[vtkusers] [Insight-users] How to create/draw a sphere surface image mask with 26|6 connectivity?

[Luis Ibanez]

Hi Lynx,


You could use the following set of classes


    1) itkEllipseSpatialObject
    2) itkSpatialObjectToImageFilter
    3) itkSimpleContourExtractorImageFilter


With (1) you can create a Sphere of the proper size,
With (2) you can rasterize that sphere into a binary image mask
With (3) you can extract the contour of the binary image mask


The filter (3) allows you to select the "thickness" of
the contour. You do this by adjusting the value of the
neighborhood "Radius" parameter.


----------------


You will find source code guiding examples in

  Insight/Examples/Filtering/
         SpatialObjectToImage1.cxx
         SpatialObjectToImage2.cxx
         SpatialObjectToImage3.cxx

and

  Insight/Examples/Registration/
          ModelToImageRegistration1.cxx
          ModelToImageRegistration2.cxx


The basic declarations will look like:


  const unsigned int Dimension = 3;
  typedef unsigned char MaskPixelType;

  typedef itk::Image< MaskPixelType, Dimension > MaskImageType;

  typedef itk::EllipseSpatialObject< Dimension >    SpatialObjectType;

  typedef itk::SpatialObjectToImageFilter<
                              SpatialObjectType,
                              MaskImageType
                                >   SpatialObjectToImageFilterType;


This will generate a discrete structure ("aliased").


Anti-aliased versions could be produced in several
different ways, depending on what you plan to do
with the resulting contour.

Some of the options for anti-aliased versions are:

A)  Take the aliased contour and pass it as input
      to the itk::AntiAliasBinaryImageFilter

B) Use either one of the following distance map filters:

        * SignedDanielssonDistanceMapImageFilter
        * SignedMaurerDistanceMapImageFilter



   Please let us know if you run into any problems,


          Thanks


               Luis


----------------------------------------------------------------------------
On Sat, Feb 13, 2010 at 6:53 AM,  <lynx.abraxas at freenet.de> wrote:
> Hello!
>
>
> I  need  a  3D  mask of a sphere suface once with 26 connectivity, once with 6
> connectivity and once with aliasing (as a weighting mask).
> The mask should be a cube of size NxNxN where N is odd (corresponding to  some
> definit  physsical  size) such that the centre pixel of the cube should be the
> centre of the sphere with a physical radius of 1.
>
> I was thinking of doing it with a for loop over all indices of the mask volume
> but  there  I don't know how to realize the none aliased cases. The aliasing I
> think could be done by assigning a grey value corresponding  to  the  distance
> from  the  actual  radius-point  to  the  nearest voxel-centre. The grey value
> should be down at zero for a distance bigger than one voxel.
>
> Looking at the docs I found the ellipsoid spacial object but nothing about how
> to  "render"  that  into a 3D image and again no clue how to differentiate the
> three "rendering cases".
>
> How could that be done with ITK or VTK?
> Is there a way to implement also a surface thickness bigger than 1 voxel?
>
> Many thanks for any help or hints.
> Lynx
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