# How to plot sphere in sphere coordinates?

6 views (last 30 days)
Niklas Kurz on 18 Oct 2020
Commented: Bruno Luong on 21 Oct 2020
I'm just trying to plot known sphere coordinates:
function sphere(r)
phi = linspace(0,2*pi);
theta = linspace(0,pi);
x = r*cos(phi).*sin(theta);
y = r*sin(phi).*sin(theta);
z = r*cos(theta);
plot3(x,y,z)
end
However this isn't doing the trick. What have I mathematically confounded?

J. Alex Lee on 19 Oct 2020
Your problem is not with conversion or plotting, but defining the coordinates that you want...
[phi,theta] = meshgrid(linspace(0,2*pi),linspace(0,pi));
Also if you didn't know:

Niklas Kurz on 21 Oct 2020
yea, but I wanted to go through the rough way ;)
You could have said additionally that I need to swap plot3(x,y,z) with mesh(x,y,z), but all in all you've been nudging me in the right direction. Thx
J. Alex Lee on 21 Oct 2020
sure thing. if you decide you don't want the rough way and you haven't seen it, check
[X,Y,Z] = r*sphere(n)
mesh(X,Y,Z)
% surf(X,Y,Z) % filled in faces
Also check out

Bruno Luong on 21 Oct 2020
function sphere(r)
phi = linspace(0,2*pi);
theta = linspace(0,pi).'; % first change
x = r*cos(phi).*sin(theta);
y = r*sin(phi).*sin(theta);
z = r*cos(theta)+0*phi; % second change, make z same-size 2d array as x and y
plot3(x,y,z);
end

J. Alex Lee on 21 Oct 2020
nice. might be confusing depending on the audience though :)
As a side note, I wish plot also supported "implicit expansion" so you don't have to make the second change. As long as we have committed to the silent syntax, why not go the full nine yards!
Niklas Kurz on 21 Oct 2020
What a hoot! Just one thing: what does
.'
stand for?
Bruno Luong on 21 Oct 2020
Click on .'