Data from polar plot into frequency domain???

Hi,

I have coordinates of boundary of a picture (x,y) converted into polar plot (theta,rho) and now I need to work with data rho in frequency domain. Could someone advise how to do it, please? Here is my code and pictures:

http://www.nahraj-obrazek.cz/?di=014245375032 and http://www.nahraj-obrazek.cz/?di=3142453758011

BW=im2bw(I);
BWH=imfill(BW,'holes');
BWE=edge(BWH,'canny');
boundaries=bwboundaries(BWE);
b=boundaries;
x=b(:,2);
y=b(:,1); 
% cartesian plot
X=x-mean(x);
Y=y-mean(y);
THETA=X;
RHO=Y;
[THETA,RHO]=cart2pol(X,Y);
% polar plot
RHO1=smooth(RHO,10); % smoothing data
plot(RHO1);

I need to analyze wave (max and min amplitude, wavelength) and I thought that it would be the best in frequency domain or not? And maybe I need apply fft for data..

Thanks in advance!