Generating color map for a 3d grid

I apologize if this question had been asked before, I couldn't find the solution I needed.

I have a 3d grid which I plot using Scatter3 function. Each point in the grid has a value, which I want to translate to a color, any ideas how I do that?

A simple example:

X = 1:10;
Y = 1:10;
Z = 1:10;
Values = rand(10,10,10);

Each point has a correlated value in the Values Mat.

I want to do scatter3(X,Y,Z) But also making each dot to have a color like in normal Jet where the Jet color map is between min(values) to max(values).

P.S. In my real application I have much more dots then the simple line I created for demonstration

I appreciate the help.

Answer 1

[Voss]

X = 1:10;
Y = 1:10;
Z = 1:10;
Values = rand(10,10,10);

% 16-color jet colormap
cmap = jet(16);
NC = size(cmap,1);

% set up thresholds for determining which Values get which color
min_value = min(Values(:));
max_value = max(Values(:));
thresholds = linspace(min_value,max_value,NC+1);
thresholds(end) = Inf; % set the uppermost threshold to Inf to avoid missing Values at max_value

% color_idx is indices into cmap
color_idx = zeros(size(Values));
for ii = 1:NC
    % Values between two adjacent thresholds ii and ii+1 will get color cmap(ii,:)
    color_idx(Values >= thresholds(ii) & Values < thresholds(ii+1)) = ii;
end

% grid for scatter plot
[XX,YY,ZZ] = ndgrid(X,Y,Z);
% scatter plot with marker '.' size 20 and colors cmap(color_idx,:)
scatter3(XX(:),YY(:),ZZ(:),20,cmap(color_idx,:),'.')

% set up and display colorbar for reference
set(gca(),'Colormap',cmap,'CLim',[min_value max_value])
colorbar

[kuku hello]

May I ask a question? Why the operand & works but && doesn't?

[Voss]

&& is only for comparing scalars. In this case, Values is an array, so Values >= thresholds(ii) and Values < thresholds(ii+1) are arrays, so & must be used instead.

Example:

x = magic(3)

x = 3×3

8 1 6 3 5 7 4 9 2

x >= 2 & x < 6

ans = 3×3 logical array
   0   0   0
   1   1   0
   1   0   1

x >= 2 && x < 6 % error

Operands to the logical AND (&&) and OR (||) operators must be convertible to logical scalar values. Use the ANY or ALL functions to reduce operands to logical scalar values.

[kuku hello]

Thank you very much!

[Voss]

You're welcome!