How do i fill this cilinder matrix with ones

Hi,

I've an matrix of a cilinder but the "inside" isn't completely filled with ones and I need it for further purposes of the function. Does somebody have a way to do this?

if true

height = linspace(8.1280,0,20); 
radius = linspace(30,30.5,20); 
% Scale factor: number of pixels per mm, chosen gridsize on the base of calculation time 
% and accuracy of the graph - VOXELS
factor = 8;   
r     = radius.*factor;              
h     = height.*factor;   
%%Creation of flattening filter matrix:
% Creating an empty 3D array based on the size of the flattening filter
maxx  = round((max(r) + 10));               % Size of the volume (X-direction); maximum value of flattening filter radius is used. 
                                          % + 10 is to create more space, to have a volume sure big enough. 
maxy  = round((max(r) + 10));               % Size of the volume (Y-direction); Idem.      
maxz  = round((max(h) + 10));               
XmatrixFF = (2*maxx)+1;                     % Volume with variable size. The + 1 statement is for creating a centre point.
YmatrixFF = (2*maxy)+1;                     % The centre point is de collimator axis. Imagine the square field with a cross in it.
Rmax = ceil(sqrt(maxx.^2 + maxy.^2));        % creation of the radius, Rmax = srqt(x^2 + y^2)
R = (0:Rmax);                              % R = kolom vector van 0 tot Rmax
H = interp1(r,h,R,'linear');               % Connects the height points linearly, to find the corresponding height of  radius ri.      
[~,~,z]     = meshgrid(1:XmatrixFF,1:YmatrixFF,1:maxz);         % creation of a vector x with numbers starting from 1 to the value
                                                              % of XmatrixFF with the numbers of rows equal to the difference in 
                                                              % end and begin value of the y vector.
                                                              % And because its a 3D array there are two more of this 2D matrices.                                                                                                                         
[xi, yi, ~] = meshgrid(-maxx:maxx, -maxy:maxy, 1:maxz);         % This meshgrid creates an xi vector starting with the -maxx and going to +maxx
                                                              % And also creates an yi vector starting with -maxy and going to +maxy.
                                                              % The zi starts again with 1 and goes to maxz.

                                                                % [x,y,z]     = meshgrid(1:XmatrixFF,1:YmatrixFF,1:maxz);       
ri = round(sqrt(xi.^2 + yi.^2));           % The radius depends on the xi and yi from the meshgrid created above
ffilter = z < H(ri+1);                     % ffilter is the volume when the value of z is smaller than the height that corresponds to (ri+1)
                                           % The +1 is used to avoid the working with a radius of zero
  end

Thanks very much in advance

[Jan]

The code does not run. Does "r" mean "radius" and "h" mean "height"? What exactly is a "cylinder matrix"? What do you want to create?

[David van Nederpelt]

I'm sorry, I forgot to submit a part of the code. I edited it in so it should run now.

It's a matrix of ones representing a cylinder (with a radius of 30.5 and a height of 8.1280 times the factor) There is a small error in the round off but that doesn't matter.

So I want to create a cylinder (made up of ones) in a matrix which is the size of the radius and height times a factor.

[Jan]

What is "it" in "it is a matrix"? Do you mean the variable ffilter? Then the term "matrix" is confusing, because it is a 2D array by definition.

What exactly is the problem? It looks like ffilter is a 3D array with the points on a cylinder shape set to 1. "isn't completely filled with ones"? At lease the subarray ffilter(:,:,1) looks like a circle without any "filling".

[David van Nederpelt]

"It" is the ffilter yes.

I want it to represent a 3D object "a cylinder" by a 3D array of ones.

[David van Nederpelt]

Hi Jan,

The code is quite long so I added the file. The reason why the radius is a vector because I want to be able to create 3 different object (depending on the energy)

The answer you gave doesn't seem to work for now. Maybe I'm unclear in my writing. And the code helps

Thank you very much for helping me!

Answer 1

[Jan]

I'd use some simple code like this to create a 3D array with a cylinder filled by ones:

x    = -maxx:maxx;
y    = (-maxy:maxy).';
circ = (x .^ 2 + y .^ 2 <= R ^ 2);  % >= R2016b: Auto-expand
Cyl  = rempat(circ, 1, 1, maxz);

It is not clear to me, why your radius is a vector, why you interpolate r and why the two meshgrid commands are needed.

[David van Nederpelt]

Hi Jan,

The code is quite long so I added the file. The reason why the radius is a vector because I want to be able to create 3 different object (depending on the energy)

The answer you gave doesn't seem to work for now. Maybe I'm unclear in my writing. And the code helps

Thank you very much for helping me!