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Alpha shape macro available

Posted by Jonathan Lake on Jul 13, 2014; 7:32pm
URL: http://imagej.273.s1.nabble.com/Alpha-shape-macro-available-tp5008701.html

Hello all,

I have written a ImageJ1 macro that computes the alpha shape for a given point selection. It works analogously to the “Convex Hull” command but can produce concave and hollow shapes depending on the particular point set and alpha value. The output is a composite selection of the alpha shape. Give it a try and let me know if it works for you.

Three known issues:

1 - Technically the alpha shape can contain isolated edges that are not part of a polygon. These are not calculated by this script because ImageJ lacks the ability to combine multiple line ROIs. Generally these isolated edges are not practically useful.
2 - The script gets slow and can take a few minutes to complete once the number of points exceeds 200 or so. Constructing the Delaunay triangulation is slow.
3 - The script uses the ROI manager and will clobber anything that is in there when it is called.

Script download: http://jonlake.com/download/Alpha_Shape.ijm

A description of alpha shapes: http://cgm.cs.mcgill.ca/~godfried/teaching/projects97/belair/alpha.html
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