# Plot projection points after PCA analysis

4 views (last 30 days)
monkey_matlab on 22 Oct 2016
Answered: Image Analyst on 22 Oct 2016
I have these simple points:
X = [-0.7142;-1.7142;-1.7142;-0.7142;1.2857;1.2857;2.2857];
Y = [1.2857;0.2857;-0.7142;0.2857;0.2857;-0.7142;-0.7142];
I then found the projected points (using PCA) as
X_proj = [-2.2316; 0.0648; 1.044; -0.2725; -2.1535; 1.7647; 1.2005];
Y_proj = [2.8746; 3.4734; 1.5356; 1.5142; -2.4040; -1.4030; -2.3826];
I found the PCA axis as:
y1 = 0.2053*x1 + 0;
y2 = -0.48719*x2 + 0;
How can I show these points graphically on the two different planes?
Thanks.
monkey_matlab on 22 Oct 2016
Hello, How do I go about showing the original points and then the projected points on two different planes? Although the attached image is a little degraded, there are two planes: Do I have to use a 3D plot then?

Image Analyst on 22 Oct 2016
(Regarding the image you added to clarify the post...) Why do you want them on different planes? Personally I think having two different marker shapes is fine. You could even give them different colors if you want. But I think plotting in 3D would just unnecessarily complicate it. But if you insist, you can do it with plot3()
clc; % Clear the command window.
close all; % Close all figures (except those of imtool.)
%clear; % Erase all existing variables. Or clearvars if you want.
workspace; % Make sure the workspace panel is showing.
format short g;
format compact;
fontSize = 20;
x1 = 4*rand(1, 6) - 2;
y1 = 4*rand(1, 6) - 2;
x2 = 4*rand(1, 6) - 2;
y2 = 4*rand(1, 6) - 2;
% Plot set 1 as red * at plane z=0
z1 = zeros(1, length(x1));
plot3(x1, y1, z1, 'r*', 'MarkerSize', 8, 'LineWidth', 2);
% Plot set 2 as blue circles at plane z=1.5
z2 = 1.5 * ones(1, length(x2));
hold on; % Don't blow away set #1!
plot3(x2, y2, z2, 'bo', 'MarkerSize', 8, 'LineWidth', 2);
grid on;
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
zlabel('Z', 'FontSize', fontSize); Image Analyst on 22 Oct 2016
What is wrong with plot()?

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