Order List of Neighbors In Counter Clockwise Fashion

Hello,

I am trying to generate the natural neighbors of all points in my data set here I have what I am currently doing for one point.

for i=1:3
    for j=1:nt
        if t(j,i)==5
            nn(j,:)=t(j,:);
        end
    end
end
nn = nn(any(nn,2),:);
nn = unique(nn);
nn = nn(find(nn~=5));

Where t is the delaunay triangulation which is essentially acting as a connectivity list.

This yields the natural neighbors of point number 5 in the data set which I just picked 5 arbitrarily. What I would like is for it to order the coordinates in a counter clockwise manner going around point 5. Like this image:

From there I can compute this same thing for all data sites. Is there also a better way to compute this without the nested for loops I am running to search the Delaunay triangulation?

Thanks

Answer 1

[darova]

Yes, there is one! Look, just get angle of each point and sort it

clc,clear

r = 2+rand(20,1);
t = rand(20,1)*2*pi;
[x,y] = pol2cart(t,r);
[~,ix] = sort(t);
plot(x(ix),y(ix),'.-r')
line(x,y)