# Determine the coordinates of the nodes forming the outermost circle

8 views (last 30 days)
Alberto Acri on 17 Jan 2024
Commented: Dyuman Joshi on 17 Jan 2024
Hi! How can I extract only the coordinates of the nodes forming the outermost circle? The nodes are located on radius R = 4!
nodes = importdata("nodes.txt");
figure
plot3(nodes(:,1),nodes(:,2),nodes(:,3),'b.','Markersize',15);
axis equal
xlabel('x')
ylabel('y')
zlabel('z')
Dyuman Joshi on 17 Jan 2024
If you need a general answer (considering the cases where the data points are not uniformaly spaced), using convhull would be the most fitting.
Alberto Acri on 17 Jan 2024
I will consider it!

Hassaan on 17 Jan 2024
nodes = importdata('nodes.mat');
R = 4;
% Calculate the distance of each node from the origin in the x-y plane
distances = sqrt(nodes(:,1).^2 + nodes(:,2).^2);
% Find the indices of nodes that are close to the radius R
% You may need to adjust the tolerance depending on the precision of your data
tolerance = 0.1; % Tolerance for the radius match
outermost_indices = find(abs(distances - R) < tolerance);
% Extract the coordinates of the outermost nodes
outermost_nodes = nodes(outermost_indices, :);
% Plot all nodes
figure;
plot3(nodes(:,1), nodes(:,2), nodes(:,3), 'b.', 'Markersize', 15);
hold on;
% Highlight the outermost nodes in red
plot3(outermost_nodes(:,1), outermost_nodes(:,2), outermost_nodes(:,3), 'r.', 'Markersize', 15);
% Set axis properties
axis equal;
xlabel('x');
ylabel('y');
zlabel('z');
% Print the coordinates of the outermost nodes
disp('Coordinates of the nodes forming the outermost circle:');
disp(outermost_nodes);
% If you want to print coordinates with a label:
for i = 1:size(outermost_nodes, 1)
fprintf('Node %d: (x, y, z) = (%.4f, %.4f, %.4f)\n', i, outermost_nodes(i, 1), outermost_nodes(i, 2), outermost_nodes(i, 3));
end
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It's important to note that the advice and code are based on limited information and meant for educational purposes. Users should verify and adapt the code to their specific needs, ensuring compatibility and adherence to ethical standards.
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Image Analyst on 17 Jan 2024
Can you get the coordinates as a list of (x,y) locations? If so, get the convex hull with convexHull or convhull
Dyuman Joshi on 17 Jan 2024
+1 for convhull as I mentioned in my comment.

Alan Stevens on 17 Jan 2024
Here's an alternative way:
nodes = importdata("nodes.mat");
figure
plot3(nodes(:,1),nodes(:,2),nodes(:,3),'b.','Markersize',15);
axis equal
xlabel('x')
ylabel('y')
zlabel('z')
r = 4;
theta = 0:2*pi/20:2*pi;
for i = 1:numel(theta)
x(i) = r*cos(theta(i));
y(i) = r*sin(theta(i));
z(i) = 3;
end
hold on
plot3(x,y,z,'ro','markersize',15)
view(0,90)

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