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

[lynx.abraxas at freenet.de]

Hello again!


With  Luis  answer  I  remebered seing such thing some where in the vtk books.
Having had a longer look for that again  I  came  up  with  all  these  for  a
possible realization:


sphere/ellipsoid sources:

vtkSphere:                      impicit function
vtkSphereSource:                a mesh of a sphere (theta, phi)
vtkImageEllipsoidSource:        a filled sphere/ellipsoid image


Possible ways to create an image of a sphere surface:

- by "hand": vtk book p.152
- vtkSphere -> vtkSampleFunction -> threshold at 0 ?
- vtkImageEllipsoidSource - vtkImageEllipsoidSource (r1 < r2)
- vtkSphereSource -> vtkImplicitModeller or vtkVoxelModeller ?


So  I  now wonder what would be the best way to get exact 6|26 connectivity or
an anti-aliased result that is best for masking a reagion that would  be  just
the 2D spere surface if there wouldn't be the dicretisation.

Since  I'm  using  itk  and  vtk  for my project what would be better (running
quicker) for this task an itk or a vtk implementation?


Thanks for any help or hints
Lynx

On 13/02/10 12:53:27, 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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