select a circular region of data and find the average value in that region

Hi! I need to select a circular region knowing the center and the radius and find the average value in that region. I tried with the equation of a circle but it doesn't work..what i need to do? Thanks

Answer 1

[KSSV]

Read about inpolygon.

nx = 100 ; ny = 150 ; 
x = linspace(0,1,nx) ; 
y = linspace(0,1,ny) ; 
[X,Y] = meshgrid(x,y) ; 
Z = rand(nx,ny) ; 
% Circle
C = rand(1,2) ; 
R = 0.3 ; 

th = linspace(0,2*pi) ; 
xc = C(1)+R*cos(th) ; 
yc = C(2)+R*sin(th) ; 

% get points inside circle 
idx = inpolygon(X(:),Y(:),xc,yc) ; 
% GEt mean 
iwant = mean(Z(idx')) ;

figure
hold on
pcolor(X,Y,Z')
plot(xc,yc)
plot(X(idx),Y(idx),'.r')