Creating a spherical matrix

I am attempting to run a monte carlo simulation modeling the photon transport in a sphere with two different layers. To run this code I need to generate a segmented sphere. The 100x100x100 slab example with four different layers looks like this:

seg = zeros(100,100,100);
seg(:,:,10:25) = 1;
seg(:,:,26:50) = 2;
seg(:,:,51:75) = 3;
seg(:,:,76:end) = 4;
fid = fopen('seg.bin', 'wb');
fwrite(fid, seg, 'uint8');
fclose(fid);

How would I do something similar for a 50x50x50 sphere and an ellipsoid. The commands sphere() and ellipsoid() give me the coordinates for such a shape in an array, but I need to assign numbers as in the example above to a spherical volume.

Thank you so much!

Answer 1

[Teja Muppirala]

Something like this?

Rx = 1; %<-- Change these to make an ellipse instead
Ry = 1; %<-- Change these to make an ellipse instead
Rz = 1; %<-- Change these to make an ellipse instead

[X,Y,Z] = ndgrid(linspace(-Rx,Rx,50),linspace(-Ry,Ry,50),linspace(-Rz,Rz,50));

R = sqrt((X/Rx).^2 + (Y/Ry).^2 + (Z/Rz).^2);

seg = zeros(size(X));
seg(R <= 1 ) = 1;
seg(R <= 0.5) = 2;

slice(Y,X,Z,seg,0,0,0);
axis equal vis3d; colorbar;

[Julia Sandell]

Thank you so much! This exactly what I needed!

[Chen]

Hi Teja,

is there anyway to make an ellipsoid insteand of a perfect sphere? I tried to change Rx, Ry and Rz, but it turns out I always get the same sphere...? Can you give an example?

Thanks in advance!!