Question

I am able to create a 3D cone in MATLAB, but: does anyone know how to paint the cone so that it recreates the HSV color space? I know there is the command:

colormap hsv;

but how do I use it?

Thanks in advance.

Answer 1

I’m guessing you want to create a plot similar to the cone in the following Wikipedia image:

One way to do this is to plot your cone and texture map the surface with an image of the HSV color space. Here’s how you could do this:

% First, create a 100-by-100 image to texture the cone with:

H = repmat(linspace(0, 1, 100), 100, 1);     % 100-by-100 hues
S = repmat([linspace(0, 1, 50) ...           % 100-by-100 saturations
            linspace(1, 0, 50)].', 1, 100);  %'
V = repmat([ones(1, 50) ...                  % 100-by-100 values
            linspace(1, 0, 50)].', 1, 100);  %'
hsvImage = cat(3, H, S, V);                  % Create an HSV image
C = hsv2rgb(hsvImage);                       % Convert it to an RGB image

% Next, create the conical surface coordinates:

theta = linspace(0, 2*pi, 100);  % Angular points
X = [zeros(1, 100); ...          % X coordinates
     cos(theta); ...
     zeros(1, 100)];
Y = [zeros(1, 100); ...          % Y coordinates
     sin(theta); ...
     zeros(1, 100)];
Z = [2.*ones(2, 100); ...        % Z coordinates
     zeros(1, 100)];

% Finally, plot the texture-mapped surface:

surf(X, Y, Z, C, 'FaceColor', 'texturemap', 'EdgeColor', 'none');
axis equal

And you should get the following figure: