Find coordinates inside a matrix with specific conditions
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I need to identify 3 nodes (the green ones, but it can also be the blue ones) within a matrix that generates a "circle" in space.
The figure is just an example, the important thing is that one node (A) is above the centre node, node (B) is below, node (C) is to the left.
Any good ideas?
plane_new = importdata("plane_new_ok.mat");
node_new = importdata("node_new_ok.mat");
figure
plot3(plane_new(:,1), plane_new(:,2), plane_new(:,3), 'r.', 'Markersize', 15);
hold on
plot3(node_new(:,1), node_new(:,2), node_new(:,3), 'r.', 'Markersize', 15);
hold off
axis equal
xlabel('x')
ylabel('y')
zlabel('z')
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1593446/image.png)
2 Commenti
Matt J
il 17 Gen 2024
Are A,B,C to be selected from points actually present in plane_new_ok.mat, even if there is no subset of points that are at perfect 90 degree intervals?
Risposta accettata
Matt J
il 17 Gen 2024
Modificato: Matt J
il 17 Gen 2024
Using this FEX download,
plane_new = importdata("plane_new_ok.mat");
node_new = importdata("node_new_ok.mat");
[~,i]=max(plane_new(:,3)); %arbitrarioy choose A
A=plane_new(i,:);
rA=A-node_new; %A-axis
P=planarFit([plane_new;node_new]');
rn=P.normal*sign(P.normal(3)); %plane normal
rC=cross(rn,rA); %C-axis
C=nearestPoint(node_new,+rC,plane_new);
B=nearestPoint(node_new,-rA,plane_new);
figure
plot3(plane_new(:,1), plane_new(:,2), plane_new(:,3), 'r.', 'Markersize', 15);
hold on
plot3(node_new(:,1), node_new(:,2), node_new(:,3), 'r.', 'Markersize', 15);
plot3(A(1), A(2),A(3), 'b.', 'Markersize', 40);
plot3(C(1), C(2),C(3), 'g.', 'Markersize', 40);
plot3(B(1), B(2),B(3), 'k.', 'Markersize', 40);
hold off
axis equal
xlabel('x')
ylabel('y')
zlabel('z')
legend('Data','Center','A','B','C')
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1593476/image.png)
function G=nearestPoint(c,d,xyz)
d=d/norm(d);
s=(xyz-c)*d'>0;
xyz=xyz(s,:);
Dist=vecnorm(cross(xyz-c,repmat(d,height(xyz),1)),2,2);
[~,ipos]=min(Dist);
G=xyz(ipos,:);
end
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