# Find coordinates inside a matrix with specific conditions

조회 수: 5 (최근 30일)
Alberto Acri 2024년 1월 17일
편집: Matt J 2024년 1월 17일
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')
##### 댓글 수: 2없음 표시없음 숨기기
Matt J 2024년 1월 17일
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?
Alberto Acri 2024년 1월 17일
Hi Matt! The nodes to be searched must be in 'plane_new_ok.mat'. Starting from any node in 'plane_new_ok.mat' (node A), I must find the other two nodes (B and C) arranged at approximately (or ugual) 90°!

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### 채택된 답변

Matt J 2024년 1월 17일
편집: Matt J 2024년 1월 17일
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')
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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