How to draw a semi circle filled with jet color (like in the image) ?

Answer 1

[Star Strider]

Try this —

N = 250;
th1 = linspace(pi, 3*pi/2, N);
r = linspace(0, 1, N);
z = r;

x1 = r(:)*cos(th1);
y1 = r(:)*sin(th1);
z1 = r(:)*ones(1,N);

figure
surf(x1,y1,z1, 'EdgeColor','none')
axis('equal')
colormap(jet(N))
view(0,90)
xtxt = linspace(min(xlim), max(xlim), 4);
text(xtxt, ones(1,4)*max(ylim), compose('$%2d^{\\circ}$',[15 10 5 0]), 'Vert','bottom', 'Horiz','right', 'FontSize',15, 'Interpreter','latex')
Ax = gca;
Ax.Visible = 'off';

N = 250;
th2 = linspace(pi/2, 3*pi/2, N);
r = linspace(0, 1, N);
z = r;

x2 = r(:)*cos(th2);
y2 = r(:)*sin(th2);
z2 = r(:)*ones(1,N);

figure
surf(x2,y2,z2.', 'EdgeColor','none')
axis('equal')
colormap(jet(N))
view(0,90)
axis('padded')
Ax = gca;
Ax.Visible = 'off';
text(1.2*cos([3 2 1]*pi/2), 1.2*sin([3 2 1]*pi/2), [1 1 1], {'$\frac{3\pi}{2}$', '$\pi$', '$\frac{\pi}{2}$'}, 'Interpreter','latex', 'FontSize',26, 'Horiz','right', 'Vert','middle')

Make appropriate changes to get the desired result.

EDIT — Corrected typographical errors.

.

Answer 2

[Image Analyst]

See my attached colorwheel demo. You can vary things like inner and outer radius, number of colors, etc.