How to change radial tick markers in Matlab polar plot? - matlab

Question

I'd like to relabel the radial tick markers in the following polar log plot:
f = figure ;
t = 0:0.01: pi/2 ;
polar(t, 10 * log10(cos(t))/(50) + 1)
from 1, 0.8, 0.6, 0.4, 0.2 to 0, -10, -20, -30, -40 (i.e. radial dB ticks).
Trying some of the methods from Fixing the Radial Axis on MATLAB Polar Plots, I was able to relabel the markers provided my tick markers were positive and increasing.
I tried the following based on How to remove Rho labels from Matlab polar plot?
rho_labels = {'1' '0.8' '0.6' '0.4' '0.2'};
rho_labels2 = {'0' '-10' '-20' '-30' '-40'};
for r=1:length(rho_labels)
ff = findall(f, 'string', rho_labels{r}) ;
ff = rho_labels2{r} ;
end
but it also didn't work (seems to do nothing, so I suspect I'm operating on a copy of the find results not handled).
How can these tick markers be adjusted? Also, if I wanted a different number of concentric circles than 5, how can that be done (for example, 4 subdivisions with -40 dB at the "origin".)

Answer 1

Here is a way to rename the radial tick labels. Be warned that if there is a match between any radial and angular tick mark labels, both will be replaced and the angular labels will be wrong. But the angular tick labels are fixed as 0, 30, 60, ..., 330, so as long as the radial tick labels don't include these values, you should be fine.
What the code does is find all the text in the plot using findall, trim the blank spaces at the front of each string, then, for each entry in rho_labels, set the string entry corresponding to the tick label with that identifier to the corresponding entry in rho_labels2.
f = figure ;
t = 0:0.01: pi/2 ;
polar(t, 10 * log10(cos(t))/(50) + 1)
rho_labels = {'1' '0.8' '0.6' '0.4' '0.2'};
rho_labels2 = {'0' '-10' '-20' '-30' '-40'};
ff = findall(f,'type','text');
t=strtrim(get(ff,'String'));
for r=1:length(rho_labels)
set(ff(strcmp(t,rho_labels{r})),'String',rho_labels2{r})
end
To modify the number of rings, I think think of anything better than modifying polar.m and creating your own custom polarMOD.m function. If you do this you can also do the radial labels as well. In fact, there might be such a function on the MathWorks File Exchange.