[Insight-developers] level sets: curvature term and time step

[Joshua Cates]

Hi Lydia,

Just to clarify: you are talking about the spatially varying curvature 
term, and not the curvature calculation itself? So only filters 
which use this term should be affected, right?

Josh.

______________________________
 Josh Cates			
 School of Computer Science	
 University of Utah
 Email: cates at sci . utah . edu
 Phone: (801) 587-7697
 URL:   http://www . sci . utah . edu/~cates


On Thu, 10 Jul 2003, Lydia Ng wrote:

> 
> Question for those interested in level sets:
> 
> Currently the itk::LevelSetFunction class does not take the curvature
> term into account when computing the time step to meet the CFL criterion
> to ensure numerical stability.
> 
> This is causing some grief with users playing around with the scaling
> parameter in each of the term in particular when they set the curvature
> scaling to be high relative to the propagation and advection terms.
> 
> Can someone point me to a paper/book that talks about have to compute
> the CFL time step for the curvature term? 
> 
> Alternatively, (hacking versus mathematically sound) could we just
> restrict the time step such that the change in level set value due to
> the curvature term is no larger that half a pixel? Would this have the
> desired affect?
> 
> The second alternative is for me to change my filters
> ShapeDetectionLevelSetImageFilter and
> GeodesicActiveContourLevelSetImageFilter just to use a constant time
> step - making it the user's problem to ensure they choose the time step
> small enough. This is how it was before, when I got complaints from
> other users about how it was difficult to set this parameter...
> 
> Cheers,
> Lydia
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