@Alberto Acri, I don't have the toolbox you do but you should be able to expand Rowsx3 similar to this (red are added):
% Create an example Rowsx3
[x,y,z] = sphere(60);
i = randperm(length(x(:)));
Rowsx3 = [x(i)' y(i)' z(i)'];
% Find nearest neighbors
d2d = (Rowsx3(:,1)-Rowsx3(:,1)').^2+(Rowsx3(:,2)-Rowsx3(:,2)').^2+(Rowsx3(:,3)-Rowsx3(:,3)').^2;
d2d(d2d(:)==0) = nan;
[d2dm,d2di] = min(d2d);
% If want 75x75 = 5625 instead of 3721 (61x61)
k = (75^2-length(Rowsx3));
% Choose mean of random nearest neighbors for cloud growth
ei = randperm(length(Rowsx3),k);
Rowsx3e(:,3) = mean([Rowsx3(d2di(ei),3) Rowsx3(ei,3)],2);
Rowsx3e(:,2) = mean([Rowsx3(d2di(ei),2) Rowsx3(ei,2)],2);
Rowsx3e(:,1) = mean([Rowsx3(d2di(ei),1) Rowsx3(ei,1)],2);
% Plot original as blue and extension as red (red are added)
figure
plot3(Rowsx3(:,1),Rowsx3(:,2),Rowsx3(:,3),'b.',Rowsx3e(:,1),Rowsx3e(:,2),Rowsx3e(:,3),'r.')
axis square; axis equal
As for reducing Rowsx3 just removing some of the nearest neighbors should work as well (red are removed):
% . . .
% If want 50x50 = 2500 instead of 3721 (61x61)
k = (50^2-length(Rowsx3));
% Choose random nearest neighbors for cloud reduction
ei = randperm(length(Rowsx3),-k);
Rowsx3r = Rowsx3;
Rowsx3r(ei,:) = [];
% Plot original as red and remaining as blue (red are removed)
figure
plot3(Rowsx3(:,1),Rowsx3(:,2),Rowsx3(:,3),'r.',Rowsx3r(:,1),Rowsx3r(:,2),Rowsx3r(:,3),'b.')
axis square; axis equal
