[Insight-users] blob with polyline path boundary

[Dan Mueller]

Hi Tomáš,

On 17/11/2007, Tomáš Kazmar <Tomash.Kazmar at seznam.cz> wrote:

> I need to represent a blob-like structure which I understand can be achieved
> in ITK by BlobSpatialObject. That is ok but apart from that I need to traverse
> blob's boundary as a closed curve. To be precise knowing contour pixels is not
> enough, I have to know how these pixels are ordered as well.  Is there any way
> to do that?

Are you referring to 2-D contours only, or 3-D surfaces as well? How
exactly do you need to order / traverse the points?

Assuming you mean 2-D contours only, it may be possible to order the
points using the Fast Marching filter. This filter expects a speed
function (a binary version of your contour, 0.0 outside the contour,
1.0 on the contour) and an initial seed. A front will expand from the
seed point (in both directions) assigning an increasing (real valued)
arrival time to each point on the contour. It may be possible to
conceive a way to then track from the largest arrival time back to the
seed, and continue around from the seed to the largest value, thus
ordering the points on the contour. Just a thought... I'm not aware of
any other methods in ITK which provide an explicit solution to your
problem (although I'm not exactly an expert in these matters).

Anyway, hope this helps.

Cheers, Dan