how to get a mean Z value inside a certain area I set on a plot

I left the same question a long ago, but I haven't solved the problem yet.

I have a plot as below;

I'd like to get a mean value of all Z values in a paricular area I set on the plot, for example, in the white circle in the figure below;

I wish to know how to set a certain area (draw manually?) and get a mean of all Z values in the area.

Can anyone help me out with this?

I really appreciate your help in advance!

Attached is the original Matlab figure file.

[Adam]

If you have the image processing toolbox you can draw polygons using

doc Polygon

which also has a function

createMask

which can be used to extract the points inside that polygon, then you can take the mean in the obvious way.

[EcoBase]

Thank you heaps Adam!! It worked!!

Answer 1

[darova]

Use this

ind = (Y-65).^2 + (X-85).^2 <= 45^2;        % find indices inside a circle
N = sum(ind(:));                            % number of indices
Z1 = Z.*ind;                                % values inside a circle
meanValue = sum(Z1(:))/N;                   

[EcoBase]

Thank you so so much! easy and straightforward answer to my long-held problem!

[EcoBase]

Just one more question, sorry!

How can I count the number of values (or percentage of area) that are greater than, say 10, inside the circle?

Thank you in advance.

[darova]

Indices inside the circle:

ind = (Y-65).^2 + (X-85).^2 <= 45^2;        % find indices inside a circle

To use these indices:

N = sum( Z(ind)>10 );