The counts for radius 0, 1, and 2 make sense to me. As I understand you,
pyMVPA follows a "faces must touch" rule: each increase in radius is
done by adding all the voxels that share at least face with the previous
radius.
But I figure 86 voxels surrounding the center for a radius three
searchlight, not 122. I posted pictures at:
http://mvpa.blogspot.com/2012/09/pymvpa-searchlight-shapes.html
Jo
On 9/11/2012 1:52 AM, Michael Hanke wrote:
On Tue, Sep 11, 2012 at 08:49:09AM +0200, Michael Hanke wrote:
On Mon, Sep 10, 2012 at 11:21:02AM -0700, Jonas Kaplan wrote:
Seems to me that radius of 1 gives 7 voxels, e.g.:
In [117]: radii = range(5)
In [118]: for radius in radii:
.....: sp = Sphere(radius=radius)
.....: size = len(sp((1,1,1)))
.....: print "Radius %d size: %d" % (radius,size)
.....:
Radius 0 size: 1
Radius 1 size: 7
Radius 2 size: 33
Radius 3 size: 123
Radius 4 size: 257
Thanks Jonas!
In PyMVPA >= 0.6 voxel neighbors are elements that share an edge
(not just a corner), hence 7 elements for radius=1 (2 elements per axis
and the center). radius=0 will select just the center.
Err, the need to share _two_ edges, not just one.
--
Joset A. Etzel, Ph.D.
Research Analyst
Cognitive Control & Psychopathology Lab
Washington University in St. Louis
http://mvpa.blogspot.com/
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