Find coordinates inside a matrix with specific conditions

Question

Alberto Acri 2024-1-17

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2071251-find-coordinates-inside-a-matrix-with-specific-conditions

编辑： Matt J 2024-1-17

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')

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Matt J 2024-1-17

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 2024-1-17

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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Answer 1

Matt J 2024-1-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2071251-find-coordinates-inside-a-matrix-with-specific-conditions#answer_1391856

编辑：Matt J 2024-1-17

在 MATLAB Online 中打开

Using this FEX download,

https://www.mathworks.com/matlabcentral/fileexchange/87584-object-oriented-tools-for-fitting-conics-and-quadrics

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