[Insight-users] Timestep in ShapeDetectionLevelSetFilter

[Joshua Cates]

Hello Bjorn,

The time step is the delta-t found in the documentation of
http://www.itk.org/Doxygen/html/classitk_1_1FiniteDifferenceImageFilter.html.

The time step controls the speed at which the solution is allowed to
converge from one iteration to the next.  Time step is used to maintain
stability in the solution by limiting the maximum change that a voxel can
make in any one particular iteration.

Ideally, we set the time step at each iteration automatically based on the
maximum change value of any voxel in the image at that iteration (the
level-set solvers do this).  The time step must be low enough to keep the
solution stable, but should be high enough to keep the solution
progressing at a reasonable rate.

Currently, some filters automatically set the time step for you and some
do not.  I think the plan is to add automatic time step determination to
those filters which do not yet have them.

For ShapeDetectionLevelSetFilter, a time step above 0.25 will probably not
be stable.  For 3D volumes you might want to decrease this to 0.125.

Hope this helps,

Josh.

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


On Tue, 6 Aug 2002, Bjorn Hanch Sollie wrote:

> I've been doing some work with this filter and I've obtained some
> pretty good results with it.  Although I've found a set of parameters
> that works well, I don't really know yet what the timestep parameter
> does.  Can someone please explain to me exactly what this parameter is
> and how changing it affects the solution (and any additional details
> possibly needed in order to understand it properly)?
>
> Thanks in advance!
>
> -Bjorn
> --
> The History of the Universe
> Chapter 1: Bang!  Chapter 2: Sss...  Chapter 3: Crunch!
> The End
>
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