# Radially plot ROIs on image

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Russell Chow on 2 Oct 2021
Commented: Russell Chow on 3 Oct 2021
I have a 64x64 rectangular ROI. I want to place 30 of them in a radial pattern from a set distance from the center of my image. I will then calculate take the FFT of these ROI regions. I can't seem to figure our how to plot the ROIs in a radial pattern. Any starting tips would be greatly appreciated! Let me know if I need to provide more details. Example of what I would like below. KSSV on 2 Oct 2021
What data you have?

Simon Chan on 2 Oct 2021
Try using function cart2pol, following is an example
clear; clc;
Ny = 1000;
Nx = 1000;
Nz = 30; % Number of ROIs
rho = 200; % Radius, 200 pixels
theta = linspace(-pi,pi,Nz); % Theta separation
cx = 400; % Your center point, x-coordinates = 400 (example)
cy = 700; % Your center point, y-coordinates = 700 (example)
[x,y] = pol2cart(theta,rho); % Use pol2cart
cx_coord = round(cx-x); % Convert back from polar coordinates
cy_coord = round(cy-y);
ROIsize = 64; % Size of ROI
x1 = round(cx_coord - ROIsize/2); % x start position
x2 = x1 + ROIsize - 1; % x end position
y1 = round(cy_coord - ROIsize/2); % y start position
y2 = y1 + ROIsize - 1; % y end position
plot(cx, cy,'g*');
hold on
for k = 1:Nz
plot(cx_coord, cy_coord, 'b.')
plot([x1(k),x2(k),x2(k),x1(k),x1(k)],[y1(k),y1(k),y2(k),y2(k),y1(k)],'r-');
end
xlim([0 Nx])
ylim([0 Ny]) Russell Chow on 3 Oct 2021
@Image Analyst I have a quick question. i created a mask of the roi and i want to take the FFT of this section, however due to the mask, all my values in the roi are just 1. how can i use the pixel values in the roi without making them binary?