code and tried to create
>         my own "iterator" but there's probably something I don't
>         understand; GetNextExtent always return 0.
>         bool GetNext(int& x1, int& x2, int& y, int& z)
>         {
>           // m_Y, m_Z and m_Iter == 0
>           int maxX, maxY, maxZ, dump;
>         m_ImageStencilData->GetExtent(dump, maxX, dump, maxY, dump, maxZ);
>           maxX *= 2; maxY *= 2; maxZ *= 2;
>
>           for ( ; m_Z <= maxZ; ++m_Z)
>           {
>             for ( ; m_Y <= maxY; ++m_Y)
>             {
>               if (m_ImageStencilData->GetNextExtent(x1, x2, 0, maxX,
>         m_Y, m_Z, m_Iter))
>               {
>                 y = m_Y; z = m_Z;
>                 return true;
>               }
>             }
>           }
>           return false;
>         }
>
>         Is there a way to access all inside-voxels hidden in the
>         vtkPolyDataToImageStencil? By index or by index range, it's
>         not important. I just want to know to access them without
>         useless work (like creating an image) because it's gonna be
>         called often; it needs to be fast. Thank you for your time.
>
>         Nil
>
>
>

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