MATLAB: Get data within circular ROI

circular roicoordinates in roidata points within roi

Hi,
I have a 2D mesh of datapoints (200×200 coordinates) that I've called plot_data. I have drawn a circular ROI on the mesh and want to extract all the coordinates within this circle.
The circle has been drawn as the following, where x and y are the coordinates that I've extracted for the line that is the circle:- 
        theta = linspace(0,360);
        radius = 20 %circle radius
        centre = [100,100] %circle centre
        y = radius*sind(theta)+centre(2); 
        x = radius*cosd(theta)+centre(1);
        c = plot(x,y,'k'); %draw circle
How would I get all the datapoints within this circle please?
Thanks!

Best Answer

This code also works for non-integer positions and radii.
data=rand(200,200); %generate example data
radius = 20; %circle radius
centre = [100,100]; %circle centre
[X,Y]=ndgrid(1:size(data,1),1:size(data,2));
X=X-centre(1);Y=Y-centre(2);%shift coordinate grid
L=sqrt(X.^2+Y.^2)<=radius;
data_within_circle = data(L);
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