Drawing upside down cone using spherical coordinates.

I wrote the following code:

phi=pi/6; 
theta=linspace(0,2*pi,63); %Theta goes from 0 to 2*pi.
a=linspace(0,1,21);
[PHI,THETA,A]=meshgrid(phi,theta,a); 

X=A.*sin(PHI).*cos(THETA); % Spherical coordinates
Y=A.*sin(PHI).*sin(THETA); 
Z=A.*cos(PHI); 

surf(X,Y,Z)
axis equal

It won't draw, but instead gives me an empty 2D graph.

The error message is:

Error using matlab.graphics.chart.primitive.Surface

Value must be a vector or 2D array of numeric type.

Error in surf (line 145)

hh = matlab.graphics.chart.primitive.Surface(allargs{:});

Answer 1

[Benjamin Kraus]

The issue you are facing is that when you call meshgrid you are specifying three input vectors, so the output matrices are going to be 3D matrices, but surf only accepts 2D matrices.

My recommendation is to remove phi from the call to meshgrid:

phi=pi/6; 
theta=linspace(0,2*pi,63);
a=linspace(0,1,21);
[THETA,A]=meshgrid(theta,a); 
X=A.*sin(phi).*cos(THETA);
Y=A.*sin(phi).*sin(THETA); 
Z=A.*cos(phi); 
surf(X,Y,Z)
axis equal

[Viktor Karlsson]

Thank you so much for taking the time to help, works like a charm!