[vtkusers] vtkPolyDataToImageStencil

[David Gobbi]

Hi Nil,

I'm not sure what you mean by "what will they become".  Each time your
GetNext() method is called and returns "true", the values (x1, x2, y, z)
will define a horizontal line segment between (x1,y,z) and (x2,y,z).

Thanks for writing out the method in full.  Now that I see the code I think
it looks better if the last condition calls "break" instead of "return
false":

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; break; }
  }

  y = m_Y; z = m_Z;
  return gotExtent;
}

On Thu, Apr 30, 2015 at 11:54 AM, Nil Goyette <nil.goyette at imeka.ca> wrote:

>  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>
> 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>
>> 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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