Produce a 3D stem plot with a custom colormap in MATLAB

Question

I have a matrix (200 x 4) where first 3 values are X, Y and Z data. I want use the fourth column to display each (X,Y,Z)

Answer 1

You can use HSV as well. The Z values would correspond to your fourth column. Low Z values are blue and high Z values are red.

I used the site http://colorizer.org/ to work out that blue is H=0.65 and red is H=1. S and V stay the same.

From http://colorizer.org/, I got that a blue colour is H=236, S=100, V=100. Then the H value for blue is H = 235/360 = 0.65 and H=1, S=1, V=1 for red.

---

num_elem = 200;
c = linspace(0,1,num_elem)'; % // Replace this with the values from your fourth column


% // The equation gives blue (H=0.65) for c=0 and red (H=1) for c = 1
H = 0.65 + ((1-0.65).* c); 
S = ones(size(c,1),1);
V = ones(size(c,1),1);

% // You have to convert it to RGB to be compatible with stem3

colourmap = hsv2rgb([H,S,V]);


% // Generate some sample data
theta = linspace(0,2*pi,num_elem)';
X = cos(theta);
Y = sin(theta);
Z = theta;

% // Plot the sample data with the colourmap
figure;
hold on;
for idx=1:num_elem
  stem3(X(idx),Y(idx),Z(idx),':*','Color',colourmap(idx,:) ...
  ,'MarkerEdgeColor',colourmap(idx,:) ...
  ,'MarkerFaceColor',colourmap(idx,:) ...
  ,'LineWidth',4 ...
  );
end

hold off;
set(gca,'FontSize',36');