Using surf to represent a function with color.

Hi everyone, I would like to represent the magnitude of a function on a surface (hemisphere) using a color map. Here is my current attempt

r=22; %radius of sphere
phi=linspace(0,pi,30);
theta=linspace(0,pi,40);
[phi,theta]=meshgrid(phi,theta); %meshgrid of sphere
x=r*sin(phi).*cos(theta);
y=r*sin(phi).*sin(theta);
z=r*cos(phi); 
mesh(x,y,z)
hold on
theta = linspace(0,pi) 
R=1/22 % R=Rs/r (constant)
Bo=21000 %constants
Bmag = Bo*((R).^3).*((1+3*(sin(theta)).^2)).^0.5 %magnetic field function
surf(x,y,z,Bmag)

I then get the error message

 Warning: Error creating or updating Surface
 Error in value of property  CData
 Array is wrong shape or size

Does anyone have any idea how I could represent this?

Answer 1

[Walter Roberson]

Delete the theta = linspace(0,pi) that you are using to redefine theta.

[John Draper]

Thanks, that gives me a figure. But the hemisphere is all one color now. Is there any way to plot it such that you can see the variation in Bmag across the surface of the hemisphere?

[Walter Roberson]

Remove the mesh()

The default for mesh is to color by z, so your color values for that range the same as your z, -22 to +22. Then when you surf() with Bmag as the color values (about 1.97 to twice that), MATLAB still has to use a color interpolation range large enough to include the now-hidden mesh, but only a narrow range of values are present in the visible image so they map to a narrow range of visible colors.

By default surf() draws edges, and so outlines the mesh anyhow. You can turn off those edges with

surf(x, y, z, Bmag, 'edgecolor', 'none')