How to get 3D Points of separate regions obtained from alphaShape?
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Taking example from MATLAB docs regarding alphaShape:
[x1, y1, z1] = sphere(24);
x1 = x1(:); y1 = y1(:); z1 = z1(:);
x2 = x1+5; P = [x1 y1 z1; x2 y1 z1];
% if you plot 'P' you'll see two spheres
% plot3(P(:,1),P(:,2),P(:,3),'.')
P = unique(P,'rows');
shp = alphaShape(P(:,1),P(:,2),P(:,3),1);
N = numRegions(shp)
Output:
N = 2
I am interested in finding which points of P belong to which region. In other words labeling points in P. This can be done using different clustering methods, but I would like to know if it is possible with alphaShape.
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Sean de Wolski
am 8 Apr. 2016
You can pass RegionID into alphaTriangulation. Loop over the region ids to grab the triangulations.
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Sean de Wolski
am 12 Apr. 2016
That looks right to me and matches the expectations for set intersection, i.e. no points in both but all points represented:
>>intersect(idx1,idx2)
ans =
Empty matrix: 0-by-1
>> all(ismember(alphaTriangulation(shp),union(idx1,idx2)))
ans =
1 1 1 1
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