[Insight-users] Curvature in Level Set

[Sah Rayman]

I found some "wierd behavior" of the curvature
calculated in SegmentationLevelSetFunction. 

While I expect the curvature to be 0.0125 everywhere, 
the actual curvature has a mean of 0.0137 (which is
good), but a s.t.d of 0.4. In another words, when the
tangent circle is actually of radius 80, the
calculation tells me the radius is 2 or 1 at some edge
points, and even concave in some other points.

Is it true that there are errors in curvature
calculation in the range of my discription? Or, there
must be something wrong in my application?

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Here is what I do in the test.

Full image is 256x256, ground truth is a circle whose
radius is 80 pixels, initial is a 60-pixel-radius
circle with a same center.

I disabled advection, curvature term, and there are
only speed term. Speed is +1 inside my ground truth,
and -1 otherwise. In fact, curvature weight is 1e-6 to
enable the curvature calculation.

After 180 iterations, I observe the output of
ComputeMeanCurvature() for one iteration, and take
statistics.

The output segmentation matches well with my ground
truth.
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