# How can I extract the slices of a 3D matrix in x-direction from a 3D matrix?

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Commenté : Javad le 12 Juil 2018
I have a 3D matrix, which is a model of the porous media of a rock. I want to extract three 3D matrices from it so that each contains the 2D slices in a specific direction, for example x. To be clear, the matrix x contains the 2D slices in x direction, y in y-direction and z in the z-direction. I appreciate any hint or help to solve my issue.
Regards
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James Tursa le 6 Juil 2018
It is unclear what you want. The original 3D matrix already has 2D slices in each direction that you can get at with indexing. E.g.,
xyz = original 3D matrix
k = whatever
xyz(k,:,:) --> k'th slice along x direction
xyz(:,k,:) --> k'th slice along y direction
xyz(:,:,k) --> k'th slice along z direction
Do you mean you want to permute the data so the slices are always in the first two dimensions? Or ...?
Dear James First, thanks for your answer. But I think my question was not clear. To be clear I explain more. I have 3D matrix, which is in fact a digital rock model. All the arrays of the matrix are 0 or 1. I want to draw the streamlines in it using the command 'streamline'. But this command need x, y, z. I want to extract these three matrices from my 3D matrix. Can you help me in this regard? Thanks

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### Réponse acceptée

Anton Semechko le 6 Juil 2018
Suppose you have G, which is a Y-by-X-by-Z 3D array, then
i-th xy slice:
G_yx=G(:,:,i); % Y-by-X array
i-th xz slice:
G_xz=permute(G(i,:,:),[2 3 1]); % X-by-Z array
i-th yz slice:
G_yz=permute(G(:,i,:),[1 3 2]); % Y-by-Z array
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Anton Semechko le 8 Juil 2018
Modifié(e) : Anton Semechko le 8 Juil 2018
I see. Let's say G is your Ny-by-Nx-by-Nz 3D image and [dx,dy,dz] are dimensions of a single voxel. To get get (x,y,z) coordinates of the voxels do:
[Ny,Nx,Nz]=size(G);
[x,y,z]=meshgrid((1:Nx)*dx,(1:Ny)*dy,(1:Nz)*dz);
The variables 'x', 'y', and 'z' have the same dimensions as G, and can be used as input to the 'isosurface' function along with G to extract a triangular mesh of the level-set surface G==1.
Dear Anton
Many thanks. It works

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