How to calculate the diameter of 3D Gaussian normal distribution?

I want to calculate the diameter of this gaussian distribution. Is there any simple mean to do so?

Answer 1

[KSSV]

Let X, Y,Z be your matrices.

val = 0.5 ;   % at this z-value I want radius / diameter 
idx = abs(Z-val) < 10^-3 ; 
x = X(idx) ; y = Y(idx) ; z = Z(idx) ; 
C = [mean(x) mean(y)]  ;   % Center of circle 
dx = C(1)-x ; 
dy = C(2)-y ; 
R = sqrt(dx.^2) ;
D = 2*mean(R);

Also you can try fitting a circle with the obtained (x,y) using https://in.mathworks.com/matlabcentral/fileexchange/5557-circle-fit

[Muhamed Sewidan]

Thank you