How to represent a grid circle in a plane?

Question

My idea here is to represent temperature in a plane circle divided in polar coordinates (grid) using colours, as the plot axis will only show the geometry dimensions.

That's what I have so far.

[R,THETA] = meshgrid(linspace(0,r,nr),linspace(0,theta,ntheta)*(pi/180));
[X,Y] = pol2cart(THETA,R);    
contourf(X,Y,T,10);

The main issues here are that awful line and the absence of the theta grid.

And that's the kind of grid that I'm looking for, but inside of a single plane.

The code:

r = 0.05; % Radius (m)
dr = 0.0025; % Element Size R (m)
nr = r/dr+1; % Number of Elements R
rc = (nr-1)/2+1; % Central Element R

theta = 360; % Degrees (°)
dtheta = 5; % Elezement Size Theta (°)
ntheta = theta/dtheta+1; % Number of Elements Theta

[R,THETA] = meshgrid(linspace(0,r,nr),linspace(0,theta,ntheta)*(pi/180));

[X,Y] = pol2cart(THETA,R);

T1 = 10;
T2 = 50;

dT = T2-T1; % dTemperature

for i = 1:73
    T(i,:) = T1:dT/(nr-1):T2; % Temperatura Distribution
    %T(i,:) = T(i,:) * i*0.5;
end

contourf(X,Y,T,10);

Thank you in advance.

please share your WHOLE code so we can reproduce your problem — Benoit_11, Nov 25 '15 at 14:09
@GameOfThrows It works, but how do I add color to that? I need it to look like the first graph here. Thank you! — Vitor Ramalho, Nov 25 '15 at 14:29
take a look at Mathwork's help page on `mesh` http://uk.mathworks.com/help/matlab/learn_matlab/creating-mesh-and-surface-plots.html?refresh=true you should be able to figure it out, it involves basically imposing your plot onto the mesh object. — GameOfThrows, Nov 25 '15 at 14:48

lhcgeneva · Accepted Answer · 2015-11-25T16:57:40.093

3

Not sure it's easiest to use mesh here. Why not just plot the lines, similar to what's done in MATLAB's built-in polar():

N_half = 12;
th = (1 : N_half) * 2 * pi / (2 * N_half);
cst = cos(th);
snt = sin(th);
cs = [-cst; cst];
sn = [-snt; snt];
line(r * cs, r * sn, 'Color', 'k');
axis 'square'

gives

where N_half modifies how many lines you are plotting.

edited Nov 25 '15 at 16:57

answered Nov 25 '15 at 16:01

lhcgeneva

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That solved my problem perfectly! Nice and simple! Do you know the reason for that black line in the right portion of the circle? It keeps showing up! – Vitor Ramalho Nov 26 '15 at 13:40
Does it still show up? If I run the last bit of your code and mine immediately afterwards I don't see the black line. – lhcgeneva Nov 26 '15 at 13:44
Running the same here and showing up. It must be something related to my settings on this computer, idk. Thank you anyway! Just found another option using "pcolor(X,Y,T);", but I'll keep it simple like this. – Vitor Ramalho Nov 26 '15 at 13:50
But if you constrain your axis to a square as done above, you shouldn't see anything black, because it's not within the visible part of the graph, or am I missing something here? Glad I could help anyway! – lhcgeneva Nov 26 '15 at 13:52
@VitorRamalho The issue with the unwanted black line [**is adressed here**](http://stackoverflow.com/questions/28239826/removing-the-edge-line-on-a-contour-plot). – Robert Seifert Nov 27 '15 at 07:06
Thank you, @thewaywewalk. Very useful. – Vitor Ramalho Nov 27 '15 at 14:48

How to represent a grid circle in a plane?

1 Answers1