Finding locations on a graph (1x1x1 cube) and replacing values with zero

Hi all!

I have created this cube with 1000 random points within it:

 for i=1:1000

    x(i)=rand;
    y(i)=rand;
    z(i)=rand;

     scatter3 (x,y,z,'r');

Now what I need to do is define an area from the centre (centre point being 0.5,0.5) and give them these with 0 values/erase the values within that area.

It isn't the visual side that is important as it is the remaining values that I will be using the chart below is just a way of making it visually make sense!

So what I need is that everything between radius 0.5-0.7 = 'value 1', and radius 0.7-1.0 = value 2

Answer 1

[Baltam]

    % Do not use for loops, you can make a vector of random values in one
    % go.
    x=rand(1000,1);
    y=rand(1000,1);
    z=rand(1000,1);

    % Define centerpoint
    Cpt = [0.5 0.5 0.5];

    % Use definition of sphere x^2+y^2+z^2 < Radius^2
    % I used two logical statements and used a pointwise product. Similar
    % to an && statement. After that you need to convert the values back to
    % logicals.
    Z1 = logical ( ((x-Cpt(1)).^2+(y-Cpt(2)).^2+(z-Cpt(3)).^2 > 0.5^2) .* ((x-Cpt(1)).^2+(y-Cpt(2)).^2+(z-Cpt(3)).^2 < 0.7^2) );
    Z2 = logical ( ((x-Cpt(1)).^2+(y-Cpt(2)).^2+(z-Cpt(3)).^2 > 0.7^2) .* ((x-Cpt(1)).^2+(y-Cpt(2)).^2+(z-Cpt(3)).^2 < 1^2) );
    % Ztot contains ones for all points within both spheres but not
    % for the values within a radius smaller than 0.5. You can use this to
    % plot only these values.
    Ztot = logical(Z1+Z2);

    % Assign values for certain conditions
    value1 = 10;
    value2 = 5;
    values = NaN(size(x));
    values(Z1) = value1;
    values(Z2) = value2;

    % Plot results
    scatter3(x(Ztot),y(Ztot),z(Ztot),[],values(Ztot)) 
    xlim([Cpt(1)-1 Cpt(1)+1])
    ylim([Cpt(2)-1 Cpt(2)+1])
    zlim([Cpt(3)-1 Cpt(3)+1])

Kind regards, Baltam

Answer 2

[Om]

Thank you so much! That is exactly what I needed.

So now I need to give a value to the parts that remain within the blank sphere.