I want to extract a circle of values from a meshgrid

I have a 2D meshgrid with dimensions of distance x distance. I want to know the values at a fixed radius from the center.

Answer 1

[Ameer Hamza]

What do you need value from mesh grid, you can calculate the points on the perimeter of the circles using pol2cart(). For example

r = 1
[x,y] = pol2cart(linspace(0, 2*pi, 100), r)

will give you x, y coordinates of points in the circle of radius r.

Edit: If you want to find the points from the mesh grid, then the following code can help

x = -5:1:5;
y = -5:1:5;
[X Y] = meshgrid(x,y);

r = 3; % radius
tolerane = 2;

indicator = abs(X.^2 + Y.^2 - r^2) < tolerane;

xCircle = X(indicator);
yCircle = Y(indicator);

Since points on the grid are discrete you will need to define a tolerance to for accepting a point. You will need to tune the tolerance parameter according to the resolution of your grid to get all points on the circle.

[Justin Dubin]

I want to extract the value of each grid box in the imagesc plot (see attached) that falls under the red circle.

[Ameer Hamza]

See the updated answer.

[Justin Dubin]

Yes, this does the job just fine. Thank you, Ameer!

[Ameer Hamza]

You are welcome.

Answer 2

[Image Analyst]

You might like to look at the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F